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InvisibleDynoo
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Physics Problems. Help.
    #11263102 - 10/17/09 12:50 AM (8 years, 1 month ago)

Taking a college level physics course with no other physics background is not a good idea. I need some help, guys.

A man drops a bouncy ball ball from his hand to the floor.

1.
Now this is puzzling. . . when the ball is on the ground the potential energy is zero and certainly for an instant the kinetic energy must be zero because the ball has to stop for that instant to turn around. So if the potential energy is zero and the kinetic energy is zero. . . how does the energy return for another bounce? Where was the energy 'hiding?'


2. If it looks like some energy is lost upon each bounce. Where does it go?

Any sort of help is good. Math and physics were never my cup of tea....


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Offlineh00ligaN
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Re: Physics Problems. Help. [Re: Dynoo]
    #11263126 - 10/17/09 12:55 AM (8 years, 1 month ago)

does the ground absorb it?? i don't know.. i bet you wanted right answers, huh?


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InvisibleDynoo
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Re: Physics Problems. Help. [Re: h00ligaN]
    #11263144 - 10/17/09 12:58 AM (8 years, 1 month ago)

It bounces like a regular bouncy ball would.


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InvisibleThirdEyeOpening
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Re: Physics Problems. Help. [Re: Dynoo]
    #11263148 - 10/17/09 12:59 AM (8 years, 1 month ago)

The majority energy is stored in the elastic material of the ball.


When the ball strikes the ground, the energy is stored for a nanosecond, then released, some of the energy is lost in the form of heat, air friction, and some is absorbed by the ground.


EDIT: I should say all of the energy is lost in the form of heat, i haven't taken physics in a long time, but my memory is saying all friction crates heat.

Even the energy 'absorbed by the ground' is a heat energy from the ground contracting then expanding, releasing that energy as heat.


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Only two things are infinite, the universe and human stupidity. Im not too sure about the former.      -Einstein

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Edited by ThirdEyeOpening (10/17/09 01:10 AM)


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OfflineNeuron
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Re: Physics Problems. Help. [Re: ThirdEyeOpening]
    #11263285 - 10/17/09 01:31 AM (8 years, 1 month ago)



I approve this answer :thumbup:


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Edited by Neuron (10/17/09 01:32 AM)


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InvisibleUnholyChild666
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Re: Physics Problems. Help. [Re: Dynoo]
    #11263291 - 10/17/09 01:34 AM (8 years, 1 month ago)

man I haven't done any physics in 6 years I don't remember shit.


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InvisibleDynoo
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Re: Physics Problems. Help. [Re: ThirdEyeOpening]
    #11263294 - 10/17/09 01:34 AM (8 years, 1 month ago)

Thanks. I know the 3rd form of energy is heat, yet I wasn't sure if heat was the answer because we only covered potential and kinetic in class and because my mind hasn't grasped the concepts from this last lesson very well.


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Offlinedkamp18
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Re: Physics Problems. Help. [Re: Dynoo]
    #11263352 - 10/17/09 01:52 AM (8 years, 1 month ago)

the potential energy and kinetic energy are not at 0 at the same time. when the potential energy is at 0 the kinetic energy is at its highest.
when the kinetic energy reaches 0, when the ball hits the ground, the energy is stored as potential energy in an opposite direction, known on paper as a "vector"


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InvisibleDieCommie

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Re: Physics Problems. Help. [Re: dkamp18]
    #11263356 - 10/17/09 01:53 AM (8 years, 1 month ago)

hmm... I dont think energy is a vector.  Maybe you are thinking of the force.


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Offlinedkamp18
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Re: Physics Problems. Help. [Re: DieCommie]
    #11263360 - 10/17/09 01:56 AM (8 years, 1 month ago)

ya, that's how i meant it, that's why i said "on paper".

the direction of the energy, and the energy moving the ball(the force) are a vector.


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OfflineDeeGee
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Re: Physics Problems. Help. [Re: DieCommie]
    #11263374 - 10/17/09 02:01 AM (8 years, 1 month ago)

ThirdEyeOpening has the right answer for #2
For #1, upon contact with the ground, the kinetic energy of the falling ball is transferred to the materials of the ball itself as it is compressed by the normal force from the ground. The ball then de-compresses and in the process exerts force on the ground, forcing it upwards. Energy is lost in the process, which is why each bounce is smaller.


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Offlinedkamp18
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Re: Physics Problems. Help. [Re: dkamp18]
    #11263383 - 10/17/09 02:06 AM (8 years, 1 month ago)

Quote:

dkamp18 said:
the potential energy and kinetic energy are not at 0 at the same time. when the potential energy is at 0 the kinetic energy is at its highest.



and vice versa


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OfflineCapHat
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Re: Physics Problems. Help. [Re: dkamp18]
    #11263406 - 10/17/09 02:16 AM (8 years, 1 month ago)

So when we see the ball bounce back up almost to its original height, we know that it is always a little bit lower than it started because it has transformed some of that original potential energy to thermal energy.


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Offlinedkamp18
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Re: Physics Problems. Help. [Re: CapHat]
    #11263419 - 10/17/09 02:22 AM (8 years, 1 month ago)

Quote:

CapHat said:
So when we see the ball bounce back up almost to its original height, we know that it is always a little bit lower than it started because it has transformed some of that original potential energy to thermal energy.



exactly, there is always a transfer of some energy into heat.
sometimes even a transfer of energy into the opposing surface, that is why it wont bounce near as high on a carpet floor as on a tile floor.
there is more energy transferred and absorbed into the threads of the carpet, therefore less energy used in the ball for bouncing


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OfflinePhychotron
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Re: Physics Problems. Help. [Re: CapHat]
    #11263435 - 10/17/09 02:27 AM (8 years, 1 month ago)

it sounds like a translation problem.

when you drop a steel bar on a disc that is able to spin freely, it will start to rotate. the energy not lost has to go somewhere. In this case, it is stored in the ball as it expands outward and is flattened slightly.

but it also makes it seem more like a spring problem. what is the k value of the ball?


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On a mission to prove that the truth gets you no where.
They tried the truth, It didn't work. Then they wrote the bible. 

Only the foolish fear the inevitable.


Edited by Phychotron (10/17/09 02:32 AM)


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OfflineCapHat
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Re: Physics Problems. Help. [Re: Phychotron]
    #11263443 - 10/17/09 02:30 AM (8 years, 1 month ago)

FRICTION....dKamp18


Edited by CapHat (10/17/09 02:34 AM)


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OfflinePhychotron
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Re: Physics Problems. Help. [Re: Dynoo]
    #11263474 - 10/17/09 02:40 AM (8 years, 1 month ago)



--------------------
On a mission to prove that the truth gets you no where.
They tried the truth, It didn't work. Then they wrote the bible. 

Only the foolish fear the inevitable.


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Offlinedkamp18
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Re: Physics Problems. Help. [Re: CapHat]
    #11263504 - 10/17/09 02:51 AM (8 years, 1 month ago)

Quote:

CapHat said:
FRICTION....dKamp18



i might be misreading his problem, but i think that friction is really beyond the scope of his problem.

in most simple problems like that, external forces like air resistance and surface tension(or friction) are ignored.

i think we might be looking too much into it.

it seems it is more just a conceptual problem than anything,
the ball is dropped potential energy becomes 0 and kinetic energy is at its highest.
the ball hits the floor, some energy is lost as heat or absorbed into the opposing surface, potential energy is at its highest and kinetic energy at 0 for a moment.
the ball bounces back again releasing its potential energy again and bouncing back slightly lower than its original height

the only factor for friction would be in the elasticity of the material of the ball and the opposite surface


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OfflineCapHat
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Re: Physics Problems. Help. [Re: dkamp18]
    #11263537 - 10/17/09 02:59 AM (8 years, 1 month ago)

yea, but some potential energy loss turning to heat. I was talking about the heat not the transfer of energy. I was responding not to the original question. I know the energy get transferred, look at someone who got punched in the face or a car acceded like a rear end hit.


Edited by CapHat (10/17/09 03:02 AM)


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Offlinedkamp18
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Re: Physics Problems. Help. [Re: CapHat]
    #11263547 - 10/17/09 03:03 AM (8 years, 1 month ago)

o. ya we are on the same page then, i was just misreading. i wonder if the op actually got to a legible answer yet.


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