Conservation of Energy Using a Simple Pendulum

Aim

To investigate the conservation of mechanical energy using a simple pendulum.

Learning Outcome

• Identify gravitational potential energy and kinetic energy.
• Explain the transfer of energy in a pendulum.
• Identify the equilibrium position.
• Explain how mechanical energy is conserved.
• Observe how energy changes from one form to another during motion.

Time Allocation

Approximately 45 to 60 minutes.

Apparatus

• Retort stand and clamp
• String
• Pendulum bob or metal mass
• Meter ruler
• Stopwatch, optional
• Marker or tape for position marking
• Protractor, optional

How Does It Work?

A pendulum continuously transfers energy between gravitational potential energy and kinetic energy.

Scientific Background

The law of conservation of energy states that energy cannot be created or destroyed, only transferred or converted from one form to another.

In a pendulum, gravitational potential energy is converted into kinetic energy, and kinetic energy is converted back into gravitational potential energy.

In an ideal pendulum system with negligible friction and air resistance, total mechanical energy remains constant.

Hypothesis

If a pendulum swings freely, then energy will continuously transfer between gravitational potential energy and kinetic energy while the total mechanical energy remains approximately constant.

Variables

Independent Variable

Height or starting position of the pendulum.

Dependent Variable

Speed and motion of the pendulum.

Control Variables

• Length of the string
• Mass of the pendulum bob
• Release angle
• Environmental conditions

Safety Precautions

Experiment: Investigating Energy Transfer in a Pendulum

Aim

To observe the transfer between gravitational potential energy and kinetic energy in a simple pendulum.

Method

1. Set up a pendulum using a string and pendulum bob attached to a retort stand.
2. Mark the equilibrium position directly below the suspension point.
3. Pull the pendulum bob to one side without stretching the string.
4. Hold the pendulum at a fixed height.
5. Release the pendulum without pushing it.
6. Observe the motion of the pendulum carefully.
7. Identify the highest points of the swing, the equilibrium position and where the pendulum moves fastest.
8. Allow the pendulum to continue swinging until the motion decreases.
9. Record all observations.

What Learners Should Observe

• The pendulum moves fastest at the equilibrium position.
• The pendulum slows down near the highest points.
• The pendulum stops momentarily at maximum height.
• Energy continuously transfers between gravitational potential energy and kinetic energy.
• The swing gradually becomes smaller over time.

Scientific Explanation

At the highest point of the swing, the pendulum has maximum gravitational potential energy and minimum kinetic energy.

At the equilibrium position, the pendulum has maximum kinetic energy and minimum gravitational potential energy.

As the pendulum moves downward, gravitational potential energy is converted into kinetic energy.

As the pendulum moves upward, kinetic energy is converted into gravitational potential energy.

Over time the pendulum slows down because some energy is transferred to the surroundings as thermal energy and sound energy.

Results Table

Position of Pendulum	Gravitational Potential Energy	Kinetic Energy	Observation
Highest point	Maximum	Minimum	Pendulum stops momentarily.
Equilibrium position	Minimum	Maximum	Pendulum moves fastest.
Swinging upward	Increasing	Decreasing	Pendulum slows down.

Optional Investigation: Effect of Release Height

Aim

To investigate how the starting height affects the motion of the pendulum.

Method

1. Release the pendulum from different heights.
2. Observe the speed at the equilibrium position.
3. Compare the motion for each release height.

What Learners Should Observe

• Greater speed at the equilibrium position when released from a greater height.
• Larger swings for greater starting heights.

Conclusion

Increasing the starting height increases the gravitational potential energy of the pendulum.

Important Terms

Term	Meaning
Equilibrium Position	The lowest point of the pendulum swing.
Gravitational Potential Energy	Energy due to height above the ground.
Kinetic Energy	Energy due to motion.
Mechanical Energy	The total of gravitational potential energy and kinetic energy.

Expected Results

• The pendulum moves fastest at the equilibrium position.
• The pendulum moves slowest at maximum height.
• Energy continuously transfers between gravitational potential energy and kinetic energy.
• The swing gradually decreases due to friction and air resistance.

Conclusion

Energy is continuously transferred between gravitational potential energy and kinetic energy during the motion of the pendulum.

The total mechanical energy remains approximately constant, although some energy is gradually transferred to the surroundings due to friction and air resistance.

Questions for Learners

1. What happens to the pendulum at the highest point?
2. Where is the pendulum moving fastest?
3. What is the equilibrium position?
4. What happens to gravitational potential energy as the pendulum swings downward?
5. What happens to kinetic energy as the pendulum swings upward?
6. Why does the pendulum eventually slow down?
7. What is meant by conservation of energy?
8. What is mechanical energy?
9. Why does the pendulum stop momentarily at maximum height?
10. What forms of energy are transferred to the surroundings?

Common Mistakes

• Pushing the pendulum instead of releasing it naturally.
• Using a loose or stretchy string.
• Releasing from different heights unintentionally.
• Confusing kinetic energy with gravitational potential energy.
• Forgetting that some energy is transferred to the surroundings.

Teacher Notes

• Use a large pendulum for better classroom visibility.
• Clearly mark the equilibrium position.
• Ask learners to identify where the pendulum moves fastest.
• Reinforce the relationship between height and speed.
• Introduce friction and air resistance only after learners understand the basic energy transfer.

Teacher Tip

Extension Activity

Ask learners to investigate the effect of string length on pendulum motion or compare energy transfer in pendulums and roller coasters.

Real-World Application

Pendulums are used in clocks, seismographs, playground swings, amusement rides and scientific measuring instruments.

The conservation of energy applies to many real-world systems involving motion.