discussion with teacher

1. Request to show the final velocity of the carts only after collision. Currently, when I input the initial velocities, the final velocities are shown immediately, even before I click play


2. Request to display magnitude of F1 and F2.  Currently, when use "pause" function, vector arrow of F1 and F2 are shown but not its magnitude. Furthermore, the Force vector is often too long and goes out of the screen. Students cannot compare its magnitude.dd

[color=blue][b]reduce the length
show number now //force
 s_F1 = " { F_1 } = "+double2String(F1,1000.);
 s_F2 = " { F_2 } = "+double2String(F2,1000.);

3. Enlarge or zoom in the time of collision. i.e. enlarge the width of the spike in F-t graph.
Rationale: during collision, the force acts on the carts over a period of time. During this time interval, at any instant, the force acting on the two carts must be equal and opposite. Wants to emphasize this pt to the students.

[b][color=blue]cannot be done, because of the very short time during collision happens only of a small fraction of dt.
can zoom in but the period of time is a small fraction of dt thus it draws like a triangle. [/color][/b]

4. Related to pt 3, since the F-t graph now looks like a triangle, the force during collision is not constant. As such, the momentum-time graph must show a curve during collision.

[color=blue][b]Force acts for a very very short time, so it cannot be constant, it is a spike value.
so momentum is slope down or up depending on whether it is an decrease or increase of momentum.[/b][/color]

5. What is "game"? in the Java Sim. What is the function of this?

[color=blue][b]game is an assessment of learning, where student can try to key in values to check whether they understood the concepts in COM and COKE during collision.[/b][/color]