RFE 2001.08.07.001

In Two-Balls, varying the acceleration due to gravity affects both balls equally while air resistance and ball mass affects only ball 2 (the yellow one). Similarly, let varying the acceleration due to gravity affect only ball 2.

url: Acceleration/Due to Gravity/Simulate It/One Ball

2001-08-07 Hans Laue

BUG 2001.08.31.001 STATUS: OPEN

Two-Balls Applet: BUG: The units and the label for the x-axis are covered up by the control panel, as a result of adding the logo bar. This has been fixed for the One-Ball applet, but not for the Two-Balls applet. Do the same for the Two-Balls applet.
2001.08.31 Hans Laue

RFE 2001.06.10.001

Two-Balls Applet:
RFE: Add a button that when clicked will superimpose ball 2 on ball 1.
Done, DoubleClicking on the background anywhere switches between ball 1 and ball2 being in front.
2001.09.19 Arend Meetsma

url: Acceleration/Due to Gravity/Simulate It/Two Balls

RFE: It is often of interest to start both balls at exactly the same position, in order to compare differences in their subsequent orbits, e.g., when one ball has air resistance and the other one does not, or when the two balls start with different velocities. It is tedious to manipulate one ball into exactly the same position as the other. So it would be good to be able to accomplish this upon clicking a button. Or maybe instead of a button one could double-click on the ball. Maybe double-clicking is preferable because it would save a button. Also one could make both balls double-clickable. Whichever ball is double-clicked gets moved on top of the other one. Right now, it is always ball 1 that is on top, even if ball 2 has been moved last. It is sometimes desirable to have a choice in which ball is the one that is movable (and whose velocity vector can be dragged) when they are superimposed.
2001.06.10 Hans Laue

Double Clicking on the background will swap ball1 behind ball two. Double click again and it will sap back in front.
2001.09.19 Arend Meetsma

RFE 2001.07.04.001 STATUS: FIXED

A number of small changes in the Acceleration/Basic Facts/Explain It session. The text is already in place, and an applet on p.3. Other applets need to be added.

url: Acceleration/Basic Facts/Explain It

url: Torque/About An Axis/Apply It/Physical Pendulum

url: Interaction/Basic Facts/Get A Glimpse

The Acceleration/Basic Facts/Explain It session has eight pages. I will describe what needs to be done on each page.

• Page 1. There will only be the existing text.
• Page 2. On the left-hand side place the applet from Torque/About An Axis/Apply It/Physical Pendulum. Set the radius of the bob to 0.4 m and the length of the pendulum to 5 m. Select button 2 so that the velocity and acceleration vectors are displayed. Make all other buttons inactive, including the START/PAUSE button. The pendulum should be swinging as soon as the applet has loaded. It should be swinging between -120 deg and 120 deg. Text is on the right-hand side.
• Page 3. Place the 4-motions applet from Interactions/Basic Facts/Get A Glimpse on the left and text on the right, as has already been arranged. There are a couple of problems with the 4-motions applet. (a) When one selects choice (d), the response page has a 1-page pagebrowser at the bottom. Get rid of this. (b) Some of the applet is chopped off at the bottom because space is taken up for both the page navigator and the choice button navigator. Is there anything one can do about this? I could live with the way things are at present, although not ideal.
• Page 4. There will be only text on this page. No changes required.
• Pages 5-7. Divide the content area into an upper and a lower portion, about 2/3 for the upper and 1/3 for the lower portion. The new applet in which a velocity vector will be steered by means of an acceleration vector (Acceleration/Basic Facts/Simulate It/Accel. Vs. Veloc.) will be in the upper portion and the existing text in the lower portion. The full applet will be available on all three pages.
• Page 8. Existing text only.

(2001.07.04.001) Hans Laue

2001.08.30 DONE Jeremiah

RFE 2001.07.24.001

A number of alterations of the existing displacement applet are requested. These were worked out together with Gary Raab. I think they will significantly improve the applet.

The average velocity applet will have corresponding alterations. See under Velocity below.

url: Displacement/Basic Facts/Simulate It/

url: Velocity/Average/Simulate It

1. Add another button to the applet. The button is titled 'Initial Position'. Until this button is clicked and depressed, one can do nothing with the applet. When it is depressed, one can click anywhere on the screen to place the ball at that point. One can then drag the ball elsewhere as long as the mouse button stays depressed. As soon as the mouse button is released, the ball's position is set and the Initial-Position button is raised. The button could be clicked again and the ball's initial position could then be set somewhere else. When the button is clicked and one clicks on the ball itself while it is still at the origin, the ball's position does not get changed, unless one drags the ball.
2. After clicking the Initial-Position button, if one drags the ball with the shift key depressed, the ball moves along a horizontal, vertical or 45⁰ direction, whichever is closest to the direction in which one is dragging.
3. Add a button labeled 'Position Vectors'. When clicked, this button will draw position vectors to the initial and final ball positions. These vectors will be labeled r_i and r_f, respectively. The r will have an arrow above it.
4. Add a 'grid' toggle button that will extend the x,y axes to a grid, to make it easier to set the position of the ball to a grid point.
5. To make it easier to set the ball to a grid point, replace the ball by a 'hollow' one (transparent may be a better word) with a pair of horizontal and vertical diameters inside the ball to define the center point of the ball, which then can be aimed towards a grid point.
6. Enhance the tip of the green displacement arrow so that one can see clearly in which direction the arrow is pointing.
7. Change the display of the numerical values as follows. In the top left corner, create a column headed 'distance traveled' and in the top right corner a column titled 'displacement'. To the left of the title 'distance traveled' draw a small red square color-coded with the red curve traced out by the ball. To the left of the title 'displacement' draw a small green square color-coded with the green displacement vector.

   The only entry under 'distance traveled' is 's = ... m'. This is currently the last entry on the right.

   The only entry under 'displacement' is d = (d,q) = (... m, ... deg). The d should have an arrow above it, as should all boldface symbols listed in the following paragraph.

   Add a toggle button titled 'More Data'. When that button is depressed, the following additional entries are placed in the displacement column on the right underneath the one entry described in the preceding paragraph:

   r_i = (x,y)_i = (...,...) m
   = (r,q)_i = (... m, ... deg)

   r_f = (x,y)_f = (...,...) m
   = (r,q)_f = (... m, ... deg)

   d = Dr = (Dx,Dy) = (..., ...) m
   = (d,q) = (... m, ... deg)

(2001.07.24) Hans Laue

BUG 2001.06.01.001

In two questions of the listed item, the Submit and Give Up buttons on the Question Navigator do not show the button labels properly. Also, the numerical entry down arrow in the first of the two questions does not get fully displayed.

url: Electric Circuits/Potential/Test Yourself/Pot'l Divider 1/
url: Electric Circuits/Potential/Test Yourself/Pot'l Divider 2/

In the Potential Divider 1 Question, when one submits an incorrect answer, the Back-To-The-Question button does not show the last 'n', but shows an empty rectangle before 'Question'.

In the Potential Divider 2 Question, the Give-Up button does not show the final 'p' but shows an empty rectangle before 'Up'.

In both questions, the tool tip in the Location Tracker that goes with Test Yourself extends beyond the left edge of the screen. It is probably silly to have tool tip info here anyway, but in general this problem should not exist. What determines the location of the tool tip rectangle?

In the Potential Divider 1 Question, only the top portion of the down arrow of the numerical entry field is displayed. It should be visible in its entirety.

(2001.06.01) Hans Laue

RFE 2001.05.03.001

Add energy meter and h-scale to double-incline, Atwood, and block-and-pulley applets, as in Fletcher Trolley. Also, implement the other features, i.e., fbd's, with stippled tensions when blocks are being dragged, question marks where appropriate, printouts like "Animation paused" as appropriate, etc.

url: content/energy/energy_cons/simulate/dbl_incline/
url: content/energy/energy_cons/simulate/atwood/
url: content/energy/energy_cons/simulate/block and pulley/

The same things as done in the fletcher applet apply also to the double incline applet, the Atwood machine applet, and the block suspended from pulley applet (i.e., completing Shane's work)
(2001.05.03) Hans Laue

RFE 2001.05.30.002

Replace Edmonton library animation with our own in Potential Energy/Explain It/Uniform Force on p.4.

url: Energy/Potential Energy/Explain It/Uniform Force/

On p.4 - 12 of Energy/Potential Energy/Explain It/Uniform Force the applet requires the Edmonton library, while the similar applets on earlier pages don't require this library. I think the only thing the Edmonton library is used for is the animation. It is our applet. It would be good if we could replace the animation with our own routine, unless a lot of work is required. Use the same routine as in Acceleration/Due to Gravity/Simulate It/One Ball. We are dealing with projectile motion in the present applet, as we are in One Ball. (The energy bar needs to be animated too, of course.)
(2001.05.30) Hans Laue

BUG/RFE 2001.06.10.001

Some small adjustments and rfe's need to be made. See below.

url: Energy/Energy Conservation/Simulate It/Fletcher

When block 2 is resting on the platform (either after lowering block 2 or raising the platform), the vectors F and T1 in the fbd for block 1 should be absent (because there will be no force needed to hold block 1 at rest and because the string will be slack), and the tension T2 in the fbd for block 2 should be replaced by an upward normal force vector labeled 'N' and equal in magnitude to W2. The normal force vector should be in blue (0,0,255). Just use the color constant for normal force. There should be a comment on the screen saying "String is slack". This comment will be in the same place where the other comments are placed, e.g., "Blocks held at rest".

However, as soon as block 1 is being moved left, the applet should behave as at present, except that the tensions should be shown stippled (like F) rather than greyed out. The symbols F and T1 and T2 should have question marks behind them as at present, but not be greyed out (to make them easier to see). The color of the force vector F should be red (constant color for friction), and so should be the label 'F'. The tip of F vector should be the same as the tips of the other vectors.

There should be a black dot at the center of each fbd, to symbolize the object the forces are acting on.

Raise fbd 1 slightly so that the F vector when extended is above the value for KE1. When the mass of block 1 increases, the label T1 of the tension jumps from below the vector to above the vector. Keep it below the vector at all times.

Write all variables in italics, including KE and h.

The motion is still a bit jerky, particularly evident in the speedometer. Is there anything one can do to make it smoother? Low priority for this request and can be ignored.
2001.06.10 Hans Laue, updated on 2001.08.15 Hans Laue

RFE 2001.08.15.001 STATUS: OPEN

In the energy race, do not convert the potential energy blocks to kinetic energy blocks randomly, but linearly, starting at top left for TK (translational kinetic energy) and at bottom right for RK (rotational kinetic energy).

url: Energy/Energy Conservation/Simulate It/Energy Race

Details:
It will be easier to compare the amounts of TK and RK if they are grouped in blocks. The left/middle/right ordering of the colored blocks agrees with the ordering of the TK/PE/RK labels underneath.

Also, stop the motion when all the PE is used up for one of the two objects.

2001.08.15 Hans Laue

BUG 2001.08.15.001 STATUS: OPEN

Several small bugs are listed here. ('Small' in the sense of not causing major functionality problems.)

url: Energy/Energy Conservation/Simulate It/Energy Race

Details:

1. When the applet first comes on (default state), both inclines are frictionless. However, the friction buttons both read "Turn Friction Off". They should read "Turn Friction On". The buttons do function properly, i.e., when clicked they turn the friction on and then read "Turn Friction Off".
2. When an object is selected, the button for that object should indicate that the object is on the incline. At present, when one object is selected, the button does acquire a green rectangular frame. However, when the second object is selected, the first button becomes unselected. Both buttons should stay selected.
3. At present, one has to click the START button twice to get the motion going. The motion should start on the first click.
4. Replace the RESET icon by the REPLAY icon, because this is the functionality of the button. We don't need a RESET button here.
5. Add the logo bar and remove the question mark button. Space for the bar can come out of the white space at the bottom of the area showing the colored blocks and out of the grey divider between the top and bottom halves of the applet window.

2001.08.15 Hans Laue

RFE/BUG 2001.09.12.001

There are several changes and enhancements required as detailed below. In addition, Gary wants a version with only a single particle (no 2 or 12 particle options). Let's call this 'Particle in Electric Field (Reduced)'. Otherwise, this applet is like the others.

url: Force/Electromagnetic/Simulate/Electric

Details:

• The data table at top right should have the colon immediately after the variable symbol, not just before the value. At present, there are two colons in the line for the time t. Delete the second one. Add a space before m/s^2 after the acceleration value.
• Change the color of the velocity vector from green to magenta. Change the color of the velocity components from black to the new official color.
• For Gary's one-particle applet, provide separate sliders for q and m, not a single q/m slider. The q-slider should let you set values of the charge in integer steps from -5 C to 5 C. The m-slider should let you enter mass values in integer steps from 1 to 5 kg. The value of q/m should be printed out in C/kg in the control box area, somewhere near the two sliders in a logical place.
• The charge sign toggle button should be deleted, because we can set the sign now with the q-slider.
• Try to re-arrange the various items on the control panel in a more logical and pleasing manner. E.g., the two buttons controlling the velocity and its components should be added to the collection of the other buttons on the left.
• Delete the question-mark Help button, and add a MAP logo bar with drop-down menu and Info file.

The following changes affect only the 2-particle and 12-particle modes and can be implemented later. Maybe it would be easiest to make a totally separate 1-particle applet for Gary, starting with a copy of the existing applet and stripping everything that is not needed.

• In the 2-particle mode, there should be two velocity vectors visible initially. Currently there is only one vector visible and adjustable. When one runs the simulation and clicks REPLAY, a second mustard vector becomes visible. It should be visible and adjustable right from the start.

  In this mode, de-activate the velocity-components button, and let the display-velocity button act on both velocity vectors, so that either both of them are displayed or hidden. (At present, the button does not do anything in this mode.) If both are displayed, keep them displayed during the motion. (At present, only the velocity vector of particle 1 moves along with the particle.)

• In the 12-particle mode, de-activate both the display-velocity and velocity-components buttons.
• In the 12-particle mode, REPLAY does not work properly. It does not move the particle back to the origin and, if one changes the field direction, the new motion is not oriented relative to the new direction.

2001.09.12 Hans Laue

BUG 2001.06.06.002

In the E-applet, the animation is incorrect when is something other then the default value.

The motion does not respond to settings of the |q|/m slider.

url: Force/Electromagnetic/Simulate/Electric

When the -vector is set to a vector that is rotated counter-clockwise a bit and the velocity vector is changed to be perpendicular to the new , and the charge is negative, the trajectory is not a parabola with the field direction at its axis. It crosses over the field direction. Perhaps the value of is not properly implemented in the animation.
2001.06.06 and 2001.09.12 Hans Laue

RFE 2001.06.06.002 STATUS: OPEN

In the B-applet, re-arrange the sliders so that they suggest the ratio m*v/(q*B).

Delete the unit 'C' with the q-slider. Relable the Mass slider with 'm'. Change the 'r' prinout.

url: Force/Electromagnetic/Simulate/Magnetic

Move the v-slider to the right of the m-slider. Move the B-slider to the right of the q-slider. This way the arrangement of the 4 sliders is in the order of the ratio m*v/(q*B) that is equal to the radius r that is printed out above.

Make sure that this arrangement works also for the small-scale version of the applet in the Explain It item. It may be useful to move the B and the 1X buttons underneath the other buttons.

Delete the unit 'C' in the q-slider. None of the other sliders have units.

Change the printout of 'r' to reflect the way 'r' is calculated. Thus, write

r = (m*v)/(q*B) = ...

Don't write any of the multiplication signs or parentheses. Write 9 in front of a fraction that is written with a real horizontal fraction bar and has 'mv' on top and 'qB' on the bottom.

Instead of the label 'Mass' for the m-slider use 'm', to be consistent with what is done for the other sliders and to introduce the symbols.
(2001.06.06) Hans Laue

BUG 2001.09.12 STATUS: OPEN

Changing values with the sliders does not always lead to correct values of r as printed out at top right.

Delete the question mark button for Help and add the MAP logo bar and link it to an info page.

url: Force/Electromagnetic/Simulate/Magnetic

Details:
The default values of m, v, q, B are 1, 1, 3, 2. Change m to 2, v to 3, and observe the corresponding changes for r. At this point, you should have r = 9. Now just click on the q-slider without moving it. The applet changes the value of r to 4.5. Of course, the value should stay at 9. I have not checked if the animation displays a radius equal to 4.5 or 9.

The values of r that should be displayed are given by the equation in the preceding RFE, namely, r = (m*v)/(q*B).
2001.09.12 Hans Laue

BUG 2001.06.06.004

In the B-applet, it can happen that clicking on the slider when q = 3 will produce a change in r-value, both the printed r-value and the simulated r-value.

url: Force/Electromagnetic/Simulate/Magnetic

When m=2, v=3, q=3, B=2, an r-value of 9 is displayed, which is correct. If one now clicks on the q slider, the slider tab, the r-value changes to 4.5 while the q value remains at 9. If one now changes the q-value to 1, the r-value increases by a factor of 3 to 13.5. Thus, things are consistent from this point on, if one takes 4.5 as correct. The system behaves as if the scale factor of 9 in front of the formula m*v/(q*B) has become reset. This effect does not occur for other settings of m, v, q, B.
(2001.06.06) Hans Laue

BUGS/RFES 2001.06.14.001

This is a copy of an email message dated 01-05-25 requesting a number of changes to the ExB applet. I am reproducing the email message below.

url: Force/Electromagnetic/Simulate/ExB Drift

Here are my thoughts on the ExB applet. I am assuming that things are programmed via a Galilean transformation to the drift frame. The steps should be as follows.

I will use the <...> notation to denote a vector, e.g., <v> to denote a velocity and v the magnitude of the velocity.

I will use vp to denote the numerical value of the variable v expressed in pixels and vu to denote the numerical value of v expressed in some given unit of v. ('u' stands for unit.) Similarly, Ep and Eu for the numerical values of E in pixels and in E-units, etc.

1. One gets <vin> in pixels from the green arrow. This yields vinp and the angle of <vin#62.
2. One calculates the drift velocity <u> = <E>X<B> in whatever units E and B may be given. First, one obtains Ep from the red arrow and then transforms Ep by means of a scale factor to a new Eu. Let the maximum value of this new Eu be 0.001, say. (I think the program has 0.5 at present.) And let the minimum value of Bu be 1. Then this would give a maximum value of uu = 0.001. (The reason I am choosing these funny values is that u must be much less than the speed of light for the equations to be physically accurate, and I am taking the speed of light equal to 1, in u-units. It would not matter if in the simulation we chose uu to be much bigger than 0.001, but it helps me in visualising things if I use uumax = 0.001.)
3. Before going to the next step one must now invent a scale factor that translates the pixel units of <vin> to u-units. Suppose we want uumax = 0.001 to be represented by 50 pixels. Then vu = 1 corresponds to 50,000 vp and 1 vp corresponds to 2x10^-5 vu. Thus, if <vin> is 100 pixels long, then vinp = 100 and vinu = 0.002.
4. In the following, let us work with a velocity scale factor such that a numerical value of vp = 1 corresponds to vu = 0.00002 and with an E-field scale factor such that an Ep = 120 (or some value like this) corresponds to Eu = 0.001.
5. Now calculate <v'in> = <v> - <u>, where <v'in> is the initial velocity in the drift frame. Here v and u must be in the same units, either pixel units or u-units. v'in will then be in these units as well.
6. Now calculate the orbit in the drift frame. This is done by calculating <v'(t)> rotating the vector by 90 deg, and multiplying it by a suitable scale factor C to get a display that fits on the screen. The resulting vector is denoted . It is the position vector in the drift frame. The scale factor C used here is unrelated to the other scale factors and is quite arbitrary because it simply determines the scale of the representation in position space. One cannot make a 'mistake' by choosing C incorrectly, other than that the circle in which the particle moves might be too large or too small for inspection.

To calculate <v'(t)>, one can use closed expressions of the form v'x = v'in*cos w*t and v'y = v'in*sin w*t, where v'in = const (calculated in Step 3) and w = (q/m)*B. w too needs to have a scale factor D which will determine the speed of the animation, i.e., the rate at which the particle is performing one revolution.

Did Jonathan use closed expressions like these or did he use a numerical integration? If one does a numerical integration, one must use for the acceleration the vector product (q/m) <v>X<B>, i.e., ax = (q/m)*B*v*y and ay = -(q/m)*B*v*x. Again, there needs to be a scale factor introduced into these equations that will determine the speed of the animation. (Varying the scale factor is equivalent to varying the size of the integration time step dt because the expressions for ax and ay are multiplied by dt.)

Step 4 yields <r'(t)>, the position vector of the particle in the drift frame, e.g.,

x'(t) = C*v'in*sin D*w*t.

It is assumed here that w is calculated in u-units for q/m and B and v'in is calculated in u-units as well. C is chosen so that x' and y' are in pixel units.

7. Now calculate <r(t)> = <r'(t)> + <u>*t, the position vector in the lab frame. We want <r(t)> in pixel units and must make sure that the two terms <r'(t)> and <u>*t are both in pixel units. We already have <r'(t)> in pixel units.

   The speed of a point on the <r'>-circle in pixels per time unit is C*v'inu*D*wu. We must introduce a scale factor F that translates uu to up = F*uu such that

   C*v'inu*D*wu/up = v'inu/uu.

   Thus,

   C*v'inu*D*wu/(F*uu) = (v'inu/uu) * (C*D*wu/F) = v'inu/uu

   whence

   C*D*wu/F = 1 or F = C*D*wu.

   Thus, we get <r(t)>p = <r'(t)>p + F*<u>u*t.

(2001.06.14) Hans Laue

BUG 2001.08.15.001 STATUS: CLOSED

The vector colors in the Block-on-Spring-Scale applet need to be changed, and the labels on the two sliders require more room.

url: Force/Normal Force/Explain It/Quantitative

Details:
Change the normal force, weight, and acceleration vectors to the color constants (blue, dark green, orange).

Add a space between "2.00" and "kg" in the mass label for the block.

Label the acceleration slider as "Accel." so that there is enough room to display the value of the acceleration and its unit. Similarly, label the velocity slider as "Vel." so that there is enough room to show the entire unit.

2001.08.15.001 Hans Laue

Arend was here

RFE 2001.08.15.001 STATUS: CLOSED

Change the spring compression animation and change the default position of the table.

url: Force/Normal Force/Explain It/Quantitative

Details:
In the default setting, the table top is just below the 19.60 N text for the weight. When the acceleration is then made unequal to zero, the springs get compressed or expanded around their mid level. Thus, upon contraction of the springs, the top of the springs and the block come down and the bottom of the springs and the table come up an equal amount.

2001.08.15 Hans Laue

I did this some time ago - Arend

RFE 2001.05.28.001

Torque/Basic Facts/Explain It/

url: Torque/Basic Facts/Explain It/

On p.1 - 7, draw the trace of the CM as a continuous curve, not by means of dots that do not correspond to equal time intervals.
(2001.05.28) Hans Laue

BUG 2001.05.28.001

On p.1-7 of lesson, make STEP button active immediately.

url: Torque/Basic Facts/Explain It/

On p.1 - 7, the STEP button only becomes active after clicking PLAY and PAUSE. It should be active right away.
(2001.05.28) Hans Laue

BUG 2001.05.28.002

CM of pendulum on p.8 or 9 cannot be dragged at first.

url: Torque/Basic Facts/Explain It/

On p.8 and 9, the CM of the pendulum cannot be dragged when the applet is first loaded. One must first play the animation and then reset it before one can move the CM by dragging. One should be able to drag the CM right away.
(2001.05.28) Hans Laue

BUG 2001.05.28.003

RESET does not work properly in physical pendulum. There also should be a RESTART button.

url: Torque/Basic Facts/Explain It/

On p.8 and 9, when one clicks RESET after pausing the pendulum, the pendulum is not restored to its default position, but stays where it is. Only when one clicks on the pendulum, after clicking RESET, is the pendulum restored to its default position. However, even clicking will not return the pendulum's default settings. E.g., the pendulum's size will not be restored to the default value. Also, the buttons will not become deselected. There should also be a RESTART button that is distinguished from the RESET button in the usual way.
(2001.05.28) Hans Laue

BUG 2001.05.28.004

In physical pendulum on p.8, PLAY and RESET don't act properly.

url: Torque/Basic Facts/Explain It/

On p.8 and 9, PLAY acts like a RESTART button after RESET. RESET does not restore the applet, but PLAY following RESET causes the applet to restart the motion from the previous starting point. This should not be so. PLAY should start the motion at the point at which the pendulum is at rest.
(2001.05.28) Hans Laue

BUG 2001.05.28.005

In pendulum applet on p.8 or 9, display constraint force before clicking PLAY.

url: Torque/Basic Facts/Explain It/

On p.8 and 9, when button 1 is selected, only the gravitational force is shown before the start of the motion. When the motion is started, also the constraint force is shown. The constraint force should be shown whenever the gravitational force is shown. Basically, the display should correspond to reality in a state of frozen animation. At the instant of frozen animation when the pendulum is at rest, the constraint force is not zero. It may be quite small for certain pendulum settings. Set the radius of the disk to 4 m, and the constraint force will be significant, even when the velocity of the CM is momentarily zero.
(2001.05.28) Hans Laue

BUG 2001.05.29.006

On p.2 (and other pages), there should not be any motion upon PLAY when the net torque is printed as 0.

url: Torque/Basic Facts/Explain It/

On p.2 and other pages, when one adjusts the force vector so that the net torque is 0 and then clicks PLAY, there is a slight rotation of the square object, or sometimes not so slight. The applet should not show any motion whatsoever when the net torque is printed out as zero. There should be a small, but finite-sized 'bin' of settings at which the net torque is printed out as zero. In all of these settings, there should be no motion upon PLAY.
(2001.05.29) Hans Laue

BUG 2001.05.29.007

RESET DEMONSTRATION tool tip on Reset button after running animation stays on too long.

url: Torque/Basic Facts/Explain It/

Go to p.3, say, and point the mouse over the RESET button. The tooltip displayed is RESET DEMONSTRATION. It remains visible way too long after moving the mouse pointer off the button. This may or may not be related: When one returns to the Presenter after typing this bug report in Secure Shell, it takes the Presenter forever to regenerate the various applets on p.3 with buttons and pagebrowser buttons.
(2001.05.29) Hans Laue

BUG 2001.05.31.008

Very slow restoration of applet after using another application, e.g., Secure Shell to edit text.

url: Torque/About An Axis/Explain It/

Suppose you are on p.4 of this item and then use Secure Shell to edit some of the text and then return to page 4, it takes a very long time for page 4 to get restored: the pagebrowser is missing at first, and so are the buttons under the applet. These items get restored one by one very slowly and may never get completely restored. It seems to help to move the mouse pointer over the places where the buttons are supposed. Some buttons come on when one is doing this.
(2001.05.31) Hans Laue

RFE 2001.05.03.001 . . . . CLOSED (2001.05.24) ... REOPENED (2001.06.11) CLOSED (2001.08.10)

Enhance cursors and endpoints of vectors.

url: content/vectors/addition/simulate/twomethods/
url: content/vectors/addition/simulate/threevec/
url: content/vectors/subtract/simulate/

Modify existing Add Vectors applets (2 or 3 vectors) to enhance user interface: special vector drawing cursor, require button selection before enabling certain draw modes, have endpoints of vectors better defined, etc.

(2001.05.03) Hans Laue

Done.
(2001.05.24) Arend Meetsma

Remove the black outline from the vectors to make the dots at the two ends of the vectors stand out more. Do this also in the vector subtraction applet.
(2001.06.11) Hans Laue

Done. For subtraction and addition and scalar and all applets deriving from VectorPanel.java
(2001.08.10) Arend Meetsma

RFE 2001.05.03.002 . . . . CLOSED (2001.06.08)

New Applet

url: content/vectors/basic/explain/2
url: content/vectors/basic/simulate/2

Simulate vectors in three modes that illustrate three ways of specifying vectors
(2001.05.03) Hans Laue

These two applets have been added, they are called '2' in the directory structure.
The explain it item has four pages and forces the student to look at each way of specifying a vector.
The Simulate it item lets the student switch between the modes with the radio buttons on the control bar.

(2001.06.08) Arend Meetmsa

RFE 2001.05.03.003 . . . . CLOSED (2001.08.10)

New Applet

url: None yet

Applet that allows adding an unspecified number of vectors and that adds vectors automatically on screen after vector coordinates (either polar or cartesian) have been entered
(2001.05.03) Hans Laue

This applet could use the same functionality as the Specifications Applet as far as vector specification is concerned. Before a vector is added, the student selects one of the 4 modes for specifying the vector, then adds the vector. The resultant vector too can be displayed in any of the four modes.
Start the applet with a small cross in the middle of the screen to mark the point at which the tail end of the first vector will be placed. This cross can be dragged at any time, to allow better placement in case the sum of the vectors should extend beyond the edges of the window.
Then, when the first vector has been specified, the system will display it when an ADD button is clicked. Then when the next vector is specified, the system will join it tip-to-tail to the first vector when and ADD button is clicked.
There is a RESULTANT button that will display the resultant on the screen when clicked and will display its coordinates, in any of the four forms chosen.
The vectors don't need to be labeled.
One can add as many vectors as one likes, but the magnitudes of the vectors that one can add are restricted so that the sum of three vectors can always be made to fit on the screen. Say, let the magnitude of a vector be restricted to 100 pixels. The system could display magnitudes directly in pixels (or perhaps pixels/10 and show one decimal point).
(2001.06.08) Hans Laue

This applet is finished. <- that's a period.
Any bugs found are hereby declared 'features'
(2001.08.10) Arend Meetsma

BUG 2001.05.28.001 . . . . CLOSED (2001.05.30)

On p.2, do not change cursor when moving onto vector.

url: Vectors/Basic Facts/Explain It

On p.2, when the cursor is moved onto the vector, it changes to a crossed double arrow cursor. However, no special action is available and none is required. The cursor should not change in this case. (It should on a later page, where is required to be able to drag the vector.)
(2001.05.28) Hans Laue

Fixed, cursor works as it should now.
(2001.05.30) Arend Meetsma

BUG 2001.06.01.001

On pages 3 to 5, show vectors with some orientation as is chosen by student on p.2.

url: Vectors/Scalar Multiplication/Explain It

On p.2, a student can arrange the magnitude and direction of the vector. On p. 3 this vector is maintained and a second vector equal to the first one is added. This is as it should be and should not be changed.

On p.4, the vectors a and b are shown with different magnitudes than the default value on p.2. The vectors on p. 4 should be as follows: for it should be the vector chosen by the student on p. 2, and for _b_ it should be the negative of this vector. Also, the minus sign in front of _b_ should be more visible.

On p.5, there should be with the direction and magnitude chosen on p.2 and the corresponding b = - a.

If students randomly jump around between pages 2 and 5, after having chosen a vector on p.2 initially, the system should always use as the default the vector chosen by the student on p.2. Only on p.2 can the direction of this vector be changed by the student.

If students directly jump to one of the pages 3-5 initially, from p.1, without ever going to p.2, the default vector should be the vector presently used by the system.

(2001.06.01) Hans Laue

RFE 2001.06.12.001 CLOSED (2001.09.19)

This is a new applet. It is a modification of the existing 2-vector addition applet, but will be used as a separate applet in addition to the existing one. The new applet has all the action on one page while the existing applet spreads the action out over several pages. Gary Raab has requested this applet.

url: Vectors/Addition/Simulate It/Two Methods

The present applet has three buttons. The new applet will five buttons. I am describing the five buttons one by one in the order from left to right. The present DELETE button will exist no longer and will be replaced by a RESET button that deletes everything and resets the applet to the initial state.

• Button 1 (old): Draw-Vector button that lets you draw a vector after the button has been clicked. At the beginning, this is the only button that is active. The button must be clicked again before the second vector can be drawn. After the second vector has been drawn, the button becomes inactive. Both vectors can be changed and moved around freely. The two vectors are labeled 'a' and 'b'.
• Button 2 (new): Draw-Resultant button. When clicked, the system will draw the correct resultant if more than one vector is on the screen. The resultant will be drawn in green off to one side as on p.4 of the existing applet and labeled 'a + b'. If there is only one vector on the screen, the Resultant button is inactive. The icon for the Resultant button is a double vector slanted like the single vector on button 1.
• Button 3 (old): Dotted-Line button that works as at present and lets you draw a dotted line at any time.
• Button 4 (new): Reset. Restores applet to its initial state with an empty window and only button 1 active.
• Button 5 (new): My-Answer button. When this button is pressed, the student can draw his sum of the two vectors on the screen. The vector will be labeled 'my sum' as at present. After the vector has been drawn it can be modified an moved around, so there is no need for an Eraser button. It would be nice to have an icon for this button, but maybe 'My Answer' as a label is clearest.

(2001.06.12) Hans Laue

Done
2001.09.19 Arend

BUG 2001.06.12.001 IMPORTANT and easy to fix! CLOSED (2001.08.10)

In the Vector Addition/Explain It/Tip-To-Tail applet, there is a rapid flicker on p.1 and subsequent pages when one moves the mouse pointer over the Next Page arrow without clicking on the arrrow. The flicker does not stop right away when one moves the mouse pointer off the arrow. The tooltip never appears.

I would suggest to remove the tool tip for the forward and back arrows and for the page number buttons. I think this is what is causing the trouble, and the function of these items is obvious anyway.

DO THIS EVERYWHERE, NOT ONLY IN THIS ONE ITEM. THE TOOLTIPS ARE NOT NEEDED FOR THE PAGE NAVIGATOR AND HAVE BEEN REMOVED IN THE AUTOMATED PAGEBROWSER.

url: Vectors/Addition/Explain It/Tip To Tail

The same problem also occurs with some other applets in the Vector area. I have not made a systematic chekc of it. When done, please report below what the cause of the problem was. Then we will know when we find the next applet with the same problem.
(2001.06.12) Hans Laue

It seems that the tooltips would not load up properly if the pagebrowser was not tall enough. This was only reproducable on windows boxes. Tooltips have been shut off on the pagebrowser. (2001.08.10) Arend Meetsma

RFE 2001.06.12.002 . . . . CLOSED (2001.08.10)

In the Vector Addition/Explain It/ applets, and also in the Simulate It and corresponding Vector Subtraction Applets, remove the black outline of the arrows so that the dots at the ends of the vectors become more distinguishable.

url: Vectors/Addition/Explain It/Tip To Tail

There are several more URL's in the areas of Vector Addition and Vector Subtraction that all should be treated the same way.

(2001.06.12) Hans Laue

Done. For subtraction and addition and scalar and all applets deriving from VectorPanel.java
(2001.08.10) Arend Meetsma

RFE/BUG 2001.06.12.003 . . . CLOSED 2001.08.10

In the Vectors/Basic Facts/Explain It/Vector Specific's applet, make a number of enhancements and changes as detailed below. Apply these also to the Simulate It version of the applet.

url: Vectors/Basic Facts/Simulate It/Vector Specific's

url: Vectors/Basic Facts/Explain It/Vector Specific's

1. In the Cartesian mode, indicate the components vx and vy in terms of colored bars on the axes, as is done in Vectors/Scalar Components/Explain It/ p.2, and label these components vx and vy. Otherwise one does not know where these pieces are.
2. Can you move the v-label of the vector a bit closer to the middle of the vector?
3. In the grey controls area, can you put an arrow over the v-symbol?
4. The word "Cartesian" needs to be moved left close to the radiio button.
5. You already told me that in the Navigational mode there needs to be a compass with the four basic directions in one corner.
6. The word 'degrees' should be abbreviated to 'deg' everywhere.

(2001.06.12) Hans Laue

I'm calling this one closed. It's done except for a few ComplexString issues in the cartesian label.
(2001.08.10) Arend Meetsma

BUG 2001.07.12.001 . . . . CLOSED (2001.08.10)

In Vector Specification applet, in the positive angle mode, one can enter negative angles. This should not be possible.

url: Vectors/Basic Facts/Simulate It/Vector Specifica'n/

If one enters a negative angle, the angle is displayed correctly as a negative angle. This should not be allowed. At present, if one enters something like a80, the computer pings and does not respond otherwise. The same should happen if one enters -80.
(2001.07.12) Hans Laue

DONE. The applet beeps whenover these values are entered.
(2001.08.10) Arend Meetsma

BUG 2001.07.24.001 . . . . CLOSED (2001.07.31)

This is not really a bug, but an alteration. It concerns the list of 8 navigation possibilities in the Vector Specification and Multiple-Vector Addition applets. It was requested by Gary R. and is quite reasonable and systematic.

url: Vectors/Basic Facts/Simulate It/Vector Specifica'n

url: Vectors/Addition/Simulate It/Numerical/

At present the list starts with WofN and then goes on to EofN, relating angles to north. We would like to bump the first item, WofN, to the end of the list and keep the sequence of the other items unchanged. Thus, the new list will be, in sequence, EofN, NofE, SofE, EofS, WofS, SofW, NoW, WofN. This way the first two pairs will give vectors in the first quadrant if the angle is less than 90 degrees, which is what students will want to do most, and each subsequent pair involves the same pair of geographic directions, i.e., E/N, S/E, W/S, N/W.
(2001.07.24) Hans Laue

Done
(2001.07.31) Arend Meetsma

RFE 2001.07.25.001

This applet needs several enhancements that are parallel to those suggested in RFE 2001.07.24.001 under Displacement. Compare the items listed there while reading through the details below.

url: Velocity/Average/Explain It

url: Velocity/Average/Simulate It

url: Displacement/Basic Facts/Simulate It/

Items 1 - 6 from the Displacement applet should be implemented here as well.

Add a new item 1a:

1a. After the ball has been set (or the ball may still be sitting at the origin without anything having been done to it), it should be possible to drag the ball to another location, as at present. In order to do so, one must click on the ball and drag it. Clicking outside the ball should not produce a movement. When clicking on the ball one should be able to click anywhere inside the ball without affecting the starting position. The entire ball should be the handle by which one can drag the ball. This is implemented already, I believe.

The clock should start running the instant one clicks on the ball. This is NOT implemented at present. At present, the clock starts running when one is actually moving the ball. As implemented at present, the clock should stop running when one releases the mouse button, not when one stops dragging the ball.

One should be able to click on the ball again and drag it to another place, to be able to carry out a number of displacements in succession with the clock being paused in between. The displacement vector will be the overall displacement vector. These things are already implemented.

Item 7, the data display, needs to be modified as follows.

The headings in the top left and right corners should be changed to 'average speed' and 'average velocity', respectively, color-coded as the corresponding items in the Displacement applet. Under 'average speed' there are three entries, in the following order:

s: ... m
t: ... s
v_av: ... m/s

Under 'average velocity' there are three entries, in the following order:

d = (d,q): (... m, ... deg)
t: ... s
v_av = (d/t,q): (... m/s, ,,, deg)

The toggle button 'More Data' adds to the three items under 'average velocity' the same set of extra items as in the Displacement applet, plus the following additional one at the end of that list:

v_av = Dr/t = (Dx/t,Dy/t): (..., ...) m/s
v_av = (d/t,q): (... m/s, ... deg)

(2001.07.25) Hans Laue