Grade 9 Science Experiment 2 – Pendulums and Springs – How does a pendulum clock keep time?


The purpose of this science fair project is to demonstrate the physics of pendulums and strings. Grandfather clocks use a pendulum to keep time. A pendulum consists of an item that hangs from a fixed point with a weight at the bottom of it called a “bob”. This hanging item and its bob are free to swing in a downward motion by the force of gravity followed by an outward and upward motion. The direction the pendulum and bob travels is due to its inertia when it is pulled back and released.

Inertia refers to the principle that when a body is in motion it stays in motion and when a body is at rest it stays at rest unless it is acted upon by an outside force. In this science fair project, the outside force occurs when you pull back and release the pendulum from varying heights and starting positions.


height at which you pull back and release a pendulum affects the amplitude and speed of the pendulum. The length of the pendulum and weight of the bob will affect the speed of the pendulum.


1. Height at which you release the pendulum
2. Length of the pendulum
3. Weight of the bob on the pendulum
4. Amplitude of the pendulum swing

Materials Needed:

Tongue depressor
Paper Clip
Edge of a desk or flat surface