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Lesson 5: Fields

# Fields

Gravity, electric, and magnetic forces are non-contact forces that act over a distance, creating a field around an object. Fields extend through space and can be mapped around objects using a test charge that interacts with the field. These fields, which vary in strength and direction, help predict how objects will interact. For example, Earth's gravitational field pulls objects towards its center. Created by Khan Academy.

## Want to join the conversation?

• from what i learned i thought that the moon was going to float away but from what she said it will eventually crash into earth because of gravity? which one is it?
• The gravity bit is true, but the magnetic field surround the earth keeps the moon at a distance. As a result, it is being pushed away, but the gravity is keeping it on its orbit.
• If you have two magnets and move them closers until they touch, will the fields combine and become stronger? Thanks!
• No they will keep thier respective fields.
• Where can you go to escape all forces?
Just wanted to know, so I can go there and see what it's like.
• Space like out of earth
• Are there any other types of fields?
• there are gravitational electric electromagnetic magnetic and more
• At the video said that all objects with mass have a gravitational field. But I thought that, according to general relativity, there were no gravitational fields, and that different objects with mass are attracted to each other because of spacetime curving different ways.
• Massive objects warp spacetime, or curve it, as you said. Warped spacetime generates gravitational attraction. I hope that I answered your question.
• If this is so then how does a rocket stay in orbit around the earth?
(1 vote)
• tl;dr: it's gonna have to be FAST! Sideways fast. VERY very fast.

If the rocket is in orbit, then it has enough sideways motion that it doesn't fall to the earth, if you could stop its sideways motion it WILL fall down.

That's also how the moon doesn't crash on the earth. It IS falling towards the earth, but it's constantly moving fast enough to the side so it misses it all the time.

The International Space Station stays in space in the same way, but it's so close to earth that it actually feels some drag from the upper atmosphere, which slows them down and makes them lose some of that sideways motion and start falling down to earth, so every now and then they have to fire up their engines to give them more sideways motion and boost them up again.

Btw the space station is moving SO FAST that if it were to whizz by right in front of your eyes, you would NOT see it! It's going faster than a bullet! That's how fast it needs to go to stay that close to earth in orbit. If it orbited much farther away, it wouldn't need to move this fast, the moon for example is slower than the ISS cuz it's much farther away.

Numbers for the curious:
ISS orbits at 8km/SECOND! That's 28,800km/h!!
The moon orbits at 1km/s
A bullet can have a speed of about 0.8km/s
• What's the difference between field force and non-contact force?

I assume field force is any force that has field and non-contact force is any force that can be exerted without contact.
Then they are the same thing right? Or is there something other than field that can help exert force without contact?
• I don't really know as to why, but I'm willing to guess that a non-contact force is literally a force that doesn't require physical contact, and that fields are just another more specific subject related to non-contact forces; fields remain constantly around an object (up until a certain point, kind of like a boundary) and can include non-contact forces, soooo. maybe? probably just fields are just related to them/sub-sections

• vector from despicable me!
• I think you mean .