ok GCSE's today...i don't normally discuss questions after the test but this one seriously bugged me.

Ok this is to do with centripital forces. (easy stuff for some of you )

basically there's a ball on a string being swung around. The speed of the ball is said to be constant. HOWEVER, it is constantly accelerating, explain.
(Not exact wording but meh)

ok so i wrote because velocity is speed in a given direction, and the direction is constanty changing, the velocity is constantly changing therefore it is accelerating

I came out and i saw a boy who is cleverer than me and a teacher talking and they said it was wrong :S

HELP!
"Like a midget at a urinal, I was going to have to stay on my toes"

"Like a blind man at an orgy, I was going to have to feel my way through"

It is constantly accelerating towards the center. Acceleration is just the rate of change of velocity (its derivative). The speed is constant because speed is a scalar, but the velocity it constantly changing in direction, velocity is a vector.
Acceleration and Force vectors are perpendicular in centripetal motion. Although the magnitude of the acceleration might stay the same, the direction constantly changes. Therefore acceleration is never the "same."

EDIT: Whoops, meant to say velocity. Force and velocity are perpendicular...
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Last edited by darkstar2466 at Jun 11, 2008,
Um so do u think i got the marks for this question?
"Like a midget at a urinal, I was going to have to stay on my toes"

"Like a blind man at an orgy, I was going to have to feel my way through"

Speed is magnitude of velocity. Regardless of direction. It's changing direction --> changing velocity --> accelerating
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Yes I think you got it right. But knowing these exams you'll probably get 1 mark out of 2 or something like that.
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ok so i wrote because velocity is speed in a given direction, and the direction is constanty changing, the velocity is constantly changing therefore it is accelerating

I came out and i saw a boy who is cleverer than me and a teacher talking and they said it was wrong :S
Your answer is right. There are several ways this phenomena can be explained so it's likely the other guy put something that sounded like a different answer but in reality just said the same thing. I would expect you to get the marks.
The speed is constant because speed is just how fast it is moving. Speed has no direction (or else it'd be the velocity) and since the ball is moving at the same rate of speed, the speed is constant. But the acceleration is changing because the ball is changing direction (changes in direction mean there are changes in acceleration).
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