Investigating Motion & Collisions (OCR A Level Physics)

• There are a number of techniques and procedures that can be used to investigate the motion of objects
• A few examples of experiments that could be carried out are:
  • Measurement of speed and acceleration of trolleys down a ramp
  • Collisions between trolleys on an air track to investigate momentum and energy changes
  • Determination of acceleration due to gravity, g
  • The terminal velocity of a falling object

• Typically, these experiments require the use of one or more of the following:
  • Trolleys
  • Air-Track Gliders
  • Ticker Timers
  • Light Gates
  • Data Loggers
  • Video Techniques

Trolleys

• Trolleys are essential when studying motion and collisions
• They can be used to investigate speed, acceleration, and momentum
• They are composed of
  • A light block of wood or plastic
  • Ball-bearing wheels (to reduce friction)
  • A spring-loaded plunger (for collisions)
  • A flat top surface to allow stacking or additional masses to be added

Trolleys are essential in physics experiments for speed, acceleration, and momentum

Air-Track Gliders

• This technique can also be used to investigate the conservation of momentum resulting from a collision
• Air tracks are the optimum equipment to use for this as they reduce the friction
• Hence the energy lost to overcoming friction is minimised and the collision is kept as elastic as possible

Air tracks are used to investigate collisions and the principle of conservation of momentum

Ticker Timers

• Another way of analysing motion in a physics lab is to use ticker tape
• A long tape is attached to a moving trolley and threaded through a device that places a tick upon the tape at regular intervals of time
• The ticker timer will produce a certain number of dots per second on the tape, which will travel at the same speed as the trolley
• The distance between dots and the time can then be used to determine the velocity

The distance between successive dots increases down the ramp shows that the acceleration of the trolley is constant

Light Gates

• Light gates provide the most accurate way of measuring the time taken for a trolley to move through a set distance
• A card is attached to the top of the trolley as this is will interrupt the light beams on the gates
• The trolley is released from the top of the ramp, with one light gate just in front of the release point and the other at the bottom of the ramp
• The time taken to travel between the light gates, t, can be used to work out the initial speed, u, and final speed, v
• The acceleration, a, can then be calculated using the equation:

v = u + at

Set up for investigating acceleration down a ramp using light gates

Data Loggers

• A data logger is an electronic device that records data and stores it for further analysis
• It can be set to record at regular time intervals or when triggered by a sensor, such as a light gate
• Data loggers are often used as a more accurate way of measuring time and eliminate the error from the human reflex speed needed to stop and start a stopwatch

Video Techniques

• Taking videos or successive photographs of objects in motion is a useful method for determining
  • The acceleration of freefall
  • Projectile motion
  • Terminal velocity

• This technique has two requirements:
  • The frames per second must be known, as this can be used to determine the time taken
  • The distance must be known, usually from placing a ruler in the shot with the object

Set up for investigating projectile motion using a camera