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Newtons Cradle

Short answer: Newton's cradle is a row of identical metal balls hung from a frame so they just touch. Lift and release one end ball, and after the collision the ball at the far end swings out while the middle ones stay almost still.

Pull two, and two swing out. The pattern follows from conservation of momentum and of kinetic energy in nearly elastic collisions: one ball leaving at the same speed is the outcome that satisfies both. Small losses to sound, heat and air resistance make the swings die down. The device is named after Isaac Newton, whose laws explain it, but it's credited to the 17th-century French scientist Edme Mariotte. The footage shows a classic desk cradle with five balls clicking back and forth.

VideoWrite-up1 sources

In collections:Everyday Physics

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What should you know about Newtons Cradle?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Releasing one ball sends one ball out the other end.

    DD-286-F01 · Write-up · Exhibit B (One in, one out)

  2. The cradle is credited to Edme Mariotte.

    DD-286-F02 · Write-up · Exhibit E (Named for Newton)

Video transcript: Newtons Cradle: Lift One Ball, and One Ball Answers

DID YOU KNOW? Newton's Cradle is a device that demonstrates the conservation of momentum and energy. It consists of a series of identically sized metal balls suspended in a straight line by wires. When one ball at the end is lifted and released it strikes the stationary balls transferring its momentum through the series. The ball at the opposite end then swings out with nearly the same speed as the first ball. This process repeats back and forth showcasing the principles of physics in action. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 21.4s Reel ·

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Newtons Cradle: Lift One Ball, and One Ball Answers Instagram Reel · · 21.4s

The write-up

Lift one ball, and one ball answers. It's named for Isaac Newton but credited to Edme Mariotte.

  1. Exhibit A

    Identical balls

    A row of identical metal balls hangs so each just touches the next.

  2. Exhibit B

    One in, one out

    Release one end ball, and one ball at the far end swings out.

  3. Exhibit C

    Two laws at once

    Momentum and kinetic energy are both conserved in nearly elastic collisions.

  4. Exhibit D

    Slowly fading

    Sound, heat and air resistance gradually drain the swings.

  5. Exhibit E

    Named for Newton

    The device is named after Isaac Newton but credited to Edme Mariotte.

Questions people ask about Newtons Cradle

How are the balls arranged?

They hang so each just touches the next.

Source: Write-up · Exhibit A (Identical balls) · Wikipedia: Newton's cradle

What happens when one end ball is released?

Two in gives two out.

Source: Write-up · Exhibit B (One in, one out) · Wikipedia: Newton's cradle

Which two quantities are conserved?

The collisions are nearly elastic.

Source: Write-up · Exhibit C (Two laws at once) · Wikipedia: Newton's cradle

Why do the swings die down?

Each click takes a little energy.

Source: Write-up · Exhibit D (Slowly fading) · Wikipedia: Newton's cradle

Who is credited with designing the device?

It's named after Newton anyway.

Source: Write-up · Exhibit E (Named for Newton) · Wikipedia: Newton's cradle

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. How are the balls arranged?

    1. Touching in a row
    2. Stacked vertically
    3. Spread far apart
    4. In a circle
    Show the answer

    Answer: A. Touching in a row They hang so each just touches the next. Source: Write-up · Exhibit A (Identical balls) · Wikipedia: Newton's cradle

  2. What happens when one end ball is released?

    1. One ball swings out the far end
    2. All balls swing
    3. Nothing moves
    4. The middle ball jumps
    Show the answer

    Answer: A. One ball swings out the far end Two in gives two out. Source: Write-up · Exhibit B (One in, one out) · Wikipedia: Newton's cradle

  3. Which two quantities are conserved?

    1. Momentum and kinetic energy
    2. Mass and color
    3. Heat and light
    4. Charge and spin
    Show the answer

    Answer: A. Momentum and kinetic energy The collisions are nearly elastic. Source: Write-up · Exhibit C (Two laws at once) · Wikipedia: Newton's cradle

  4. Why do the swings die down?

    1. Losses to sound, heat and air
    2. The balls get lighter
    3. Gravity weakens
    4. The wires stretch
    Show the answer

    Answer: A. Losses to sound, heat and air Each click takes a little energy. Source: Write-up · Exhibit D (Slowly fading) · Wikipedia: Newton's cradle

  5. Who is credited with designing the device?

    1. Edme Mariotte
    2. Isaac Newton
    3. Galileo
    4. Albert Einstein
    Show the answer

    Answer: A. Edme Mariotte It's named after Newton anyway. Source: Write-up · Exhibit E (Named for Newton) · Wikipedia: Newton's cradle

Cite this case file

Easterling, Marcus. "Newtons Cradle." The Detail Department (DetailEnjoyer), case file DD-286, last updated Aug 1, 2024. https://detailenjoyer.com/case/newtons-cradle/

Permalink: https://detailenjoyer.com/case/newtons-cradle/ · Last updated

Markdown version

Cite a single fact by its ID, for example DD-286-F01 → https://detailenjoyer.com/case/newtons-cradle/#DD-286-F01

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