Coupled Resonant Pendulums: An Amazing Science Project to Explore Energy Transfer

Have you likely observed the back-and-forth movement of the playground swing?

Just imagine three weights swinging side by side. When you tug on something and let go, the motion travels to another piece after some time.

This may seem to be magic, but it is actually one of the science concepts, the power of resonance.

In this activity, you will see how energy moves from one pendulum to another without contact. Prepare to dive into the world of waves, vibrations, and energy transfer!

What you will learn in this Coupled Resonant Pendulums article?

• What Is a Pendulum?
• Energy transfer among objects.
• What does resonance mean?
• The way vibrations can move through a system.

Materials Needed for the Experiment

• 60 cm (2 ft) string
• PVC stand
• 2 jumbo paper clips
• Needlenose pliers
• 2 hex nuts (about 3/4 inch)
• Optional: PVC cutter or hacksaw

PVC Stand Parts (if using PVC):

• 2 × 12-inch PVC pipes
• 3 × 3-inch PVC pipes
• 2 × 90° elbows
• 1 × T-joint
• 1 × coupling

Steps for the activity

• Put together the PVC stand.
• String between Two Posts of the Stand
• Tie the string tightly between the two posts of the stand. 
• Use pliers to reshape the paperclips to make 2 hanger shapes.
• Ensure both hangers are almost equal in length.
• Hang the paper clips on the horizontal string.
• Put a hex nut on each paper clip hanger.
• Keep the two pendulums at a distance of 5-7 cm.
• Ensure that the two pendulums work independently and do not touch each other. 
• Your double pendulum is now ready for the experiment!

                             

What Should You Do?

• Gently move one pendulum to the side and let it go.
• Observe it oscillating back and forth.
• Take notice of the second pendulum it will slowly start to swing too!
• After some time, the first pendulum will slow down while the second pendulum oscillates higher.
• Before long, the first pendulum may nearly come to rest, and the second pendulum will swing all by itself.
• Continue watching. The motion will transfer back, causing the first pendulum to swing while the second comes to a stop.
• Notice just how the pendulums keep passing their energy backwards and forwards.

Give It a Shot!

• Use pendulum hangers of different lengths.
• Tighten or loosen your stick’s top string.
• Experiment with some heavier weights or some lighter ones.

Note how they alter the energy transfer between the pendulums.

Watch and Observe

The pendulums alternately swing back and forth due to the continuous transfer of energy by the connecting string.

Science behind pendulum  

• Every pendulum has its natural swinging speed, which is called the pendulum’s resonant frequency. Pendulums of the same length will swing at the same rate.
• The first pendulum starts swinging. It gently pulls on the string. This gives a push to the second pendulum. Because the pendulums are the length, these small pushes happen at just the right time. This causes the second pendulum to start swinging
• As the second pendulum gets energy, it starts to pull back on the first pendulum. The first pendulum slows down. The second pendulum swings higher.
• After a while, all the energy is in the second pendulum. Then things. The energy starts moving back to the first pendulum. The energy keeps moving forth between the pendulums. This continues until friction and air resistance slow down both pendulums. They stop.
• If the pendulums are not the same length, they will not swing at the same rate. This means the energy transfer will be weaker and the motion will look uneven. The pendulums will not swing together smoothly because the pendulums are lengths.

 

Conclusion

This activity is a way to see energy moving through a system.

When you watch pendulums share motion with each other, you can learn about resonance. Resonance is an idea used in music, engineering and many technologies. What looks like magic is really science working!

So build your pendulums, start swinging them and see energy move before your eyes!

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