RipStik Deceleration

Acceleration is introduced by riding a RipStik up a slope while decelerating, turning around at the top of the slope, and then accelerating back downslope. Posts along the covered walkway provide timing points. Prior to going outside on Monday I sketched a graph on the board of what a time versus distance graph should look like if I rode with decreasing speed and then turn around and ride with increasing speed. The result is a roughly parabolic prediction. Note that negative velocity on a graph was also covered on Monday.

time (s)	split dist (cm)	distance (cm)	velocity (cm/s)	acceleration (cm/s²)
0	0	0
0.97	306	306	315.46		Running
2.13	305	611	262.93	-45.29	Avg Acc
3.69	307	918	196.79	-42.39	-44
6.72	316	1234	104.29	-30.53	-39
10	-316	918	-96.34	-61.17	-45
11.82	-307	611	-168.68	-39.75	-44
13.07	-305	306	-244.00	-60.25	-47
14.69	-306	0	-188.89	34.02	-35

Graphing the time versus the distance (third column) provides speed information from the slope. The students were given this as homework. 

On Wednesday I asked the students if they got the shape I predicted, which they did. Then I spent Wednesday showing them that a change in speed per unit time can be calculated, generating what I explained would be called acceleration. The students had the table above and the graph on a handout as reference.

I built from the slope of the above is the velocity to the slope of the velocity versus time is the acceleration.

I then drew attention to the acceleration always being negative until the final post and what that meant, negative with a slope of zero.

The handout also had the above chart. This then builds into measuring the acceleration of gravity.