Physics Practical

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Physics Practical

Aim:Investigate the factors which determine the damping of a compound

pendulum to find an equation that relates the amplitude of

oscillations to the factors chosen to investigate.

Compound Pendulum

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For a system to oscillate in simple harmonic motion there are 3

conditions which should be satisfied;

1. A mass that oscillates,

2. A central point where the mass is in equilibrium,

3. A restoring force which returns the mass to its central point.

The compound pendulum (shown above) clearly does oscillate with S.H.M

as there is a mass that oscillates (1) about an equilibrium point (2)

and a restoring force returning it to its central point (weight of the

mass / tension in ruler (3)).

In S.H.M, there is a constant interchange between kinetic and

potential energy. In the case of the compound pendulum the potential

energy is provided by the increase in gravitational potential energy

(mgDh) as the oscillations occur in a circular fashion taking the mass

higher above the ground at its maximum / minimum displacements. So in

an ideal situation (one where 100% of the DEp is converted to kinetic

energy) the oscillations should go on forever with constant maximum /

minimum amplitudes.

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However, we can see in our everyday lives, in such situations as a car

suspension system or a child on a swing, that this is not the case. As

time passes, the amplitude of the oscillations in a system will die

down. This phenomenon is known as damping.

Damping occurs because of resistive forces in the system (mostly

friction in the case of the compound pendulum). So to for this

investigation, I will need to consider all the possible factors which

could have an effect on the resistive forces in the system;

Mass attached to pendulum A larger mass on the pendulum will increase

the potential energy of the system thus increasing the speed of the

oscillations. If the system is oscillating faster then energy will be

lost more quickly.

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