[nate95366]

With the school season rapidly approaching (too rapidly, it might be argued), I thought I would put the word out there for those of you who need to ask the occasional question or two or get some guidance on homework, especially in the area of science. I am a high school science teacher, so I hope that I can be of help to at least a few of you. You can either PM me or start a new thread. I try to stop by here regularly, but PM's show up in my email so I'll probably be quicker with those.

Nate

[Moon Boots]

I may well take you up on this offer eventually. I'm doing Chemistry and Physics A Levels (which is for 17-18 year olds, not sure of the US equivalent) and I'm bound to end up in a rut at some point.

You can look forward to some meaty questions on integration and logs later on in the year

[nate95366]

I like "meaty" questions. Bring 'em on!

Nate

[Moon Boots]

Oh just be patient, they'll come I'll get down to revision for my `Forces Fields and Energy` paper tommorow and find you an interesting question or two, no doubt.

Taking Advanced Physics without taking maths was probably the worst decision of my life

[Moon Boots]

I had my first proper Physics lesson today. We were learning about changes in momentum and how momentum is always conserved; we focused mainly on collisions.

My teacher mentioned `impulses`, he said that an impulse is a change in momentum. I think this is how to work out the change in momentum after two objects (A and B) collide with each other:

((initial velocity of object A * mass of object A) – (final velocity of object A * mass of object A)) + ((initial velocity of object B * mass of object B) – (final velocity of object B * mass of object B))


The lesson seemed relatively simple but I'm not hugely confident on the whole concept of an `impulse`, mainly because it sounds like a word like that should refer to something far more spectacular than a mere change in momentum.

I'm fairly sure that I've made a mountain out of a molehill, but what I'm really asking is whether or not my method above will provide me with an answer to a question regarding the change in momentum when two objects collide, and I'd also like confirmation on my teacher's defination of an impulse.

Thanks,

Jason

[nate95366]

Your teacher's definition is the correct one. Your math is unnecessarily complicated unless there is a possibility of each object gaining or losing mass during the collision.

((initial velocity of object A * mass of object A) – (final velocity of object A * mass of object A)) + ((initial velocity of object B * mass of object B) – (final velocity of object B * mass of object B))

I would put it this way:

Change in momentum (Impulse) of object A = mass of object A (final velocity A - initial velocity A)

Change in momentum (Impulse) of object B = mass of object B (final velocity B - initial velocity B)

Your addition of the two will simply give you the "total impulse" for the system.

Does that make sense?

Nate

[Moon Boots]

Ah, perfect. That will save me a lot of time when I come to do the end of chapter questions. This could become a very useful thread for a lot of people, if they choose to use it.

My teacher also said something along the lines of this today:

Originally Posted by Physics Teacher

Objects rarely come into contact with each other when they `collide`. Unless they are travelling at enormous speeds what actually happens is the electrons in the two surfaces start to repel each other once they get close and the two objects are repelled in opposite directions before they truly collide.

He said it in a much more eloquent way that I just did, and it was one of those moments in physics where something just clicks into place.