# Impulse is change in momentum

#### aloshi

Hello!
yes is from Sweden and my English is not good, but will try to do as best as possible. My question is:
why can not consider the momentum as the acceleration energy?

I know that:
Impulse is change in momentum which is not the same as energy
Impulse can be expressed either as F * (delta) t or m * (delta) v since it is the same thing. That the expressions are as follows from Newton's 2nd Kraftlag together with the definition of acceleration: (delta) v / (delta) t

but as we move into the energy we see that energy is defined as:
W = mv ^ 2 / 2

if we compare the energy between, thus förendringen Middle two speeds we get that the change in energy is:
http://www.pluggakuten.se/wiki/image...itled11111.jpg [Broken]
I can not see a big difference between them, the only thing that separates them is that we have abbreviated removed (delta)stretch

but what is the difference between rörelsenergi and momentum:

I couple of things:
An important difference is that momentum is always kept in a collision between two or more objects. The kinetic energy conservation is generally not in a collision.
Another difference between kinetic energy and momentum is that kinetic energy is a scalar (ie, has size but not direction) while the momentum is a vector (ie, both the size and direction)

but I can not really understand what the difference between momentum and kinetic energy (accelerating energy)

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#### aloshi

Re: momentum

Hello!
yes is from Sweden and my English is not good, but will try to do as best as possible. My question is:
why can not consider the momentum as the acceleration energy?

I know that:
Impulse is change in momentum which is not the same as energy
Impulse can be expressed either as $$F \cdot \Delta t$$ or m * (delta) v since it is the same thing. That the expressions are as follows from Newton's 2nd Kraftlag together with the definition of acceleration: (delta) v / (delta) t

but as we move into the energy we see that energy is defined as:
W = mv ^ 2 / 2 $$mv ^ 2 / 2$$

if we compare the energy between, thus förendringen Middle two speeds we get that the change in energy is:
http://www.pluggakuten.se/wiki/image...itled11111.jpg [Broken]
I can not see a big difference between them, the only thing that separates them is that we have abbreviated removed (delta)stretch

but what is the difference between rörelsenergi and momentum:

I couple of things:
An important difference is that momentum is always kept in a collision between two or more objects. The kinetic energy conservation is generally not in a collision.
Another difference between kinetic energy and momentum is that kinetic energy is a scalar (ie, has size but not direction) while the momentum is a vector (ie, both the size and direction)

but I can not really understand what the difference between momentum and kinetic energy (accelerating energy)

Last edited by a moderator:

#### aloshi

Re: momentum

Hello!
yes is from Sweden and my English is not good, but will try to do as best as possible. My question is:
why can not consider the momentum as the acceleration energy?

I know that:
Impulse is change in momentum which is not the same as energy
Impulse can be expressed either as F * (delta) t or m * (delta) v since it is the same thing. That the expressions are as follows from Newton's 2nd Kraftlag together with the definition of acceleration: (delta) v / (delta) t

but as we move into the energy we see that energy is defined as:
W = mv ^ 2 / 2

if we compare the energy between, thus förendringen Middle two speeds we get that the change in energy is:
http://www.pluggakuten.se/wiki/image...itled11111.jpg [Broken]
I can not see a big difference between them, the only thing that separates them is that we have abbreviated removed (delta)stretch

but what is the difference between rörelsenergi and momentum:

I couple of things:
An important difference is that momentum is always kept in a collision between two or more objects. The kinetic energy conservation is generally not in a collision.
Another difference between kinetic energy and momentum is that kinetic energy is a scalar (ie, has size but not direction) while the momentum is a vector (ie, both the size and direction)

but I can not really understand what the difference between momentum and kinetic energy (accelerating energy)[/QUOTE]

Hello!
yes is from Sweden and my English is not good, but will try to do as best as possible. My question is:
why can not consider the momentum as the acceleration energy?

I know that:
Impulse is change in momentum which is not the same as energy
Impulse can be expressed either as $$F \cdot \Delta t$$ or $$m \cdot \Delta v$$ since it is the same thing. That the expressions are as follows from Newton's 2nd Kraftlag together with the definition of acceleration: (delta) v / (delta) t

but as we move into the energy we see that energy is defined as:
$$mv ^ 2 / 2$$

if we compare the energy between, thus förendringen Middle two speeds we get that the change in energy is:
http://www.pluggakuten.se/wiki/image...itled11111.jpg [Broken]
I can not see a big difference between them, the only thing that separates them is that we have abbreviated removed (delta)stretch

but what is the difference between rörelsenergi and momentum:

I couple of things:
An important difference is that momentum is always kept in a collision between two or more objects. The kinetic energy conservation is generally not in a collision.
Another difference between kinetic energy and momentum is that kinetic energy is a scalar (ie, has size but not direction) while the momentum is a vector (ie, both the size and direction)

but I can not really understand what the difference between momentum and kinetic energy (accelerating energy)

Last edited by a moderator:

#### tiny-tim

Homework Helper
Welcome to PF!

Hello! Hello! Hello! Welcome to PF!

I'm not sure what you mean by "acceleration energy" or "rörelsenergi", and your link isn't working, but anyway …

From the chain rule, d(mv)/dt = d(mv)/ds ds/dt = d(mv)/ds v = d(1/2 mv2)/ds.

Does that help?

#### aloshi

Re: Welcome to PF!

In order to acceleration, there must be a job. that is what I call the acceleration energy thus acceleration work. acceleration of work is $$F\cdot \Delta s$$ and this means increasing the kinetic energy. therefore increases speed.

http://img195.imageshack.us/img195/4176/40958030.jpg [Broken]

what I can not understand the difference between kinetic energy and momentum is not so great. we have only shortened away $$\Delta s$$[/QUOTE]

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#### aloshi

Re: momentum

This link shows how I have been derived momentum and nothing else-:
http://img195.imageshack.us/img195/4176/40958030.jpg [Broken]

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#### tiny-tim

Homework Helper
Hi aloshi!

(have a delta: ∆ and try using the X2 tag just above the Reply box )

I'll rewrite it so that it's easier to read …

If we have a very small increase in speed, from v to v + ∆v,

then ∆KE = 1/2 m ((v + ∆v)2 - v2) = mv ∆v = m ∆s/∆t ∆v = m ∆s (m∆v/∆t) = ∆s F,

which is the standard work-energy theorem, change in KE = work done by force F moving through distance s.

(I've used Newton's second law : impulse = force x time = change of momentum, or F ∆t = ∆(mv))​

Are you confusing impulse with work done ?

Impulse = force x time, but work done = force x distance.

Are you saying that for a very small change, distance is proportional to time, and so impulse is proportional to work done? If so, that ignores the fact that, if there is acceleration, distance is never proportional to time (except in circular motion, in which case the work done and the change in KE are zero).

#### aloshi

Re: momentum

i can't understand what is the difference between Newton's second law and the momentum?

#### tiny-tim

Homework Helper
i can't understand what is the difference between Newton's second law and the momentum?
Newton's second law : impulse = force x time = change in momentum

(or force = rate of change of momentum).

What is worrying you about that?

#### aloshi

Re: momentum

I can not understand the properties of momentum has. what is momentum?

#### tiny-tim

Homework Helper
I can not understand the properties of momentum has. what is momentum?
Momentum is mass times velocity.

It is the derivative of kinetic energy … mv = d/dt (1/2 mv2)

#### aloshi

Re: momentum

what is the difference physically, I understand the difference mathematical

#### tiny-tim

Homework Helper
momentum equals available "oomph"

Momentum is always conserved in collisions (while kinetic energy is not),

so momentum measures the "oomph" available when something hits something else.

#### aloshi

Re: momentum

I could not be pushed to the last:

"So the momentum measures the" oomph "available when something hits something else"
can you explain thanks

#### tiny-tim

Homework Helper
Momentum is a quantity which an object has when it moves.

It can transfer that quantity to another object.

That quantity is never lost, it only moves from one object to another.

It measures the ability to move another object …

the more momentum you have, the more you can move something else …

the less you have, the less you can move something else …

if you do move something else, you must give up some of your own momentum.

#### aloshi

Re: momentum

Requires no energy to give over part of their own speed?

#### tiny-tim

Homework Helper
Requires no energy to give over part of their own speed?
Change of energy is not required …

if you bounce a ball off a wall, there is no change of energy, but the ball exerts an impulse on the wall …

if the wall is on wheels, it will move, with little or no change in the energy of the ball.

What moves the wall is the change in momentum: the change in energy is irrelevant.

#### aloshi

Re: momentum

if we are dragging a ball from a height H. After the nozzles have the floor, it will not reach to the height H, but it will not be as high. it mean that we have lost energy?

if we are dragging a ball from a height H. After the nozzles have the floor, it will not reach to the height H, but it will not be as high. it does not mean that we have lost energy?
it can not mean that the floor gave a speed, and therefore its momentum. floor can not get a speed

#### tiny-tim

Homework Helper
if we are dragging a ball from a height H. After the nozzles have the floor, it will not reach to the height H, but it will not be as high. it does not mean that we have lost energy?
Yes, if we drop a ball from a height H (sorry, i have no idea what you mean by "nozzles" ), it will not quite return to height H because of the small amount of thermal energy (heat) generated.

But that energy creates heat (and/or vibration and noise), not movement.
it can not mean that the floor gave a speed, and therefore its momentum. floor can not get a speed
No, the floor does get a speed …

the floor is fixed to the Earth, and when the ball bounces up, the whole Earth moves very very very slightly down!

#### aloshi

Re: momentum

there are other ways of thinking that momentum? I want to understand it to 100%

#### tiny-tim

Homework Helper
there are other ways of thinking that momentum? I want to understand it to 100%
No, I think I've covered everything, but if you still have any questions, just ask.

#### aloshi

Re: momentum

No, I think I've covered everything, but if you still have any questions, just ask.
I do not know how to thank you, you have taught me much that my teachers could not teach me. I have that project and have chosen to investigate Compton scattering / Compton effect. Then I read about it, I saw that the momentum is the key element. so I've probably other issues that I need to ask. but it will be later, please respond during the Christmas holidays?

I will read more about momentum, therefore, I wondered if there was anything more that you can mention. thanks

#### tiny-tim

Homework Helper
I assume you're starting with http://en.wikipedia.org/wiki/Compton_scattering" [Broken]?

Remember that both momentum and energy are conserved in Compton scattering.

(In a collision, to solve the equations, you need both conservation of momentum and either conservation of energy or some physical constraint such as a fixed speed.)

On momentum itself, you might also like to read the PF Library article at https://www.physicsforums.com/library.php?do=view_item&itemid=183", and the Australian website referred to in it, about how conservation of momentum explains how a sound wave can be reflected from the open end of a pipe.

happy holidays!​

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#### aloshi

Re: momentum

Can there is more fuller on Compton scattered? Then other links

#### tiny-tim

Homework Helper

Can there is more fuller on Compton scattered? Then other links
Try a google book search …

on the google search page, type "Compton scattering" (including the quotation marks), then click on the drop-down menu marked "more" at the top of the page, and click on the first item, which is "Books" …

that will give you a lot of books on Compton scattering (for example, http://books.google.com/books?id=u7jIIpZrECAC&printsec=frontcover&dq="Compton+scattering"&client=safari&cd=1"), and any that are marked "Limited preview" can be read and downloaded free.

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