Core Practical 10: Investigating Collisions using ICT (Edexcel A Level Physics)

Aims of the Experiment

• To investigate conservation of momentum in two directions
  • Considering if collisions are elastic
  • Constructing a diagram of 2D collisions
• Use of ICT software is required
  • 'Tracker' is recommended by Edexcel

Equipment List

• Small spheres
  • Of two different diameters (ball bearings are ideal)
• Digital camera able to record video
  • Support to allow it to be positioned directly above the collision
• Computer with Tracker installed
• 30 cm ruler
• Micrometer or calipers
• Balance
• Graph paper

Method

1. Measure the mass of the spheres using the balance and record

2. Measure the diameter of the spheres using a micrometer or Vernier calipers

3. Mark an approximately central point on the graph paper

• • This will be where the stationary sphere is placed

4. Start the camera recording

5. Within the area of the graph paper, roll a sphere into the stationary one

6. Replace the stationary sphere in its initial place and repeat the experiment up to three times

• • A slightly different angle of approach should be used for each collision

7. Download the video file from the camera to the computer that runs Tracker 

• • Load the clip into the program.

Analysing the Results

• Use Tracker to analyse the video clips.
  • Input the mass and diameter of each sphere when prompted
  • Use the ‘velocity overlay’ feature so that the software can analyse velocities
• The Tracker software allows for frame-by-frame analysis of the movement of the spheres
  • Orientate the axes to make the velocity of the moving ball along one of the axes
  • Record the momentum of each ball as indicated in Tracker

• Construct a vector diagram from the results

Evaluating the Experiment

• ICT is used in this experiment because
  • The events happen to swiftly for the unaided eye to take readings
  • ICT generally provides more precise and reliable data 

Systematic errors:

• Parallax error from camera to the table
• The precision of the balance may give a wide range of possible values for mass
  • If possible use a more precise balance
• The spheres may have damage
  • Check there is no damage to the surface of each sphere before using

• The Tracker axes may not be correctly aligned when analysing

Random errors:

• The collision event may happen between frames
• From variations in the table surface
  • This could cause loss or gain of kinetic energy due to friction or slopes
• The sphere may not travel far enough to hit the second stationary sphere
  • Discard this result and release with greater initial velocity