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Physics Questions

"Momentum is conserved meaning the total momentum of the objects before the collision is equal to the total momentum of the objects after the collision"

Is this correct? ^^^

Reply 1

Lauren-x-

It depends what the question is asking, but yes that is factually true - as long as there are no external forces acting on the objects :smile:

Reply 2

Daydreamer3

Original post by Lauren-x-

It depends what the question is asking, but yes that is factually true - as long as there are no external forces acting on the objects :smile:

Can you explain further by what you mean by no external forces. Like what if there was an external force acting on it and what could this force be and do?

Reply 3

Lauren-x-

Original post by Daydreamer3

Can you explain further by what you mean by no external forces. Like what if there was an external force acting on it and what could this force be and do?

Do you learn about impulse? (sorry, I can't remember what comes up at GCSE).

For momentum to be conserved, the impulses before and after the collision must be equal but opposite in direction. (impulse = force * time). This is because impulse is equal to the change in momentum, so for the change in momentum to be = 0 (conserved), their impulses must be equal in magnitude, but in opposite directions.

For example, before two cars crash there will be air resistance acting on the 2 cars - this an external force. Because the velocities of the two cars change after the collision, their air resistance will also change and may not be the same values as before the collision. This difference in air resistance will produce a different resultant force on each car, which could be different to the resultant force on each car before the collision. This means that their impulses (F*t) may not be the same, so momentum is not conserved.

Sorry if that didn't make much sense :redface:

Reply 4

Daydreamer3

Original post by Lauren-x-

Ohh okay thank you! I kind of understand it better now but we dont learn about impulse in GCSE's but I still sort of get it. :smile:

If the resultant force changes, lets say it increases or decreases. What will happen to the change in momentum or momentum in general?

Reply 5

Lauren-x-

Original post by Daydreamer3

Ohh okay thank you! I kind of understand it better now but we dont learn about impulse in GCSE's but I still sort of get it. :smile:

If the resultant force changes, lets say it increases or decreases. What will happen to the change in momentum or momentum in general?

Ohh right, sorry!!

I just found this link which sums up the principle, though it's quite a long read.

It's quite hard to explain at GCSE level - I think it's more of a fact that you need to accept that's why it is, though it's good that you're curious! The changes and everything can be shown by this link, but as you can see it's very complicated and you don't need to understand all of this! :smile:

Reply 6

Mo H

Watch these two videos:

1) https://www.youtube.com/watch?v=7LtoE88UvZs

2) https://www.youtube.com/watch?v=-Y7NPTH7SWA

They should help you understand momentum and impulse better.

Reply 7

Daydreamer3

Original post by Lauren-x-

Thank you so much! :smile:

Its okay and I'm always curious because that's the way I learn for some reason aha

By the way if you're at college are you doing A level physics?

Reply 8

Lauren-x-

Original post by Daydreamer3

Thank you so much! :smile:

Its okay and I'm always curious because that's the way I learn for some reason aha

By the way if you're at college are you doing A level physics?

Yes, I'm at sixth form and currently doing A2. I do maths, further maths, physics and history! Are you planning on doing A Levels? :smile:

Reply 9

Daydreamer3

Original post by Lauren-x-

Yes, I'm at sixth form and currently doing A2. I do maths, further maths, physics and history! Are you planning on doing A Levels? :smile:

Yes, I am planning on taking Biology and Chemistry but am stuck on the third option. It may possibly be maths but I do highly enjoy physics but then I would not want to take all three sciences. How hard would you say A level maths is ? Is there a great different to GCSE maths?

Reply 10

Lauren-x-

A lot of core 1 (1st module in A Level maths) is an extension of A* topics at GCSE, so not overly hard. Core 2 introduces some brand new things which can be pretty hard to start with, though they get a bit better with practise. Maths will certainly help with the science subjects too, so taking them together will allow you to improve with the calculation questions in the sciences. Though I wouldn't recommend it if you don't get an A or A* at GCSE (or the equivalent, if you have the new number system) as it is quite a step up. Anybody who got a B at GCSE dropped it at my school, and now some people who got an A are struggling a little at A2. But if you're dedicated to it, and make sure you save enough time to do loads of past papers, it will be okay!!

If anything, I think physics is a bigger step up than maths is. You do build on GCSE knowledge for physics, but personally I find the questions much more difficult to answer - especially the wordy ones! (I'm usually okay at most of the calculations).