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** A pendulum is a hanging weight that swings back and forth, like the swing on a playground or the arm on a grandfather clock. These movements demonstrate physics in action, and this science fair project shows you how to make your own swinging pendulum! **

Pendulums are commonly used in clocks, but they also help in determining the acceleration of gravity. Because the acceleration of gravity varies by as much as 0.5% from place to place on Earth, precision pendulum clocks must be recalibrated after moving to a new location.

You can use a simple pendulum to determine the acceleration of gravity in your own area by measuring its period and calculating the value of g. The period of a pendulum depends on the length of its string, the mass of its bob, and the amplitude of its swings.

The amplitude of the swings in a simple pendulum is proportional to the tension T and the force of gravity, mg. This is why the amplitude of a pendulum’s swings increases as it gets longer, and why the amplitude decreases as the length of its string decreases.

There are many different kinds of pendulums, from simple gravity pendulums to those that use a spring to help a bob stay in motion. The simplest is the idealized mathematical model of a pendulum, a mass suspended by a cord of length L. This model is perfect for describing the motion of simple harmonic oscillators, because it has a predictable period of motion and no friction.

However, in reality, real pendulums are subject to friction and air drag, which cause their amplitudes to decrease. These effects cause the period of a pendulum to change slightly, so it’s important to keep the tension and the gravity constant for the same amount of time to get a good result.

#### How to Make a Pendulum for Physics

The first step is to make a simple pendulum by cutting a piece of dental floss or a piece of string about 1 meter long, and attaching a metal nut to the end of it. Set up the pendulum so that it swings in an angle of less than 10o, and then measure its period for ten oscillations using a stopwatch.

Repeat the process five times, and then calculate your average number of oscillations. You can also experiment with changing the weight of the nut to see how this affects the swing.

The period of a pendulum is (T=2pisqrtfracLg), where L is the string’s length and g is the acceleration due to gravity. A pendulum’s rate of movement only changes when the length of its string changes, so you can make a precision clock by adjusting the length of its string.