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# Acceleration

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for a completely closed AND ideal system you are right like I said in my previous message.

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Kedas, LOL, a new page already mate

were doing well Ive gotta hand it to Blike, he sure knows how to start off a good topic

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• 1 year later...
If I throw a ball straight up into the air' date=' is it still accelerating when its velocity is 0 (at the peak of its trajectory)?

I say yes...but I just want to be sure[/quote']

YOU ARE RIGHT

http://www.geocities.com/physics_all/index.html

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If I throw a ball straight up into the air' date=' is it still accelerating when its velocity is 0 (at the peak of its trajectory)?

I say yes...but I just want to be sure[/quote']

Well... if i tell u honestly.... the ball even upon reaching its peak( where its speed is relatively zero to us) it can be considered to be accelerating........

this is given by the principle of equivalence( of A.Einstein) .... which tells that every object within the space- time curvature can be considered to b accelerating.

so there 's ur answer man!

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it is accelerating. it's acceleration is -9.81m/s/s

edit: for future reference, don't use geocities as a rescource.

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• 3 weeks later...

I have a question that deals with acceleration but did not want to start a new thread as the question has probably already been addressed.

If there was a large hole that extended from the North Pole through the center of the Earth to the South Pole and a person fell in...would he fall all the way through or stop at the center? If he stops at the center would he move up and down like a bungie jumper until he comes to rest?

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I have a question that deals with acceleration but did not want to start a new thread as the question has probably already been addressed.

If there was a large hole that extended from the North Pole through the center of the Earth to the South Pole and a person fell in...would he fall all the way through or stop at the center? If he stops at the center would he move up and down like a bungie jumper until he comes to rest?

im guessing were assuming he survives things like pressure and heat and all that? he would pass though and start moving "up" on the other side untill the gravity slowed him enough to pull him back, like the bungie jumper. he would eventually stop due to friction with air.

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If you did it on the Moon, however, with no air friction, he would just keep going from one end to the other without stopping.

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last 2 posts are wrong. in the center (use a stone instead, it gets around the survivability probs) itll reach the middle , pass along it, be drawn back and eventualy reach equlibrium, with the graviation field, pulling equal in all directions.

it will have effectively acheived gravitational rest mass.

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how does that make my post wrong?

and actually, with no air resistance it wont. just like with no air resistance a ball thrown straight up(or up at all, it doesnt even need to be straight) will come back down at exactly the same speed.

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were talking the effects of gravity here, air resistance plays no significant part when falling to the center of a planet (Life Insurance may do though)

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last 2 posts are wrong. in the center (use a stone instead' date=' it gets around the survivability probs) itll reach the middle , pass along it, be drawn back and eventualy reach equlibrium, with the graviation field, pulling equal in all directions.

it will have effectively acheived gravitational rest mass.[/quote']

Say what?

In the middle gravity will not affect it at all, since it will balance out. As you get farther out from the core gravity slows you down until at the top you stop. Then you fall right back down again.

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were talking the effects of gravity here, air resistance plays no significant part when falling to the center of a planet (Life Insurance may do though)

air resistance is the only thing that makes it so he will eventually stop. air resistance creates this thing called terminal velocity, without which he would build enough speed on his plunge to overcome the gravity at the center and "fall" back up to exactly the same height again.

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Oscillate. Damped oscillation, in the presence of air.

Fg=-GMm/r2, but for a uniform density, M varies as r3, since only the enclosed volume of mass contributes to the pull (Gauss's law)

So you end up with something of the form F=-kx, which is Hooke's law, which applies to springs, etc. Simple harmonic motion.

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Oscillate. Damped oscillation' date=' in the presence of air.

F[sub']g[/sub]=-GMm/r2, but for a uniform density, M varies as r3, since only the enclosed volume of mass contributes to the pull (Gauss's law)

So you end up with something of the form F=-kx, which is Hooke's law, which applies to springs, etc. Simple harmonic motion.

super...

english?

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Assuming no friction, the person with fall back and forth forever taking the same time on each trip back and forth.

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Wouldn't some energy be lost due to gravitational waves?

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super...

english?

No, American. Why do you ask?

The person would always feel a restoring force toward the center, if they are not at the center. And the force gets larger as they move away. In the absence of friction, or other dissipative force, this means that they would oscillate back and forth.

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At the stop point the inertial forces and gravity cancel so there is no acceleration.

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Don't you mean there is no velocity. Acceleration would be constant in this.

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no, there would be no velocity at either end, there should be no acceleration for one instant in the middle, when no forces are acting on him, then his velocity carries him through and he starts accelerating back toward the center again.

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• 4 weeks later...

Just think it like this.

Though at the peak of its path its intstantaneous velocity is zero, take an elemental time after that. Its velocity will start to increase but in the opposite direction, since it is under the influence of gravitational acceleration g. So in effect, it still is accelerating at the peak, or else it would stay stationary there and not fall down, which you wil never see it happening like this.

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• 2 months later...

yes there is accelleration .....

Acceleration is continuous and constant.

just because a function has a maximum or minimum does not mean it stops there.

the object reaches 0 m/s for only and infinitly small amount of time... it does not hang there like jordan!

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acceleration is not continuous. there is no acceleration for one instant at the very bottom. it hits 0m/s at the peak(after falling back up), but it hits 0m/s/s at the very middle, when there is an equal gravitational force on all sides.

note that there are two situations in question here. the first post about throwing a ball straight up and the second question about falling through the center of the earth. just incase we are talking about different things here. im talking about falling through the middle.

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there is no acceleration for one instant at the very bottom.

Net acceleration anyway.

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