Is There Gravity in Space?

As a child I used to wonder why astronauts could float about in space. I imagined the higher you went the lighter you got. That’s how birds were able to fly I explained to myself. They flapped their wings to get off the ground and then floated as they got higher and higher.

This wasn’t an unreasonable explanation based on what I saw. I didn’t know about gravity. I couldn’t explain why things fell from the sky. But if I tried I may have suggested that as things got closer to Earth they got heavier and therefore they got faster as they dropped to the ground.

Gravity

The concept of gravity, and what it is, became clearer during my engineering degree at Glasgow University. Newton’s law of universal gravity explains there is a force of attraction between objects due to their mass. The more mass, the larger the force of attraction.

Professor Mac is standing on a grey platform with a red arrow showing the pull of Earth acting on him due to gravity
The gravity force of Earth on Professor Mac due to both having mass

The law also says that as the distance between the objects increases, the force of attraction reduces. Mathematically it is known as an inverse square relationship between the force of attraction and the distance between the objects. What this means is that the force reduces quickly as the distance between the objects increases. As the distance continues to increase, the force continues to reduce, at a slower and slower rate of reduction.

A graph shows the gravity force reducing rapidly as the distance between Earth and the object increases
The gravity force reduces as the distance between the objects increases

Astronauts floating or falling in space?

Professor Mac is shown floating in space with Earth in the background
It looks like Professor Mac is floating in space

So is this why astronauts float in space? Was I right as a child? Do spacemen lose all their weight since they are so far from the surface of Earth. Well as Professor Mac shows in his video on Newton’s Law of Universal Gravitation, this isn’t why astronauts float. Yes, they do lose some weight when high above the Earth’s surface, but not enough that they would start to float.

So what is going on? They look as if they are floating up there. Well the answer is that they are falling continuously to Earth’s surface. But they are also going very fast horizontally, so they keep falling past the edge of the Earth! The result is they circle the Earth in what we call an orbital motion. The reason they keep in an orbit and don’t fly off into space is that the gravity force on them keeps pulling them to Earth.

A space shuttle is in circular orbit around Earth with the gravity force between them shown by red arrows.
Professor Mac’s shuttle is in circular orbit around Earth

There is gravity in space

So there is gravity in space, and for astronauts in orbit around Earth it is similar to the level on Earth. Do you know how the astronauts achieve the horizontal speed they need to get into an orbit? Join Professor Mac as he answers this question in his video below.

Professor Mac explains how much gravity there is in space

Before you go!

Do you know, if you drop a large apple and a small apple from a tall building, which one will hit the ground first? Find out the answer in Professor Mac’s video.

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Mac

I teach physics and engineering through animation.

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1 Response

  1. Jeff says:

    This man deserves a Nobel piece prize.

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