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Force question

by mvan4310
Tags: force
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mvan4310
#1
Oct23-11, 09:07 PM
P: 22
Hello,

I understand that force is mass x acceleration. What I don't understand is why acceleration and not velocity. Can someone explain why exactly
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iceblits
#2
Oct23-11, 09:49 PM
P: 113
well mass times velocity is actually something else..known as momentum
and force is actually the rate of change of momentum..you could perhaps try and read Newton's own writing on the matter to see how it was developed..I don't really know how to prove it :'(
mvan4310
#3
Oct23-11, 09:52 PM
P: 22
Well that would explain it. My physics teacher never would explain why and he skipped momentum for some odd reason

iceblits
#4
Oct23-11, 09:53 PM
P: 113
Force question

You should get to momentum afterwards I think
mvan4310
#5
Oct23-11, 09:59 PM
P: 22
Ill dive into my college physics book when I have the chance. Thanks I appreciate the fast replies
AudioFlux
#6
Oct23-11, 11:39 PM
P: 58
Suppose you are travelling in an elevator in gravity free space. If the elevator is moving with a constant velocity, you wouldn't even know that you are moving. But if it is accelerating, you would know, because you will be exerting a force on the floor of the elevator.
mvan4310
#7
Oct23-11, 11:46 PM
P: 22
Well, I understand the acceleration aspect. Just wasnt sure why Force was mass by acceleration. Couldnt we say that an object traveling at a constant velocity that hits a motionless object imposes a force upon impact?
AudioFlux
#8
Oct24-11, 12:01 AM
P: 58
Quote Quote by mvan4310 View Post
Well, I understand the acceleration aspect. Just wasnt sure why Force was mass by acceleration. Couldnt we say that an object traveling at a constant velocity that hits a motionless object imposes a force upon impact?
Very true. That's because when the object moving with a constant velocity hits the motionless object, it decelerates and the motionless object accelerates from rest. Check this out: http://en.wikipedia.org/wiki/Impulse_(physics)
mvan4310
#9
Oct24-11, 12:32 AM
P: 22
Quote Quote by AudioFlux View Post
Very true. That's because when the object moving with a constant velocity hits the motionless object, it decelerates and the motionless object accelerates from rest. Check this out: http://en.wikipedia.org/wiki/Impulse_(physics)
Wow, its the simple things I seem to not think of.... Lol
russ_watters
#10
Oct24-11, 05:37 AM
Mentor
P: 22,282
Er - I wouldn't say that. Impulse is not force. A collision does not have one single force associated with it, so it is far too simplistic to associate force with velocity.
Naty1
#11
Oct24-11, 07:02 AM
P: 5,632
mvan: smart people have developed very exact definitions, such as force and momentum, acceleration and velocity, and refined them over many years...maybe even several thousand years. So no one should be surprised as they study that accumulated knowledge that it is not always obvious....especially at initial exposure.

Force is related to acceleration because a fixed unbalanced force acting on a mass causes a uniform acceleration, not a uniform velocity. A uniform velocity is associated with a fixed unbalanced force: zero.

One relationship between force and velocity: FT = MV
jetwaterluffy
#12
Oct24-11, 07:37 AM
P: 227
If you send something at a velocity, it will stay at the same speed if not exerted on by a force.
Sammy8
#13
Oct24-11, 09:02 AM
P: 4
This may be an off question, but what is Earth's movement classified as?

I'm guessing momentum: The sun being (mass x acceleration) creating the force (distance of mass). Then that force times the velocity of the mass to give our momentum.

Then you would basicly repeat this for the sun to the galaxy's center, and so on down to the center of space. Going from smallest body of mass to the largest.
Sammy8
#14
Oct24-11, 09:20 AM
P: 4
I guess the suns force wouldnt be times velocity because it doesnt go at a uninterupted pace. The solar systems force/mass must be impacted by another force to create that momentum.

Maybe an insight to anti-matter? It wouldnt be pushed out and compressed or anything. Since the mass of the solar system is accelerating and spreading out It would actualy be bringing more of the anti-matter/space closer to its core. In other words a displacement of mass and space, the distance between mass.

So the velocity would be the suns force constant rate of speed, then times the force of the anti-matter/space to equal our momentum.
jetwaterluffy
#15
Oct26-11, 03:22 AM
P: 227
The earth has an angular momentum whilst going around the sun, and the sun's force of gravity provides the Centripetal force.
Sefrez
#16
Oct26-11, 04:37 AM
P: 125
Quote Quote by russ_watters View Post
Er - I wouldn't say that. Impulse is not force. A collision does not have one single force associated with it, so it is far too simplistic to associate force with velocity.
Why not if a collision involves changing the sate of ones motion?
JHamm
#17
Oct26-11, 04:46 AM
P: 389
If you like you can say it is a result of Newton's first law, that stuff which is already moving is going to just keep moving that way unless something makes it change, so a force causes a change in velocity rather than velocity itself, but I think it's fair to say that the reason something will just keep on moving the way it is without a force is at the moment unknown.
jetwaterluffy
#18
Oct26-11, 05:00 AM
P: 227
Quote Quote by Sefrez View Post
Why not if a collision involves changing the state of ones motion?
Three reasons:
1) Impulse is not a force, it is a measure of change of momentum. Divide it by the time period it changes in, and you get the average net force.
2) Notice I said net force. The components of this force can be many different things.
3) Notice I said average force. In a collision, the net force often changes during the duration of the collision.


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