Measuring Acceleration due to Gravity using a simple Pendulum.

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Measuring Acceleration due to Gravity using a simple Pendulum

Simple Harmonic Motion is very similar to the motion of a bob of a simple pendulum. A simple pendulum is made of a metallic bob suspended by fine string. Using these apparatus the acceleration due to gravity had to be measured. The acceleration due to gravity on earth is 9.81ms-2, therefore every second the particle will increase it’s speed by 9.81ms-1. Although, this may not be the case, due to air resistance.

Acceleration is directly proportional to force and acts towards a fixed position.


To derive a value for g, the S.H.M. equation was used:

For calculating ‘g’ the formula had to be rearranged:

T2 = 4π2 l



g = 4π2 l


Where: g is the acceleration to gravity; T is the period & l is the length.

Out of the above, the length of the pendulum had to be measured and then the period with that information. Instead of using the formula, a graph could be drawn of length against T
2, calculate the gradient, invert it then multiply by 4π

g =
4π2 l


“”””“””””.. all the weight is at the centre of the bob… - measuring to middle of bob. Keep bob small and dense is important….”””””

5b in analysis.. line of best fit – reason for lack of accuracy – strings got a weight therefore centre of gravity of whole pendulum will not be centre of bob.. Length of pendulum will be shorter than what measuring…”””””””””””

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To measure ‘g’ using simple harmonic motion the following apparatus were used:

  • Metre Rule
  • Metallic Bob
  • Fine string
  • Clamp stands & clamps
  • Split Cork (to hold string)
  • Digital stopwatch
  • Linear graph paper

They were set up in the following way:

The pendulum should have swung no further than 10° from the vertical.

The experiment was repeated three times to retrieve a more accurate result and twelve readings were recorded over 1.2m.

Preliminary ...

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