# Rube Goldberg Machine

A tabletop Rube Goldberg machine run by real physics: a rolling marble, toppling dominoes, a falling ball, a pulley and a bell\.

By PETE\!

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/h7AWHzGtiPBy)

## Transcript

### 1. A machine that takes the long way

This tabletop machine does one tiny job, ringing a bell, in the most roundabout way it can\. Each part gives the next one a push, like a message passed down a line of friends\. Every motion you will see follows real physics\.

Rube Goldberg \(1883–1970\) trained as an engineer and became a famous cartoonist, drawing silly machines just like this one\.

### 2. Gravity gets it rolling

A steel marble waits behind a little red gate at the top of a slope\. Lift the gate and gravity pulls the marble down the ramp, faster and faster\. Press the button to let it go\.

A rolling ball gains speed a little more slowly than a sliding block, because 2/7 of its motion energy goes into spinning\.

### 3. Dominoes pass the push along

The marble taps the first domino\. Each one tips over onto the next, so the push races down the line at about one metre per second\. Here it is in slow motion: every domino is a little bigger than the one before\.

A standing domino stores energy, like a set mousetrap\. One domino can topple another about 1\.5 times its size\.

### 4. A leap into the bucket

The last domino shoves a wooden ball off its little stand\. With nothing holding it up, the ball falls, gaining about 9\.8 metres per second of speed every second\. It lands in a tin bucket hanging on a string\.

In a fall, distance grows with the square of time: fall twice as long and you drop four times as far\.

### 5. The heavier side wins

The bucket hangs over a pulley, with a brass weight on the other side of the string\. With the ball inside, the bucket is heavier, so it sinks and lifts the weight\. When the bucket lands, the weight flies on and strikes the bell\. Ding\!

A pulley with a weight on each side is called an Atwood machine, after George Atwood, who described it in 1784\.

### 6. Where did the energy go?

Every stage began with something held up high: the marble, the tops of the dominoes, the ball\. Falling turns height into motion, and each bump hands some of it on\. The rest leaks away as sound and a little warmth, so every stage needs its own drop\.

That is why Rube Goldberg machines always work their way downhill, one stage at a time\.

### 7. Run the whole machine

Now watch it all at full speed, from gate to bell in under two seconds\. Press the button to reset the machine and run it again\. Drag the background to look at it from any side\.