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Why things fall down

Gravity and orbits · level 1, lesson 1 of 6

A question to start

Hold a spoon over the table and let go. It falls. Hold it higher and let go: it falls again. Try a sock, a toy car, a crayon. Has anything you let go of ever gone up instead?

Why does everything go the same way?

The idea

The Earth is pulling. It pulls on you, on the spoon, on the sock and on the air. The pull is called gravity. You cannot see it and you cannot switch it off, but you can feel it: when you hold a heavy bag, the tired feeling in your arm is you holding the bag up against gravity.

the Earth pulls

The pull always goes the same way: towards the ground. That is the way we call down. When nothing holds a thing up, gravity pulls it down, and it falls. A table, your hand or a shelf can hold things up; a floor holds you up. Take the hand away and the spoon falls.

Mars pulls too. So does the Moon, and so does the Sun. Every planet pulls things towards itself. On Mars a dropped spoon falls as well, just more slowly, because Mars pulls less hard.

Worked examples

1. The ball on the stairs. A ball sits on a step. Why does it not fall? The step holds it up. Push it off the edge, and nothing holds it any more, so it falls to the next step.

2. Water from a tap. Turn on a tap and the water goes down into the sink, never up to the ceiling. Gravity pulls water too.

3. A balloon. A party balloon filled with helium floats up. Is gravity off? No: the air around it is pushing it up harder than gravity pulls it down. Let the helium out and it falls like everything else. (You meet why in the Air and fluids topic.)

Try it

  1. Name three things in your room that are being held up. What holds each one up?
  2. Drop a sock and a shoe at the same time. Which way do they go?
  3. Why does a ball you roll off a table fall to the floor?
  4. Would a spoon fall on Mars?
Answers
  1. Many answers: a book on a shelf (the shelf), a lamp on a table (the table), a picture on the wall (a nail).
  2. Both go down, towards the floor.
  3. When it rolls past the edge, nothing holds it up any more, so gravity pulls it down.
  4. Yes. Mars pulls things too, just less hard than the Earth, so the spoon falls more slowly.

Common mistake

"Things fall because they are heavy." Light things fall too: a crayon, a leaf, a grain of sand. Everything falls when nothing holds it up, heavy or light. The next lesson tests which falls faster.

Where it leads