Mechanics
Newton's cradle
Watch momentum pass through the row to the far ball.
Simulate Newton's cradle collisions and conservation of momentum. Watch momentum transfer through a chain of balls and compare elastic collision outcomes with live measurements.
Newton's cradle
A row of equal balls transfers momentum through nearly elastic collisions — the far ball swings out while others barely move.
When the end ball strikes the row, momentum travels through the chain of contacts. In the ideal case the last ball leaves with most of the momentum while interior balls remain nearly stationary.
- Momentum conserved along the row
- Nearly elastic contacts
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
If you pull back the first ball to a release height h and let it swing into the row, what determines how fast the last ball flies out?
Predictions to weigh
- The far ball leaves with about the same speed the first ball had at impact.
- The far ball leaves slower, since the middle balls absorb some of the motion.
- The far ball leaves faster than the first ball's impact speed.
Variable roles
What you set:
- Ball mass (kg)
- Release height (m)
What you measure:
- Release PE (J)
- Far ball's exit speed (m/s)
How the investigation runs
- Open the Newton's Cradle preset in the sandbox.
- Drag the leftmost ball outward and up to set a release height, then read off how high it sits above its resting point.
- Release the ball and let it swing down into the row of touching balls. Watch which ball(s) fly out on the far side, and how high they swing.
Governing equation
Gravitational Potential Energy — PE = m·g·h
The pulled-back ball stores energy equal to its weight times how far you lifted it above its resting point — this is what powers the whole chain reaction once released.
Kinetic Energy — KE = ½·m·v²
As the released ball swings down, its stored PE converts to KE; at the bottom, that KE is what gets handed almost entirely to the far ball through the chain of collisions.
What the printable worksheet asks students to work out
- For each row, compute the release PE (mgh) and the impact KE the first ball should have just before it reaches the bottom of its swing (½mv², using your measured farSpeed for v). How do the two energies compare?
- Using conservation of momentum and kinetic energy for a chain of equal masses, explain why the far ball leaves with (approximately) the first ball's impact speed, while the balls in between barely move at all.
Where this shows up beyond the lab
- Why do the middle balls barely move, even though the impulse from the collision passes through every one of them?
- In the sandbox, does the far ball ever swing exactly as high as your release height? What does the gap (if any) tell you about how elastic the collisions really are?
- AP Physics 1 — Unit 4: Linear Momentum
- AP Physics C: Mechanics — Unit 4: Linear Momentum
- IB Physics — A.2 Forces and momentum
- General High School Physics — Momentum & collisions
- NGSS High School Physics — Conservation of momentum
- Middle School Physical Science — Newton's third law and collisions
- Welcome to Newtons Cradle
- Press Play
- Select the first ball
- Momentum down the row
- Open the data
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.