. T.H. The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan Measurement of g, the acceleration due to gravity, using a free-fall apparatus.

. PDST Resources for Leaving Certificate Physics 2 Apparatus

. PDST Resources for Leaving Certificate Physics 3 Method  Set up the apparatus as in the photo.  Measure and record the distance s from the bottom of the ball bearing to the metal plate.  Release the ball bearing. This starts the scaler-timer.  When the ball bearing strikes the plate the scaler-timer stops.  Record the time t on the clock.

. PDST Resources for Leaving Certificate Physics 4 Here is a close-up of the release mechanism. Repeat the release of the ball bearing three times and take the minimum value for t as the clock sometimes starts too early.

. PDST Resources for Leaving Certificate Physics 5  Graph s against t 2.  Draw a best straight line.  Find the slope, m, of the graph.  Calculate a value for g using g = 2m. Note: We graph t 2 against s as the units of acceleration are m s -2, which makes it easier to remember how to draw a suitable graph.

. PDST Resources for Leaving Certificate Physics 6 Use the following table to draw a suitable graph and hence find a value for g.

. PDST Resources for Leaving Certificate Physics 7 Note: Don’t forget to draw a new table, with s in metres and t 2 in seconds squared.

. PDST Resources for Leaving Certificate Physics 8 Draw the best straight line and choose two non-data points.

. PDST Resources for Leaving Certificate Physics 9 Find the slope m and calculate g = 2m

. PDST Resources for Leaving Certificate Physics 10 This is reasonably close to the true value, g = 9.8 m s -2

. PDST Resources for Leaving Certificate Physics 11 Sources of Error  Take the readings from the metre stick at eye level to avoid the error of parallax.  The release mechanism may start the clock too soon giving too high a value for t. Take a number of readings for t and choose the minimum value.  The distance s must be measured from the bottom of the ball bearing to the top of the shock plate.