Gravity for astronauts in orbit Why do astronauts appear weightless despite being near the Earth?
Gravity for astronauts in orbit
- When you look at a footage or photographs of astronauts in space,
- it doesn't look like there is any gravity at work here.
- everything is not falling down in one direction -- In fact it's not even clear what up or down is.
- everything just floats around...
- If I were to push off of this wall,
- I'll just float in that direction.
- So, it doesn't look like there is this overarching influence like gravity that is trying to pull everything down.
- But the question is that these astronauts are still not too far away from a super massive body.
- In fact the space shuttle gets up only a couple of hundred miles above the surface of the earth.
- So the space shuttle, if I was to draw it to scale, would probably be right about there.
- And we know, we know that the force of gravity between two objects is equal to
- big G, the gravitational constant times the mass of the first object, times the mass of the second object, over the distant between the two objects squared--
- And if the space shuttle is right here
- only a few hundred miles above the surface of the earth,
- This "r" isn't that different. It's a little further than if you were at the surface of the earth.
- Remember that "r" is measured from wherever you are, to the center of the earth.
- Or really "r" is the center of object to the center of earth. The center of the earth represents most of the distance here.
- So, if I am at surface of earth,or if I am at just the few hundred miles above the surface of the earth
- It's not going to change "r" that dramatically especially in turns of the percentage
- So when you look at this way
- it's seems pretty clear that the force of gravity for someone who is in space
- only a few hundred mile above the earth should not be that different than the force of the gravity for someone who is on the surface of the earth.
- So my question to you is what gives?
- If there should be gravity in space, how can we all these pictures of people floating around like this.
- And the answer is,is that there is gravity in space, and these people actually are falling
- they are just moving fast enough relative to the earth that they keep missing it.
- Let me show you what I am talking about there.
- So if I would take a, if I would,if I would
- let's see,I'm sitting here in Africa,and I would shoot something
- Maybe I have really good slingshot and I would sling something super fast at maybe a 45 degree angle.
- It might take off a little bit and eventually hit another point.
- and this is what I actually already be a super doppler slingshot.
- I just made travel a couple of thousands miles,at least over a thousand miles.
- If I make it go a little bit faster, if i put a little bit more force on
- if I just propell the projectile a little bit faster and might go litttle bit further.
- But it will eventually fall back to the earth.
- Let's try to propell it a little bit faster than that.
- Then it will still fall the earth.
- Let's propell it even faster than that,well, then it's still eventually going to fall to the earth.
- I think you might see where this is going.
- Let's go even faster than that.
- So if we go even faster than that,eventually it will fall to the earth,even faster than that.
- So if you, if you are throwing an object even faster than that,it would then go really far and then fall the earth.
- I think you see what's happening.
- Every time, you go faster and faster, you throw this projectile out faster and faster, gets further and further
- To some velocity that you release this projectile,and every time,whenever it's trying to fall to the earth
- it’s going so fast that it keeps missing the earth.
- So it will keep going around and around and around the earth. And a projectile like that would be in Orbit.
- So what happened is if there is no gravity for that projectile, if there is no gravity the projectile would just go straight away into the space.
- But because there is gravity it is constantly pulling it towards the center of the earth or the center of that projectile and the center of the earth would be pulled towards each other.
- I guess it’s a better way to think about it.
- The force gravity is doing that. And so its curving its path and if it’s going fast enough if the projectile whatever object we are talking about, it will just keep going around and around the earth
- And since there is almost pretty much for most of the surface, there is no air at if you go high enough especially like the space shuttle, like is no noticeable drag.
- This thing can just keep on going for a substantial amount of time.
- Although there is just a little bit drag, that’s why over time you do have satellites slow down. Because there is just a little bit air resistance, so the answer to this conundrum (difficult problem or question) is that there actually is gravity
- It’s not a gravity free environment, it’s just that the astronauts and space shuttle and everything else that’s in the space shuttle is all falling
- but it’s moving fast enough that it never hits the earth. It keeps missing the earth.
- it keeps going around and around and around.
- But, it is completely under the influence of the gravity
- if they were to just slow themselves down, if they were to just brake relative to the earth
- and if they were to just, you know, they put their brakes on right over there, they would all just plumit to the earth
- and there is nothing special about going three or four hundred miles up into space that all of the sudden the gravity disappears.
- The influence of gravity actually on some level just keeps going. You can’t.
- It might become noticeably small on some points but definitely only couples of hundreds miles up to the air, there is definitely gravity there.
- It’s just their in Orbit, they are going fast enough so if they just keep falling. They are never going to hit the earth.
- And if you want to simulate gravity and this is actually how NASA does the simulate gravity is that they would put people in the plane they called it the "Vomit Rocket" because it is known to make people sick.
- And they’ll make them go into a projectile motion. So if this is the ground in a projectile path or in a parabolic path, I should say.
- So the plane will take off and it will do a path exactly the same as something in free fall or in a parabolic path.
- So anyone who is sitting in that plane will experience free fall.
- So if you ever be in, if you ever you know right when you jump off, if you have ever bungee jumped or sky dived or
- Hum… even the feeling when a roller coster is going right over the top and it’s pulling you down and your stomach feels a little ill that feeling of free fall.
- That's the exact same feeling that these astronauts’ feel because they are in a constant state of free fall.
- But that is an indistinguishable feeling from if you were just in deep space and you weren't anywhere close to any noticeable mass
- that is an identical feeling that you would feel to having no gravitational force around you.
- So hopefully that clarifies things a little bit? To someone whos just sitting in the space shuttle and if they have no windows, there is no way of them knowing
- whether they are close to a mass of object or they are just in free fall around it, they are in orbit or
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