Physics · Unit 4: Work, Energy & Power ·  Project 4-1-4

Pendulum Energy Swap

Let a pendulum go and track every joule: how much is still motion at the bottom, how much comes back as height, and where the rest quietly disappears  ·  3 class days

Starringmgh → ½mv² → mgh% = KE ÷ PE × 100
Unit 4: Work, Energy & Power

🔁 Review the Concepts

This project uses all three activities from this lesson. Skim whichever one feels shaky before you start.

Activity 4-1-1
Work & the Work-Energy Theorem
Why the string’s tension does zero work on the bob, and why gravity alone changes its speed.
Review activity →Deep dive →
Activity 4-1-2
Kinetic Energy
KE = ½mv² and the speed-squared rule. You’ll use it to turn your bottom speed into joules.
Review activity →Deep dive →
Activity 4-1-3
Gravitational Potential Energy
PE = mgh, choosing the bottom as zero height, and mgh = ½mv². Reread your “where did the missing energy go” notes.
Review activity →Deep dive →

🧭 Plot Summary

You can now count potential energy (mgh) and kinetic energy (½mv²). A swinging pendulum is the perfect test of both. At the top of the swing, the bob is all height and no speed. At the bottom it is all speed and no height. On the far side it climbs back up. If energy were perfectly conserved in each handoff, the bob would return to exactly the height it started from.

It doesn’t. Your job is to find out how close it gets, and to say where the rest went. You’ll predict the bottom speed, measure it from slow-motion video, track the height the bob reaches on the far side, and then run a test that changes how much the air pushes back. By the end you’ll have an energy ledger that accounts for 100% of the energy at every point in the swing.

What you will do in this project

  • Build a one-meter pendulum and predict its bottom speed from its release height before measuring anything.
  • Measure the real bottom speed with slow-motion video, then the height the bob reaches on the far side.
  • Work out how much of the starting energy stayed kinetic, how much came back as height, and how much is unaccounted for.
  • Draw energy bar charts for the top, bottom, and far side of the swing.
  • Test where the missing energy went by changing how much the air pushes back on the bob.

Why it matters

Engineers don’t just ask how much energy a machine uses. They ask where it all ends up. This is your first real energy accounting, and the same skill you’ll need for Problem 4-3-1, where an emergency slide has to turn height into a safe exit speed.

✅ Self-Check Before You Roll On

Check off each item as you get there. These are not grades — they are your own signal.