Thread: acceleration (small question)

Acceleration simply means a change in speed, whether faster or slower.

Originally Posted by [SomeGuy]

Acceleration simply means a change in speed, whether faster or slower.

that has nothing to do with my question, i know what acceleration is.

what i want to know is, what is the relationship for a trolley's acceleration rolling down a slope depending on the slope angle. (oh, and assume the slope and trolley are frictionless)

Ok. If you tile the slope this way: \, it speeds up. Tilt it this way ---, it stays stationary. This way, /, speeds up.

The steeper the slope, the higher the velocity, the more acceleration.

I would draw the forces and build up from that. Newton's second law and all that.

Originally Posted by [SomeGuy]

Ok. If you tile the slope this way: \, it speeds up. Tilt it this way ---, it stays stationary. This way, /, speeds up.

The steeper the slope, the higher the velocity, the more acceleration.

Yes you basicaly just rewrote what i said i already knew. Im looking for all the jargon like the sine of the angle is directly proportional...

Originally Posted by Bonsay

I would draw the forces and build up from that. Newton's second law and all that.

Ah, good idea, ill do that later and see what i get. Thanks

Oh.

Okay, say the slope is at angle @ to the horizontal. There is a weight force of the trolley which acts vertically downwards, equal to Mg where M is the mass of the trolley. To find the component of this force in the direction of the slope, you need to multiply the force by sin@. Then to find the acceleration you divide this force by the mass of the trolley M, so a = Msin@g/M = gsin@.

As sin is strictly increasing between 0 and 90 degrees, increasing @ increases sin@ and hence the acceleration a = gsin@.

You may need to read up about Newton's second law and resolving forces if some of that is confusing.

Note that this ignores the frictional force. I can go into that if you want.

Originally Posted by [SomeGuy]

Ok. If you tile the slope this way: \, it speeds up. Tilt it this way ---, it stays stationary. This way, /, speeds up.

The steeper the slope, the higher the velocity, the more acceleration.

I think he already knows that

This should be your answer slash112

thanks guys, thats a massive help

thanks guys, thats a massive help

Originally Posted by slash112

thanks guys, thats a massive help

Originally Posted by slash112

thanks guys, thats a massive help

Double duplicates?

Haven't seen that in a while.

woops, that must have been because i was using my phone to do it. dont know how though, if i clicked it twice it should come up with an error message.

EDIT: hold on a minute, they are minutes apart, how'd that happen?

Behind You!
(as in there is somebody behind you who did it...spooky)

well, i took the equation which i got from xei and Specialis Sapientia, but i didnt quite understand how they got to it, i did in a way so i was able to come up with a way i understand better. and it was right, so thanks you two.

Originally Posted by slash112

well, i took the equation which i got from xei and Specialis Sapientia, but i didnt quite understand how they got to it, i did in a way so i was able to come up with a way i understand better. and it was right, so thanks you two.

So you've understood it now? Else I can try to draw a figure to help explain it better.

Originally Posted by khh

So you've understood it now? Else I can try to draw a figure to help explain it better.

yes i understand it now.

and just to be perfectly clear with that, i have always understood that acceleration is greater on a steeper slope (obviously), but it was how to get a=gsinx, but i understand now, well there is more than one way to get it.

Originally Posted by slash112

and just to be perfectly clear with that, i have always understood that acceleration is greater on a steeper slope (obviously), but it was how to get a=gsinx, but i understand now, well there is more than one way to get it.

Yeah, I figured that :p
It was how to think to find it, specifically, I meant. Good you got it, though :p

How did you get it? I don't think there's really any other way than resolving the force parallel to the slope.

well, when i say a different way i mean different substitution of f=ma etc.

Yes you resolve the force in the direction parallel to the slope and then use F=ma. That's the only way of doing it...

Originally Posted by Xei

Yes you resolve the force in the direction parallel to the slope and then use F=ma. That's the only way of doing it...

right, ill re-word what i said.

you substituted it in one way, i substituted it in another because i didnt fully understand yours at the time. but it doesnt matter anyway because it adds up to the same thing

Originally Posted by [SomeGuy]

Acceleration simply means a change in speed, whether faster or slower.

ACTUALLY, Acceleration is a change in speed as the object begins to move faster. Deceleration is the change in speed as the object slows down. Accerleration is not the change in speed WHETHER FASTER OR SLOWER.... Only faster.

Originally Posted by davej

ACTUALLY, Acceleration is a change in speed as the object begins to move faster. Deceleration is the change in speed as the object slows down. Accerleration is not the change in speed WHETHER FASTER OR SLOWER.... Only faster.

No, acceleration can be used either way, while deceleration is always a lowering of speed.

How do you figure that?