Optional Practical: Ball in a tube


In this practical the velocity of a ball falling in a tube will be measured to determine the acceleration due to gravity.


  • Arrange a length of tube and a ruler as shown in the diagram. You can either use clamp stands or stick it to the wall.
  • Place a photo gate so that the ball will pass through it just before it comes out of the tube. make sure that the sensor is lined up with the middle of the ball.
  • Connect the photo gate to the interface and set up the software so that you can record the velocity of the ball. Don't forget to enter the diameter of the ball.
  • Perform a trial run to make sure that everything is working. A magnet can be used to hold the ball at a specific height before it is released.

Research question

What is the relationship between the height of drop and the final velocity of the ball?

Independent variable: Height
Dependent variable: Velocity
Controlled variables: nature of tube, mass and radius of ball, position of sensor.


As the ball falls its PE is converted to KE. Applying the law of conservation of energy we get the equation:

mgh = ½mv2

This can be simplified to:

2gh = v2

By measuring the velocity of the ball as it is dropped from different heights use a graphical method to show that 2gh = v2 and determine the acceleration due to gravity, g.

New Ball in a tube

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