| Toolish |
04-03-2006 06:59 PM |
Quote:
Originally Posted by Mathew
I am very confused with the two. Velocity to me has always been pretty much completely interchangable with speed - is that correct ?
I have always seen it as the faster the speed and the more heavy the weight of an object hitting another object, the more it the second object moves. But with F=ma newtons second law, it confuses me....because it is not the velocity but the acceleration and like you said 'a constant velocity (speed I think...) means no acceleration which results in no force via the equation. If two rocks in space(just to get rid of other forces at the moment) are traveling at a speed or velocity but not accelerating, it appears to me that their should be force applied on to the other. Kinda like if you hit a cue ball in pool and its slowing down to a crawl where it seems to be deaccelerating, it will still give force to the object ball. Im just very confused and I know Im not right here but this is the way im thinking....where am I going wrong ?
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As others have said, velocity is speed with direction. So an object moving in a circle at constant speed will have a constantly changing velocity as the direction is changing. Think of a car driving a straight bit of road. If it drive 10mph along the road, then does a U turn and drives 10mph back down the road the speed has been the same both ways, but the velocities are the exact opposite of each other.
Use the two balls floating in space, towards each other. While they are floating (at a constant velocity) there is no force on either, hence no acceleration. Now, once these two balls collide with each other, as soon as they touch, they apply a force to each other, and therefore accelerate each other. This is where the F=ma comes into it. Throughout all collision there is energy conservation. That is the energy in the initial system will carry through to the final system. The initial system will have the kinetic energy (1/2 * mass * velocity^2) of both balls, during the collision some energy is given out as sound, the final system will then have the remaining energy still as kinetic energy of the 2 balls.
As another way to think of it. A ball sitting still in space weighing 100grams, and a block weighing 1kg approaches at 10m/s. Assume a perfect collision (no energy as noise, heat etc). Initial kinetic energy in the system is all in the block (.5 * 1 * 10^2 = 50 Joules). Assume during impact the collision causes the block speed to halve to 5m/s it now has energy of (.5 * 1 * 5^2 = 12.5 Joules), this leaves 50 - 12.5 = 37.5 joules of energy for the ball.
Using the KE=.5 * m * v^2,
37.5 = .5 *.1 * v^2
v = 27.4 m/s
Not sure how this helps a golf swing, but hope it helps with the physics you are trying to understand. |
