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Posted 02 December 2006 - 10:34 PM

which reaches the bottom of a slope faster, a ball rolling down the slope or a ball sliding down the sloap?

### #2ermd

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Posted 02 December 2006 - 10:54 PM

Depends on the friction.

If there is friction and it is the same in both cases, then rolling because less energy is lost as heat, sound etc. Whereas with sliding, more energy is lost. But if it is a ball, it can't slide if there is friction surely?

No?

### #3The Wedge Effect

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Posted 03 December 2006 - 12:17 AM

Erm...it's impossible for a ball to just slide down a slope. It'd eventually roll down the slope anyway. Don't think I've ever heard of a ball staying stationary and sliding down a slope. Sound an impossible feat to me.

### #4ermd

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Posted 03 December 2006 - 01:08 AM

Well, the only way it could happen is if the slope was frictionless. So it's a silly question, because both can't occur under the same circumstances.

### #5The Wedge Effect

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Posted 03 December 2006 - 11:32 AM

Even on a theoretically frictionless slope, the force of gravity would drag the ball down, and there is always one point on the ball that is slightly heavier than the rest of the ball, so it'd want to get down, and as it's a curved surface, it'd have to rotate, and thereby roll to get to the point, but when it get to that point, linear acceleration would be greater than the influence of gravity, so the ball won't be able to stop suddenly, so it'd continue to roll down the slope, despite the lack of friction. I think that if the slope was frictionless, it'd just make the ball slide and roll at the same time, as it can't just slide down a slope.

### #6linds

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Posted 03 December 2006 - 12:37 PM

A ball with wings FLYING down a slope.

### #7John

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Posted 03 December 2006 - 01:16 PM

QUOTE(The Wedge Effect @ Dec 3 2006, 11:32 AM)

Even on a theoretically frictionless slope, the force of gravity would drag the ball down, and there is always one point on the ball that is slightly heavier than the rest of the ball, so it'd want to get down, and as it's a curved surface, it'd have to rotate, and thereby roll to get to the point, but when it get to that point, linear acceleration would be greater than the influence of gravity, so the ball won't be able to stop suddenly, so it'd continue to roll down the slope, despite the lack of friction. I think that if the slope was frictionless, it'd just make the ball slide and roll at the same time, as it can't just slide down a slope.

That is the answer i was going to give lol

### #8The Wedge Effect

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Posted 03 December 2006 - 08:04 PM

University level physics FTW.

### #9John

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Posted 03 December 2006 - 10:05 PM

QUOTE(The Wedge Effect @ Dec 3 2006, 08:04 PM)

University level physics FTW.

I concur.

### #10Lesley

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Posted 03 December 2006 - 10:34 PM

Isn't a ball sliding down a hill the exact same thing as a ball rolling down a hill? How exactly does a ball slip?

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### #11broughy

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Posted 03 December 2006 - 10:55 PM

QUOTE(The Wedge Effect @ Dec 3 2006, 11:32 AM)

Even on a theoretically frictionless slope, the force of gravity would drag the ball down, and there is always one point on the ball that is slightly heavier than the rest of the ball, so it'd want to get down, and as it's a curved surface, it'd have to rotate, and thereby roll to get to the point, but when it get to that point, linear acceleration would be greater than the influence of gravity, so the ball won't be able to stop suddenly, so it'd continue to roll down the slope, despite the lack of friction. I think that if the slope was frictionless, it'd just make the ball slide and roll at the same time, as it can't just slide down a slope.

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### #12John

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Posted 03 December 2006 - 11:21 PM

QUOTE(lesley @ Dec 3 2006, 10:34 PM)

Isn't a ball sliding down a hill the exact same thing as a ball rolling down a hill? How exactly does a ball slip?

If the ball slid down the hill, only one point on the ball would touch the ground throughout the journey.

Where as a rolling ball would have multiple points of contact throughout the journey.

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Posted 04 December 2006 - 08:57 PM

naw wedge,its a fairly obvious assumption that the ball is a uniform sphere. its def that thy cant happen under the same circumstances. university level physics yer maw

### #14The Wedge Effect

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Posted 04 December 2006 - 10:30 PM

Yes, but even an uniform sphere would have imperfections. Nothing in life is perfect, and we all know it.

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Posted 05 December 2006 - 10:52 AM

actually mate in maths when you say 'uniform sphere' thats you saying it has no imperfections whatsoever

### #16John

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Posted 05 December 2006 - 10:56 AM

But this is physics, in physics we say that nothing is perfect.

### #17dondon

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Posted 05 December 2006 - 10:57 AM

I have one major question to ask

Why does it actually matter?

### #18John

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Posted 05 December 2006 - 11:05 AM

He's being a t**t, that's why it matters.

But to be honest it doesn't.

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Posted 05 December 2006 - 12:45 PM

ok so you're telling me that whenever in physics you're given a quaestion about a projectile you work it out with different centres of mass and so on assuming it irregular? or that when you're asked to work out g for a planet you take it as being irregular and not a point mass?didnt think so.

### #20John

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Posted 05 December 2006 - 01:06 PM

All calculations at Secondary level Physics, are approximations, as we do not use exact figures.

If we used exact figures, we would have to do infinite amount of calculations whenever using 'g' as at each point on the earth it differs ever so slightly, due to the earth, as you should know, not being perfectly smooth or spherical.

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