ATAR Notes: Forum

VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: kenhung123 on June 07, 2010, 03:10:07 pm

Title: Still not very clear about this concept
Post by: kenhung123 on June 07, 2010, 03:10:07 pm: So when a question asks: What is the force/impulse exerted by A on B, do I calculate the impulse of A or B?

I surely matters because they are opposing directions.
Does this vary with different situations?
Title: Re: Still not very clear about this concept
Post by: dyaner on June 07, 2010, 03:22:09 pm: Good question...
Title: Re: Still not very clear about this concept
Post by: shokstar on June 07, 2010, 03:32:09 pm: Impulse equals change in momentum. When they ask for impulse of A on B, they ask for the change in momentum of B, therefore impulse of B.

Thats the way ive always thought of it.
Title: Re: Still not very clear about this concept
Post by: m@tty on June 07, 2010, 03:33:40 pm: Assuming that there are only two bodies, A and B, then the impulse by A on B is the change in momentum of B. It's like one guy is walking along(B) and then another guy(A) comes up and pushes him. The direction of the impulse is the same direction as the change in velocity. So in this example calculate the impulse of B.
Title: Re: Still not very clear about this concept
Post by: kenhung123 on June 07, 2010, 03:38:08 pm: Alrighty and to clarify: change in velocity=final-initial?
Title: Re: Still not very clear about this concept
Post by: m@tty on June 07, 2010, 03:38:39 pm: Yep.
Title: Re: Still not very clear about this concept
Post by: Chavi on June 07, 2010, 04:25:02 pm: Momentum is conserved, so Impulse is identical on all bodies.
Title: Re: Still not very clear about this concept
Post by: Greggler on June 07, 2010, 04:26:01 pm: they're one and the same thing.

impulse of a = impulse of b
Title: Re: Still not very clear about this concept
Post by: lachymm on June 07, 2010, 04:33:38 pm: EDITTED
Title: Re: Still not very clear about this concept
Post by: m@tty on June 07, 2010, 04:35:59 pm: Quote from: Greggler on June 07, 2010, 04:26:01 pm
they're one and the same thing.

impulse of a = impulse of b

Only in magnitude.

|impulse of a|=|impulse of b|

They are actually anti-parallel.

impulse of a = - impulse of b
Title: Re: Still not very clear about this concept
Post by: kyzoo on June 07, 2010, 05:53:34 pm: I think there was a question in CSE 2010 that directly examined this. And wow, I've never seen the word anti-parallel before xD
Title: Re: Still not very clear about this concept
Post by: m@tty on June 07, 2010, 05:54:19 pm: lol I learnt it from uni maths. :P
Title: Re: Still not very clear about this concept
Post by: Blakhitman on June 07, 2010, 06:05:38 pm: Change in anything is final-initial.
Title: Re: Still not very clear about this concept
Post by: TrueTears on June 07, 2010, 06:10:28 pm: Quote from: kenhung123 on June 07, 2010, 03:10:07 pm
So when a question asks: What is the force/impulse exerted by A on B, do I calculate the impulse of A or B?

I surely matters because they are opposing directions.
Does this vary with different situations?
$\mathbf{I} = \int_a^b \mathbf{F} dt$

where a is a point in time and b is another point in time, you can deduce what you need from this.
Title: Re: Still not very clear about this concept
Post by: kenhung123 on June 07, 2010, 07:11:56 pm: Quote from: TrueTears on June 07, 2010, 06:10:28 pm
Quote from: kenhung123 on June 07, 2010, 03:10:07 pm
So when a question asks: What is the force/impulse exerted by A on B, do I calculate the impulse of A or B?

I surely matters because they are opposing directions.
Does this vary with different situations?
$\mathbf{I} = \int_a^b \mathbf{F} dt$

where a is a point in time and b is another point in time, you can deduce what you need from this.
TT's attempt to simplify things....
Title: Re: Still not very clear about this concept
Post by: TrueTears on June 07, 2010, 07:17:29 pm: yup, the simplest form is always the best, u can pretty much derive everything from there, eg, F = dp/dt you can sub it in and do all kinds of things!
Title: Re: Still not very clear about this concept
Post by: ryan on June 07, 2010, 10:33:56 pm: Impulse suddenly made a lot more sense now!

Thanks TT!
Title: Re: Still not very clear about this concept
Post by: appianway on June 07, 2010, 10:38:02 pm: For the whole opposite direction of impulse thing, just remember that because of Newton's 3rd law, the forces are going to be opposite anyway, and impulse is defined as being in the direction of the force.
Title: Re: Still not very clear about this concept
Post by: olly_s15 on June 07, 2010, 11:03:04 pm: Quote from: kyzoo on June 07, 2010, 05:53:34 pm
I think there was a question in CSE 2010 that directly examined this. And wow, I've never seen the word anti-parallel before xD

it's part of NMR