# 3.2.2 Investigating Motion & Collisions

### Investigating Motion & Collisions

• 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

#### 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

#### 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

#### 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

#### 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
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