Does momentum "get transferred" during collisions?

justme · May 20th 2018, 03:12 AM

Is it correct to talk about momentum being transferred between objects during collisions? Did classical physicists view it this way at all?
I have heard the expression before and as a physics educator I want to make sure I am using the right language.
By describing momentum this way it seems to be modelling momentum as a "thing" that can be transferred or flow around a system, like "energy" being transferred. And that fact that it is conserved during collisions makes this language even more tempting to me.
However I have also heard that is not right to think of it this way at all, it is far better to just restrict its description to being a mathematical quantity (mv).

oz93666 · May 20th 2018, 03:45 AM

Well it is 'transferred' ... when a moving billiard ball hits another stationary one , some momentum passes over , is transferred ... this is a correct description of what is taking place ...

Mathematics has no place in describing what is happening , only in quantitative analysis ....IMHO

justme · May 20th 2018, 04:06 AM

ok...so if it is a "thing" that is transferred, what is a description of its properties? I can only describe it as mv...any other words or descriptions I find inaccurate eg an "indicator" of the ability to stop an object..but that description fits kinetic energy much better I feel.

studiot · May 20th 2018, 05:06 AM

Originally Posted by justme

Is it correct to talk about momentum being transferred between objects during collisions? Did classical physicists view it this way at all?
I have heard the expression before and as a physics educator I want to make sure I am using the right language.
By describing momentum this way it seems to be modelling momentum as a "thing" that can be transferred or flow around a system, like "energy" being transferred. And that fact that it is conserved during collisions makes this language even more tempting to me.
However I have also heard that is not right to think of it this way at all, it is far better to just restrict its description to being a mathematical quantity (mv).

I am very happy to discuss this, (and it leads to some deep Philosophy of Physics( but what sort of Physics are you a 'trainer' of, that you don't already have the answer?

Yes there was a time, before the word energy was invented, when one of the known types of energy was thought of as a substance, called caloric.
This view was later discredited.

Energy and momentum are properties of matter or substance, but they are not substances themselves.

But unlike mass, which is another property, you cannot 'transfer' a quantity of this property from one system to another.

Mass is a property that cannot be taken away from a body.

As to conservation laws it can be difficult to explain to beginners whether to use conservation of energy or conservation of momentum.
Iam am sorry to disillusion you, Oz, but you need Mathematics for this purpose.

Consider the following:

A rifle bullet of mass 0.1kg is fired at block of wood, of mass 1kg and situated on a long frictionless surface. The bullet impacts at 440m/s.
The impact embeds the bullet in the block and the two speed off at what velocity?

What is the kinetic energy before and after the impact?

Pmb · May 20th 2018, 10:42 AM

Originally Posted by justme

Is it correct to talk about momentum being transferred between objects during collisions? Did classical physicists view it this way at all?
I have heard the expression before and as a physics educator I want to make sure I am using the right language.
By describing momentum this way it seems to be modelling momentum as a "thing" that can be transferred or flow around a system, like "energy" being transferred. And that fact that it is conserved during collisions makes this language even more tempting to me.
However I have also heard that is not right to think of it this way at all, it is far better to just restrict its description to being a mathematical quantity (mv).

Yes. I can be transferred during collisions.

By the way. Energy is not a "thing." I.e. there's no such thing as energy.

For more on this please see: What is Energy?

Entire papers and books have been written on this subject. Think of energy in the same way an accountant think so money. Most of the money in the US is iomn computers recorded using 1's and 0's.

justme · May 20th 2018, 04:07 PM

Ok so there is no such thing as mass, energy or momentum..they are just "properties" of matter.
Can force be called a "property" of matter?
Can torque be called a "property" of matter?
Is matter a "thing"?

Thanks, I want to get the words right.

Pmb · May 20th 2018, 04:30 PM

Originally Posted by justme

Ok so there is no such thing as mass, energy or momentum..they are just "properties" of matter.
Can force be called a "property" of matter?
Can torque be called a "property" of matter?
Is matter a "thing"?

Thanks, I want to get the words right.

What is a bookkeepers property of matter? I explained that's all energy is, bookkeeping. Did you read what's in the link I posted? I didn't post it for me help or to impress women or buy me more beer.

justme · May 20th 2018, 04:56 PM

Originally Posted by Pmb

What is a bookkeepers property of matter? I explained that's all energy is, bookkeeping. Did you read what's in the link I posted? I didn't post it for me help or to impress women or buy me more beer.

Thank you. I read your link and I can see that energy can be called a property of matter and treated in a bookkeeping way.

Now I have 3 other related questions:
1) Can force be called a "property" of matter? If not then what would you call it?
2)Can torque be called a "property" of matter? If not then what would you call it?
3) Is there such a thing as matter?

justme · May 20th 2018, 06:11 PM

If energy does not exist and is a bookkeeping concept...why is it accurate for a physicist to describe energy as being absorbed?

....thats what my Oxford textbook on IB physics does.

Pmb · May 20th 2018, 06:14 PM

Originally Posted by justme

Thank you. I read your link and I can see that energy can be called a property of matter and treated in a bookkeeping way.

That never came from what I wrote. The most important think on that page is the quote from Richard Feynman from The Feynman Lectures on Physics, Vol I by Feynman, Leighton, and Sands, Addison Wesley, (1963)(1989). Section 4-1 What is energy? page 4-1

It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. However, there are formulas for calculating some numerical quantity, and we add it all together it gives “28” - always the same number. It is an abstract thing in that it does not tell us the mechanism or the reasons for the various formulas.

Originally Posted by justme

Now I have 3 other related questions:
1) Can force be called a "property" of matter? If not then what would you call it?
2)Can torque be called a "property" of matter? If not then what would you call it?
3) Is there such a thing as matter?

The answer to 1 and 2 are no. Matter is a poorly defined quantity in physics. That's why the best of them avoid it as much as I do. Its no better than the term "stuff." Is there such thing as stuff?

See: https://en.oxforddictionaries.com/definition/matter

Physical substance in general, as distinct from mind and spirit; (in physics) that which occupies space and possesses rest mass, especially as distinct from energy.

Some physicists, such as myself, think that's a poor definition.