AIM: TO MEASURE THE ACCELERATION DUE TO GRAVITY BY FREE FALL.

APPARATUS

Ball bearing, release mechanism, retort stand and clamp, metal plate with shock sensor,

timer, metre stick.

(click here for a close up of the release mechanism and the metal plate)

METHOD

Set up the apparatus as in diagram.

Measure and record the distance s from the bottom of the ball bearing to the metal plate.

(Ensure that the metre stick is the right way around.)

Release the ball bearing. This starts the clock.

When the ball bearing strikes the plate the clock stops.

Record the time t on the clock. (Repeat this three times and take the minimum value for t as the clock sometimes starts too early.)

Graph t² against s. Draw a best straight line.

Find the slope, m, of the graph. Calculate a value for g using g = 2m.

SOURCES OF ERROR

• The release mechanism may start the clock too soon giving too high a value for t.
• There may be parallax when reading the metre stick.
• The distance s must be measured from the bottom of the ball bearing.
• The distance s may be so small that the percentage error of the metre stick is too high.

SOLUTIONS

• Take a number of readings for t and choose the minimum value.
• Ensure that your line of sight is at right angles to the metre stick.
• Measure the distance s from the bottom of the ball bearing.
• Choose large values of s.