# How to Figure Out the Mass of Earth—With Balls and String

## It involves calculating some very, very tiny numbers in order to find some super huge big ones.

### Dot Physics, Forces

1/20/2022 10:35:00 PM

Before we had technology, the original method to calculate the mass of astronomical objects like Earth or the moon, was a stick and a string. Here's how this works:

It involves calculating some very, very tiny numbers in order to find some super huge big ones.

30. It's really cool, so I'm going to explain how it works.Let's go over this gravitational force model. First, the magnitude of this force depends on the product of the two masses interacting (m2we have better methods nowthe Greeks did a pretty nice job figuring this out

Let's start with a simple physics demo that you can try at home. Take a pencil and place it on the edge of a table so that about half of the pencil is hanging over the edge and it's almost about to fall over (but it doesn't). At this point, the pencil is mostly balancing right on the edge of the table. With only this tiny contact point supporting the pencil, the frictional force can't really exert any torque to stop it from rotating. Even a super tiny force pushing the end of the pencil will get it to rotate. Try a tiny puff of air from your mouth to get it to rotate.

Read more: WIRED »

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