1. Feb 11, 2012

### -Physician

We know that
$F=ma$ or $F=ma=m \frac{v}{t}$, so the acceleration is rate of slowing or speeding velocity, then does force changes the momentum $p=mv$ or $p=Ft$.

2. Feb 11, 2012

### Staff: Mentor

What exactly is your question? Yes, a net force on a body does change its momentum.

3. Feb 11, 2012

### -Physician

4. Feb 12, 2012

### zoobyshoe

Doc Al, the correct expression of this would be FΔt = Δp, no? Ft = p strikes me as imprecise, confusing Δp with p, which is mv. In other words, we use FT or FΔt to find change in momentum, and mv to find momentum. Correct?

5. Feb 12, 2012

### Fatemeh_Az

i have another question , why we couldn't gather first law from second law ? and does 2nd law have any prove ?

6. Feb 12, 2012

### harrylin

Yes, I already pointed that out yesterday:

7. Feb 12, 2012

### Staff: Mentor

Right. Sure, his statements were inaccurate. But first I wanted to find out what his question was, as it wasn't clear to me just what he was trying to do.

8. Feb 12, 2012

### zoobyshoe

Me either. I just wanted to clarify because I'm talking to another guy in another thread who seemed to think Ft = p, as opposed to Δp. Seeing it twice made me wonder if it was somehow acceptable in some way shape or form I wasn't aware of. Thanks.