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# Gravity!

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So, I'm in Gr. 12 University Physics with no prerequistes and I'm finding some difficulty with an assignment relating to gravity. I need to do well in this class as I have been offered a scholarship but missing the Gr.11 U Physics has made doing well in this class extremely difficult.

Anyways, the assignment requires that I consider a society where gravity does not exist. I have to figure out what would be the resultant and I need to know how I can compensate for it in order to sustain life. Here is what I got/questions:

-I figure that without gravity there is a possibility of bones decalcifying as a result of there being no weight bearing exercises. So, I thought that setting up spring systems such as the bow flex could possibly defer it. Is there any way I can express this in terms of physics?

- How would there be air resistance without gravity? If true, then if I jump I would never land as there is no opposing force; thus, Newtons First Law applies.

- Is it true that everything would be slow motion? If so, why in terms of physics would that be? Would a bullet be slower? I don't think it would change the momentum because momentum is a result of mass and velocity; thus the bullet would produce the same injuires. If no, then would everything be like free falling? If jumped up and then push off on say a ceiling would the force required to land be too overwhelming, potentially life threatening.

Anyways, I don't expect anyone to do calculations. All I am asking for is confirmation on some of my predictions and pointing in the right direction so i can make calculations. Thanks.

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hair would be a problem,,,everyone would have to wear hats or shaved heads. And going for a wee would be quite difficult.

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Right serious post. I can't answer your question but these are some other problems I thought there might be:

-Might there be problems with blood circulation? Surely there would be some effect.

-Muscles would become weaker I think.

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Strange assignment. There would indeed be air resistance, and nothing would be in slow motion.

I dont know why you would have to do this for a physics class, but just read some sci-fi. Put your society on a rotating habitat (like Halo, or ringworld, or your everyday rotating space station) to provide centrifugal force that keeps people pressed to the floor.

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You have to remember that there are still other forces going on as well, such as friction, etc. That means that in order to move something, you have to be able to apply a force greater than the force that the object has on it.

To be honest, if there was no gravity, I don't think planets the size of Earth would even exist, nor would they have atmospheres. A planet is formed because gravity holds all of that material together, including the atmosphere.

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Hmmm...the rotating habitat idea seems interesting only the math involved to demonstrate how this would balance everything seems too limiting in that this is a big assignment which i don't think would produce enough work to give me the mark I'm striving for. Also, I wouldn't really know how to show it. I know centripetal force is mv^2/r that is about it.

Why would everything not be in slow motion? I'm basing my predictions off Astronauts so I have no idea why this happens. Side thought - does earth have gravity because the world is spinning?

Gypsy Cake, I figured there be some medical problems associated with no gravity, which i'm hoping to overcome with spring systems. thanks.

PS - it is a strange assingment! It is like turning back on everything you were taught.

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The earth has gravity because it has mass. Spinning would have the opposite effect to gravity.

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;331667'']Put your society on a rotating habitat (like Halo, or ringworld, or your everyday rotating space station) to provide centrifugal force that keeps people pressed to the floor.

The CENTRIFUGAL FORCE does not exist!!

Sorry, it's a pet peeve.

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You have to remember that there are still other forces going on as well, such as friction, etc. That means that in order to move something, you have to be able to apply a force greater than the force that the object has on it.

To be honest, if there was no gravity, I don't think planets the size of Earth would even exist, nor would they have atmospheres. A planet is formed because gravity holds all of that material together, including the atmosphere.

Ya, I've come to know this but I think the task at hand is hypothetical. So, hypothetically what would people do to sustain life without gravity. What changes should be made? Sports? Walking? Flying? Its just to consider the possibilites without getting too technical...

So, in no gravity am I able to pick up a truck or is there some sort of friction present. I know if I were to push it friction would be in play but to actually lift there would be no force holding it down.. What would happen to Force Normal?

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The CENTRIFUGAL FORCE does not exist!!

Sorry, it's a pet peeve.

thanks....do you have any suggestions?

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So, in no gravity am I able to pick up a truck or is there some sort of friction present.
You still must overcome the inertia of the truck.

What would happen to Force Normal?

There isn't one without anything holding the object in place.

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You still must overcome the inertia of the truck.

There isn't one without anything holding the object in place.

So, how would i make calculations to prove that?

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I think if there was no gravity, "breathing" and "staying on the surface of the planet" would take priority over sports and picking up trucks for most people.

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Is it true that everything would be slow motion? If so, why in terms of physics would that be? Would a bullet be slower? I don't think it would change the momentum because momentum is a result of mass and velocity; thus the bullet would produce the same injuires.

For this bit, think about gravity as being acceleration towards the earth.

Things would not necessarily occur in "slow motion", but movements might behave differently because of the different accelerations involved. Your bullet is unlikely to change velocity to any appreciable degree, but it will be more accurate over short distances (because it is not "dropping" towards the ground) and wildly inaccurate over long distances (as in, flying away from the planet).

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I think if there was no gravity, "breathing" and "staying on the surface of the planet" would take priority over sports and picking up trucks for most people.

Surface?

Yourdad: the effect is still the same whether you call it centralpetal or fugal. It may be a psydo force but whatever is causing it (in this case the big metal thing accelerating) create an effect we collectively refer to by one of these names.

Let me make it clear I don't like this assignment I think it's silly. That said, a question I think you should consider. WHY would there be actions in slow motion?

Also have you read: http://en.wikipedia.org/wiki/Gravity ?

You can extend the spinning thing to work out how many levels you could have between say 10m/s/s and 8m/s/s fitted into a feasible space and how big the station would have to be etc....

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Surface?

It's made with one sheet of metal. They are a resourceful people.

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So, how would i make calculations to prove that?
F=ma
Surface?

Yourdad: the effect is still the same whether you call it centralpetal or fugal.

Err, no. The centripetal force(which exists) points inward, whereas the fictitious centrifugal force points outward.

It may be a psydo force but whatever is causing it (in this case the big metal thing accelerating) create an effect we collectively refer to by one of these names.
The effect which is referred to as the centrifugal force is caused by the tendency of an object to move in a straight line. A container happens to keep this from happening.

Ex. Water in a swinging bucket. The water is not drawn to the bottom of the bucket, but rather the corner.

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F=ma

Err, no. The centripetal force(which exists) points inward, whereas the fictitious centrifugal force points outward.

The effect which is referred to as the centrifugal force is caused by the tendency of an object to move in a straight line. A container happens to keep this from happening.

Ex. Water in a swinging bucket. The water is not drawn to the bottom of the bucket, but rather the corner.

It's just a difference in your coordinate setup in the maths. A - becomes a +. Centralpetal forces are just the name for whatever force is pulling inwards, in the case of sattellites it is gravity, a ball on a string being swung around it is the tension in the string...

Although my preference is for the use of petal not fugal. Because it removes the missconception of an outwards invisible pulling force, but if you're smart it doesn't matter.

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Thanks yourdad...is there anything I should consider? This is a big assignment and I cant think of things to do?

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Hmmm... if there is no gravational potential energy then is it safe to assume that there would be no kinetic energy. Also, on account of there being no gravity is it safe to also assume that we would be weightless such seen in space. I understand that space has gravity but as a result of the gravational fields they somewhow produce weightlessness and constant free failing.

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Why would we have no kinetic energy? 1/2 mv^2 has no gravity term in it. As long as you have some method of applying a force (change of mass is the most obviouse, throw something backwards) you would have KE. Yep you would be weightless.

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How would I determine that the force exerted by pushing off a wall would equal the force required to stop me ( i know it wouldn't exaclty equal but i figure it be close with there being no gravity). I'm trying to prove this in order to make-up a science fiction based game for the creativity component of the assigment. So, far I have determined that the velocity would obviously be constant and i have been trying to play around with magnitudes and impulses but I cannot figure out how I would calculate the force necessary to push myself off the wall. Anyways, any help would be very appreciated.

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