TO MEASURE ACCELERATION WITH LIGHT GATES AND A LINEAR AIR TRACK

APPARATUS

Air track, blower, two light gates, rider with card, dual timer, pulley, weights, metre stick.

METHOD

Set up the apparatus as in diagram, but without the weights attached to the rider.

Place the rider at the start of the air track. Switch on the blower.

Push it gently so that it goes through both light gates.

Since no weights were attached, it should move with constant velocity.

If, however, t₁, the time taken to go through the first light gate and t₂, the time taken to go through the second light gate, are not equal, adjust the tilt of the air track until they are.

Attach the weights and thread to the rider.

Place it at the start of the air track. Hold the rider. Switch on the blower.

Record t₁ and t₂. Record the length of the card l.

Record the distance, s, between the centres of the light gates.

Ensure that the rider passes through the second light gate before the weight strikes the ground.

Calculate the initial velocity, u, and the final velocity, v, from

.

Calculate the acceleration, a, from
.

SOURCES OF ERROR

• There may be some residual friction between the air track and the rider.
• The air track may not be horizontal, causing the force of gravity to either increase or decrease the acceleration of the rider.
• There may be parallax when reading s or l.

SOLUTIONS

• Give the air track a slight slope until a rider with no weights attached goes through both light gates in the same time.
• Raise or lower one end of the air track as required.
• Ensure that your line of sight is at right angles to the metre stick.