- #1

- 39

- 0

Cos final momentum - initial momentum = change in momentum =impulse. So it will always be in the direction of the final velocity right?

- Thread starter tubworld
- Start date

- #1

- 39

- 0

Cos final momentum - initial momentum = change in momentum =impulse. So it will always be in the direction of the final velocity right?

- #2

- 145

- 0

Yup, you are correct.

- #3

- 39

- 0

thanx alot!

- #4

andrevdh

Homework Helper

- 2,128

- 116

- #5

HallsofIvy

Science Advisor

Homework Helper

- 41,833

- 956

Your statement "the impulse is in the final direction?" is, in general,

IF you are dealing with motion on a straight line and IF the impulse is enough to reverse the direction of motion then, yes, the impulse

Suppose you have an object moving along a line and you give it "hit" that slows it down to 1/2 its speed. In that case, the "final speed" is still in the same direction and

If you work in two or three directions, it's much more complicated. Imagine a pool ball bouncing off a cushion. The impulse is perpendicular to the cushion but neither the initial nor final speeds are in that direction.

The best thing to say is "impulse is change in momentum: subtract the two momenta." Since momentum is mass*velocity and mass has no direction, as far as the direction is concerned, subtract the initial velocity from the final velocity.

In the example you gave: inital velocity -ve, final velocity +ve, ve-(-ve)= +2ve. The impulse is in the + direction, the same as the final velocity. In the example I gave, initial velocity is ve, final velocity is (1/2)ve, impulse is (1/2)ve- ve= (-1/2)ve, opposite to the final velocity.

For the pool table example, take initial velocity vector to be (vx, -vy), final velocity (vx,+vy). The impulse is the difference of those vectors: (vx, vy)- (vx,-vy)= (vx-vx, vy+vy)= (0, vy), not in the direction of either initial or final velocity.

- #6

- 39

- 0

Oh! Thanx for the explanation! I really UNDERSTAND now from your examples given! Appreciated! :)

- Last Post

- Replies
- 17

- Views
- 13K

- Replies
- 8

- Views
- 7K

- Last Post

- Replies
- 9

- Views
- 8K

- Replies
- 1

- Views
- 942

- Last Post

- Replies
- 4

- Views
- 1K

- Last Post

- Replies
- 2

- Views
- 3K

- Replies
- 1

- Views
- 2K

- Replies
- 2

- Views
- 1K

- Replies
- 7

- Views
- 471

- Replies
- 4

- Views
- 2K