EscapeGravity^{by DeepKids}

The ground pushing back. It is electromagnetic — the atoms in your shoe refusing to share space with the atoms in the floor. Nothing ever truly touches.

Air is a fluid, and shoving through it costs you. This — not gravity — is the only reason a feather loses a race to a stone.

Move a wing through air fast enough and the air pushes it upward. Birds, aeroplanes and a well-thrown frisbee all beat gravity with the same trick.

Push water out of the way and it shoves back with the weight of exactly what you moved. Float or sink comes down to that one comparison.

Not the same thing as mass. Weight is what gravity does to your mass, so it changes with where you stand. Your mass never does.

Force applied across distance. Every metre you climb is work done against gravity — which is precisely why stairs are tiring and lying down is not.

Travel sideways fast enough and the ground curves away as quickly as you fall toward it. That is an orbit: falling forever and always missing.

11.2 km per second from Earth’s surface. Hit that and you never come back down — no engine needed for the rest of the journey.

A force that ignores gravity completely. And not all metals feel it — iron, nickel and cobalt do; aluminium and copper simply don’t.

Bend something springy and it quietly stores your push. Let go and it hands the whole lot back — a catapult, a bow, a diving board.

The one force in the box you cannot touch. Every single thing humans built to leave the ground started as somebody working something out.

The single point gravity acts through. Keep it over your feet and you stand; let it wander past them and you are already falling.

Where opposing pulls cancel and you hang without falling — the same idea that makes a Lagrange point out in space actually work.

Fall all the way here and the Earth pulls you in every direction at once — so it cancels. You would be weightless at the exact centre. Crushed, but weightless.

Solid rock that flows like treacle over millions of years. And gravity doesn’t fade as you sink through it — it climbs, peaking right at the bottom of this layer.

The thin skin we live on — less than 1% of the way to the centre. Every hole humanity has ever dug is still inside this layer.

Where the race begins, at about 9.8 m/s². Climb from here and gravity fades away. Dig from here and it gets stronger first — before collapsing to nothing at the centre.

Where every cloud, storm and aeroplane lives. Three quarters of the atmosphere’s entire mass is squashed into this bottom layer alone.

Home of the ozone layer — and it gets warmer as you climb, not colder, because ozone up there is busy absorbing ultraviolet on your behalf.

The coldest place in the whole atmosphere, and where meteors burn up. Too thin to fly a plane in, too thick to hold an orbit in.

Thousands of degrees — and you would still feel freezing. The molecules are so far apart there is almost nothing there to hand you the heat. Auroras happen here.

Where the atmosphere gives up and quietly becomes space. An atom out here can travel hundreds of kilometres before it meets another one.

Not at the centre, and not at the surface either. It maxes out at the core–mantle boundary at about 10.7 m/s², then falls to exactly zero at the Earth’s centre, where every direction pulls equally.

Climb and gravity fades, but it never quite reaches zero anywhere. The Sun is still holding on to Neptune from four and a half billion kilometres away.

Astronauts float because they are falling, not because gravity ran out. Up at the ISS there is still roughly 90% of what you feel on your sofa.

Mass is how much of you there is, and it is the same everywhere in the universe. Weight is just a conversation between that mass and whichever planet you happen to be standing on.

Gravity varies slightly from place to place depending on how dense the rock beneath you is. Satellites have mapped the lumps — the planet is not a smooth ball of pull.

One locks you into a circle forever, the other lets you leave for good. The gap between the two is only a factor of about 1.4 — surprisingly little.

Five places where the Earth’s and the Sun’s pull balance so precisely that an object can just sit there. We put our best telescopes in them.

The Normal Force is electromagnetic. What your child feels as a solid floor is the repulsion between electrons refusing to let two lots of atoms occupy the same spot.

Heavier objects don’t just tug harder — they bend spacetime deeper. The well gets steeper, and climbing back out of it costs correspondingly more.

A hammer and a feather, dropped together with no air in the way, land together. Apollo 15 filmed exactly that in 1971, and you can still watch it.