What effects the period of a pendulum?

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Alun Roberts

Physics Practical

What effects the period of a pendulum?

Aim

My aim is to investigate what effects the period of a pendulum.

Variables

The variables in this experiment are:

  1. The length of the pendulum.
  2. The size of the pendulum’s swing or displacement.
  3. The mass of the pendulum.
  4. The shape and air resistance of the pendulum.

Scientific Explanation

As the pendulum swings from its fixed point it contains energy and as it swings it goes through energy transfers. At the top of its swing the pendulum is for a moment still or stationary, at that point it has its maximum gravitational potential energy and has no kinetic energy. When the pendulum falls from the top of its swing its speed increases and is at it’s most at the bottom of the swing. Here it has its most kinetic energy and its least potential energy, as the pendulum rises to the top of its swing the speed decreases until it is stationary at the top again. Here it has no kinetic energy but has its most gravitational potential energy again. As the pendulum swings it loses energy as the shape of the pendulum causes ‘drag’ as it passes through the air, this is air resistance.

        

When the pendulum swings it has two forces acting on it. Gravity pulls the pendulum down but as it does this it is resisted by the tension of the string. These two forces can only be balanced when they are in opposite directions and this only happens when the pendulum is at the bottom of its swing. While the pendulum is not at the bottom of its swing these forces are unbalanced, this is what causes the pendulum to swing. When the forces are not opposite the pendulum is pulled one way by one force and the other way by the other force. Because of air resistance the force created by the tension in the string slowly decreases and this means that the force of gravity is slowly becoming greater than its opposing force and therefore the pendulum eventually slows down to a stop.

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Prediction

For this experiment I predict that the length of the pendulum will have a great affect on the length of time for a swing, in the way that the longer the pendulum is the longer the time for one swing. I also predict that the size of the pendulums swing will have no effect on the time. Also the mass of the pendulum will have no effect on the time per swing unless the pendulum is lighter than the string, if this is so the pendulum would not really swing and experiment would not really work.

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