Introduction
In this practical the motion of a ball rolling off the end of a ramp will be analyzed using video. If you are using an Apple computer the program quicktime can be used to record the webcam. If you are using a PC then download the program “Debut” from http://www.nchsoftware.com/capture/index.html.
Note: Record in mov format so that loggerpro can open the video.
Research Question
What is the relationship between the velocity of a ball after rolling down a slope and the height of the slope?
Independent variable: Height of slope (h)
Dependent variable:Final velocity of ball (v)
Controlled variables:
Angle of slope
Size and mass of ball
Nature of surface of slope
Nature of surface after slope
Theory
When a ball rolls down a slope it accelerates with a constant acceleration of gsinϑ (ignoring friction and air resistance).
If acceleration is constant then v2 = u2 + 2as
But if the initial velocity = 0 then v2 = 2as
But a = gsinϑ where sinϑ = h/s
So v 2= 2gsh/s = 2gh
Method
The velocity of the ball is going to be measured by analyzing a video. This can be done using your webcam or a camera.
- Position the camera so that it records the motion of the ball after the slope (this region must be flat so that the velocity of the ball changes as little as possible).
- Make 6 marks on the slope at different heights with some tape. These will be the starting points. Measure the height h of each point.
- Make two marks a distance of 50cm apart on the flat surface (table) with tape. These will be used to calibrate the video so must be in the picture.
- Place the ball on the marker, start the camera and release the ball.
- Without stopping the camera record the motion of the ball for each height.
- Save the video on your desktop.
Analyzing the video
To analyze the movie follow the steps shown in the screen cast below.
By analyzing the video use a graphical method to show that v2 = 2gh and find a value for g.
If this is used as an introduction to the practical programme and is not going to be assessed then the help pages can be used.
To help with writing a conclusion it might be interesting to try simulating this experiment. You will find instructions on how to do this here.
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