Class Copy

# Video Measurement of Position vs Time

## Objectives

1. Gather data using an motion analysis application.
2. Learn how to make a position vs time graph.
3. Calculate average velocity using the data and graph.

## Materials

1. Ring stand with utility clamp
2. Ping-pong ball (or equivalent)
3. Meter stick (to measure position)
4. V-shaped plastic molding (used as a ramp to guide the ping-pong ball)
5. iPad with SmartMotion app.

## Directions

1. Work with your team to gather the data. Each person records the data and does calculations!
2. Use the ring stand utility clamp to hold an end of the plastic molding about 10cm off the table (The ramp should not be too steep).
3. The other end of the V-shaped plastic molding can rest on the table top.
4. Place the meter stick at the end of the plastic molding in the ball run-out zone.
5. Test Stand Top View
```                                                           Ring Stand
end   middle  begin                           _____
v      v       v          ramp              |    |
==============================O  |
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~                            |____|
meter stick
```
6. Release the ping-pong ball at the top of the ramp.
7. Use the ipad camera to capture a video of the ball as it rolls off the ramp and across the table.
8. Capture the first ≈30 cm of travel across the table.
9. Open the video in SmartMotion.
10. You may use the frame set feature to narrow down the part of the video you are most interested in.
11. Use the Next and Previous frame buttons to select the frame as the ball just leaves the ramp.
12. Record the beginning distance and time. If the ball is a blur select one portion of the blur as your point for measuring the first and last frame.
13. Use the Next and Previous frame buttons to select the middle frame you want.
14. Record the middle distance and time.
15. Use the Next and Previous frame buttons to select the last frame you want.
16. Record the ending distance and time.

Name:
Video Measurement of Pos. vs Time Data Table
Location on table Position (cm) Time (s)
begin

middle

end

1. Use UDRSS to calculate the beginning ball speed (beginning to middle).

2. Use UDRSS to calculate the ending ball speed (middle to end).

3. Use UDRSS to calculate the overall ball speed (beginning to end).

4. Is the beginning speed faster than the ending speed? Does this make sense?

5. Why would you expect the overall speed value to be in between the beginning speed and ending speed? Do your measurements fit this pattern?

6. Graph the time vs position. Time = x-axis.