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To determine the acceleration of gravity in a free fall experiment.

Extracts from this document...




To determine the acceleration of gravity in a free fall experiment.



  • The experiment is carried out using the apparatus, as set up above.
  • The switch is used to open and close one circuit at a time.
  • The distance for the ball to fall is measured between the ball and the trapdoor with a ruler; a set square is used to see where the ball coincides with the ruler, making it a more accurate measurement.
  • Adjusting the height of the trapdoor can change the distance.
  • When circuit A is closed the power supply travels to the electromagnet, which magnetises the ball.
  • The timer is set to zero.
  • As the switch is moved, braking circuit A and closing circuit B, the power supply is cut off to the electromagnet and the ball falls.  The power supply now travels to the timer and timing commences.  The two actions happen simultaneously.
  • When the ball falls through the trapdoor the circuit is broken and timing stops as there is no power supply.
  • The time shown on the timer represents how long it took for the ball to reach the trapdoor.
  • The experiment is repeated several times at different heights, with 2 readings for each height.
  • Results are put into a table showing the distance, times, an average time and a time.
...read more.























The collected data will be presented graphically to find a value for gravity, this can be done by using an equation for constant acceleration, where

 x = displacement, u = initial velocity, a = acceleration, t = time

x = ut +  at²

It is assumed that there was no air resistance during the ball’s descent, therefore

a = g ,  the constant of gravitational acceleration.

The ball falls from rest so u = 0

The equation has been modified to now give

x =  gt²

This can be compared to the equation of a straight line graph, y = m x + c.

x = g  t²  + 0

           

y =  m  x  + c                              

Where  m = gradient of graph

              c = intercept

              y = vertical axis – displacement

              x = horizontal axis – time


...read more.


Air resistance could be a factor, but again, you would imagine the air resistance to be the same as the same ball is used for each reading.  If however, air resistance was occurring, a slightly different sized ball could used to repeat the experiment and see if it makes a difference.

One theory that could explain the differences in the results is retained magnetism.  When the power is cut off to the electromagnet, a small amount of magnetism is retained.  This is lost gradually over a very short period of time.  Thus holding the ball up for a very short amount of time, not enough to visually notice but perhaps enough to make a difference and cause a slight error.

        Another method for the experiment that would prevent some of these errors occurring is to use a multiflash photograph, which involves the use of a stroboscope.  The release of the ball triggers a camera to photograph the ball at each flash.

...read more.

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