B1K Music asked in Science & MathematicsPhysics · 7 years ago

# Physics/Gravity question.?

I had to explain gravity to someone, and that actually got me thinking of something pretty interesting.

We all know that gravity is the tendency of two objects with non-zero mass to accelerate towards each other, and that the greater mass an object has, the less it accelerates in comparison to other objects. Two Apples in zero gravity will "meet halfway", and the same is true for Earth and a falling object: Earth will move towards the object, but in such a minuscule amount it is virtually undetectable.

So the question is: if everyone on the northern hemisphere of Earth jumped over and over again, how long would it take for a noticeable shift in Earth's position relative to it's original position, (i.e. for Earth to move in our direction enough to be noticeable via observation), considering the massive difference in mass between us and the Earth, and assuming that the Earth is not revolving around the sun, but is isolated from any other celestial body?

Update:

Bridget: Clearly you do not understand how gravity works. I explained that Earth does accelerate, but in a very minuscule amount. I was asking how long it would take for a noticeable movement (assuming no other variables/stupid technical sh!t like "how would they survive with no sun" [which I'm sure someone will answer with]), NOT EVEN that the acceleration would increase; I never said that--it goes without saying that each time everyone jumps, the earth would accelerate towards them, but not keep its momentum. The question is simply a factor of how long it would take for a noticeable shift to finally take place. Please gtfo if you don't know what you're talking about.

Update 2:

Matt: You also seem to be oblivious to the mechanics of gravity, the Earth does accelerate when you jump, just by a very small amount, the number is not 0. No stupid/ignorant answers pl0x.

Update 3:

Matt: Also, you have the wrong idea of that law. The law of equal and opposite reactions describes what happens when, say, a car suddenly starts accelerating with you in it, or you decide to punch a wall really hard; the force will have an opposite reaction, effectively reflecting the shock (you get thrown back, the shock waves go into your arm and injure you), NOT that Earth will go towards, and then back away when you jump (seriously, that's just stupid). What you are implying is that when the Earth was forming, ever time a rock smashed into it, it bounced right back off, which is false (Nothing would have formed), the force of gravity outweighs the force of momentum, so your argument is terribly invalid.

Update 4:

Before the next answer: Answer the question with a time, but make sure you know how gravity works first, answers like "forever" won't work, forever is not a constant, forever describes the extent of human life expectancy, and I asked the question, including the exclusion of all other variables, therefore, human life is not a factor, just answer in how many years you think it would take FFS, like 1000 years, or 10 millenia, this isn't a realistic question, it is a theoretical question, so get your heads out of your asses and just answer the question.

Update 5:

Kevin: It's funny how I literally just said "no other variables"

Limited Energy is a variable, also what I described earlier as stupid technical sh!t.

You also have the wrong idea of gravity: the Earth is not a special object, it is an object with mass like everything else in the universe. What happens when you jump on a cheap plastic chair? it breaks. It doesn't bounce you back. What happens when you hit a cueball at an 8-ball? They bounce, and..oh look, they MOVE, and change from their original position. Same thing with Earth, in timed order since you don't seem to get it: You jump, now you are in position A. You now move towards the Earth, and the Earth moves towards you. However, the force of gravity is greater than the force of momentum; so when you and the Earth make contact, the momentum reflects, but the Earth made progress, being the object of greater mass, and has a positive net acceleration.

What, you think just because you are a "top contributo

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• 7 years ago

Gravity would pull on the earth the same way every time the population jumoed, it would not gradually pull more with each succeeding jump. Each jump would be an independent action/reaction.

• 7 years ago

Before you go acting big and tall Matt is right, the net momentum is zero. You are misunderstanding what he means by that. Since you have assumed Earth is not moving around the sun or in relation to anything, its original momentum as well as yours is 0. By the law of conservation of momentum the net momentum will then always be zero.

When you jump up, you will gain some momentum pointing up (obviously) and as you pushed off it, the earth will gain some momentum pointing down, equal to your momentum but opposite in direction. If that were the end of the story then yes, the earth would be moving but that's not the case. You soon find out that gravity will pull you back down, which will inevitably give you some downwards momentum. Again, the Earth feels the same, but opposite effect so it will eventually have some upward momentum equal and opposite to you. Then you will hit the ground in a perfectly inelastic collision and the ground will also hit you. The final momentum of the earth and of you will both be zero. Repeat until you have no energy to jump anymore.

During your entire Jump, the net momentum of the system was 0 just as it began. The Earth will not have moved AT ALL.

"force of gravity outweighs the force of momentum" First off momentum is not a force, it is a momentum. I think your point in that statement is the law of gravity outweighs the law of conservation of momentum, which is just wrong. The laws of physics work together, they don't "outweigh" each other. Also, nothing about momentum conservation implies that "when the Earth was forming, ever time a rock smashed into it, it bounced right back off". That would only be true if every collision was perfectly elastic, which none are.

Source(s): ma brain
• 3 years ago

Gravity won't be able to means some thing except the article is continually at a decrease aspect than what it replaced into earlier or you in straight forward words don't love it to offer up and there are not the different forces to offer up it (that is ridiculous). Gravity by technique of itself does no longer have any accessible means, you desire some thing else to placed issues in a larger floor contained in the first position... and the means "harvested" from that gravity is surely coming from that "some thing else", no gravity. So, a gravity powered motor vehicle will not in any respect ever artwork and any claims in the different case are hoaxes.

• 7 years ago

Forever, because the net momentum is zero and jumpimg will not alter this and change the position of the earth. (for every force there is an equal and opposite force)