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Measurement of g , the acceleration due to gravity, using a free-fall apparatus. Apparatus. 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.
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Measurement of g, the acceleration due to gravity, using a free-fall apparatus. The Professional Development Service for Teachers is funded by the Department of Education and Skills under the National Development Plan
Apparatus PDST Resources for Leaving Certificate Physics2
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 Physics3
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 Physics4
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 t2 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 Physics5
Use the following table to draw a suitable graph and hence find a value for g. PDST Resources for Leaving Certificate Physics6
Note: Don’t forget to draw a new table, with s in metres and t 2in seconds squared. PDST Resources for Leaving Certificate Physics7
Draw the best straight line and choose two non-data points. PDST Resources for Leaving Certificate Physics8
Find the slope m and calculate g = 2m PDST Resources for Leaving Certificate Physics9
This is reasonably close to the true value, g = 9.8 m s-2 PDST Resources for Leaving Certificate Physics10
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. PDST Resources for Leaving Certificate Physics11