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Why does gravity pull us down and never up? – Gracie, age 9, Brookline, Massachusetts
Gravity is the explanation issues with mass or power are attracted to one another. It’s why apples fall towards the bottom and planets orbit stars.
Magnets appeal to some forms of metals, however they will additionally push different magnets away. So how come you’re feeling solely the pull of gravity?
In 1915, Albert Einstein found out the reply when he revealed his principle of normal relativity. The rationale gravity pulls you towards the bottom is that each one objects with mass, like our Earth, truly bend and curve the material of the universe, referred to as spacetime. That curvature is what you’re feeling as gravity.
Earlier than entering into the sophisticated world of gravity, it’s essential perceive spacetime.
Spacetime is precisely what it feels like: the three dimensions of house – size, width and peak – mixed with the fourth dimension – time. Utilizing some very sensible math, Einstein was the primary individual to understand that the legal guidelines of physics work in a universe the place house and time are merged collectively.
What this implies is that house and time are linked – if you happen to transfer actually quick via house, time slows down for you in comparison with somebody who’s transferring slowly. Because of this astronauts – who’re transferring very quick in house – age a tiny bit extra slowly than individuals on Earth.
Tokamak/WikimediaCommons, CC BY-SA
Matter makes gravity wells, not gravity hills
Bear in mind, gravity is the concept objects within the universe are attracted to one another as a result of spacetime is bent and curved. When Einstein got here up with normal relativity, he confirmed that each one stuff within the universe can curve spacetime – in physics phrases that stuff is mass and power.
MoMo Productions/Stone by way of Getty Pictures
Since your mind often thinks in regards to the world in three dimensions, it’s actually arduous to consider the 4 dimensions of spacetime as a single concept. So to make it simpler to visualise, think about the floor of a trampoline. If there’s nothing on it, it’s flat. However if you happen to stand on the trampoline, it stretches round your ft and creates a valley with you on the middle. If there’s a ball on the trampoline, it could roll towards your ft.
This can be a two-dimensional instance of how spacetime works. Your mass stretched the trampoline, creating what known as a gravity properly that the ball rolls into. That is similar to how the gravity of a heavy object – just like the Earth – pulls issues such as you and me towards it.
To make issues even weirder, since house and time are linked, time can be stretched by heavy objects!
The heavier you’re, the steeper the perimeters of the trampoline properly. That’s the reason actually large issues within the universe – just like the Solar or black holes – have stronger gravity than Earth.
So why does gravity pull you down and never push you away?
Think about somebody went underneath the trampoline and pushed up. The ball would roll away! This may be a gravity hill, not a gravity properly. So far as scientists know, matter – or stuff – all the time makes gravity wells and never gravity hills. Scientists can think about issues fabricated from unique matter or power that may trigger gravity to push you off into house, however up to now, nobody has discovered something that might trigger gravity to push you away from Earth.
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