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
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.

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