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Old 10-04-2012, 10:24 AM   #21
Ssargentslayer
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Quote:
Originally Posted by Kid_Thorazine
Velocity, assuming I'm understanding right, once the ball reaches it's apex and starts falling it will have negative velocity in terms of your grid, whereas acceleration will be a constant -g assuming you only track the ball once it's finished accelerating upwards, and Y would only be negative if the ball ended up at a lower point than where it started.

I'm also operating under the assumption that the velocity and acceleration hitting 0 doesn't count.

On the other hand it could be acceleration since depending on our frame of reference the acceleration becomes positive on the way down since it's adding to velocity instead of subtracting, actually that's probably what they are looking for. This is why my physics professor insisted on labeling opposing forces in degrees instead of dealing with positive and negative.

Your answer did not need to be this long.
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Old 10-04-2012, 10:25 AM   #22
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Originally Posted by JustRooster
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isn't acceleration a vector quantity aswell?
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Old 10-04-2012, 10:26 AM   #23
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Originally Posted by archenemyfan
isn't acceleration a vector quantity aswell?

Yup.
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Old 10-04-2012, 10:28 AM   #24
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Quote:
Originally Posted by archenemyfan
isn't acceleration a vector quantity aswell?


Yes, but in this model where a ball is thrown up, the acceleration is due to the force of gravity, which is assumed to be constant and always negative (as the ball is always attacted back to the ground)
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Old 10-04-2012, 10:40 AM   #25
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Velocity is speed in a certain direction. Seeings as the direction changes, i'd say that's your answer.
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Old 10-04-2012, 10:41 AM   #26
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Quote:
Originally Posted by Ssargentslayer
Your answer did not need to be this long.



It wasn't initially, half of it is me second guessing my first answer.
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Old 10-04-2012, 10:47 AM   #27
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ill give you an easy trick for you to use whenever you encounter such a problem:
whenever there's change in movement from the original direction to the opposed direction, velocity changes sign, and at the point where the change of directions happened, is whete the velocity is equal to zero.

other info, acceleration is always depending on an applied force, in your case gravity, and if there is no other forces applied during the movement, acceleration will stay constant, so in you case it will stay constant.
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Old 10-04-2012, 10:50 AM   #28
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Quote:
Originally Posted by Metallica1554
The answer is velocity because it is a vector quantity, hence speed and direction are taken into account. The direction that the ball is travelling in changes throughout the flight, so on the way back down the velocity becomes negative.

This. In much better words than I could put it in.

Although I'm still not convinced that gravity and accelleration are the exact same thing and not just correlated.

However, I'm a Communications major and haven't had to do this kind of shit in the greater half of a decade.
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Old 10-04-2012, 10:50 AM   #29
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Originally Posted by mulefish
But wouldn't it need a positive acceleration to start with? Seeming as the ball is thrown?

Velocity definitely changes though.


These problems always start a the time when the ball or whatever has left whatever is producing a force on it. So, what is happening is that something (persons arm) is producing a force on it. Once it has left the arm, it is now in free 'fall' motion. There is nothing to accelerate it upward anymore, only gravity to pull it down. The higher the velocity the longer it will keep moving in the upward direction. So, you would most likely have an acceleration that gives the object speed but think of it as a force that creates acceleration F = ma.

Quote:
Originally Posted by snipelfritz
Although I'm still not convinced that gravity and accelleration are the exact same thing and not just correlated.


Gravity is a Force that causes acceleration on objects within it's field. F due to gravity = (G)m1m2/d^2.

G is universal gravitation constant, m1 and m2 are masses of two objects, and those three terms divided by the distance between them squared gives the force of gravity. Which you can then apply to F = ma (I'm pretty sure... it's been awhile since I've done this).
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Old 10-04-2012, 11:08 AM   #30
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Yeah, it's velocity.
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Old 10-04-2012, 11:30 AM   #31
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Velocity. I think everyone's covered why it's not acceleration, but not why it's not position.

Your problem states that it starts at Y=0, goes up and comes back to it's starting point at 0 therefore it was always positive and didn't change sign.
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Old 10-04-2012, 11:37 AM   #32
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Gravity is just an acceleration. Gravitational force is caused by distortions in space/time.
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Old 10-04-2012, 11:41 AM   #33
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Originally Posted by magnus_maximus
Gravity is just an acceleration. Gravitational force is caused by distortions in space/time.

Magnus, what's your last name?
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Old 10-04-2012, 11:44 AM   #34
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Magnus, what's your last name?

Seximus Decimus Aurelius.

>_>
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Old 10-05-2012, 05:25 AM   #35
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Seximus Decimus Aurelius.

>_>

<_<

So it doesn't begin with a J?...

>_>
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Old 10-05-2012, 05:54 AM   #36
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Originally Posted by whoomit
<_<

So it doesn't begin with a J?...

>_>

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Old 10-05-2012, 06:11 AM   #37
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Do you have....

Ginger hair? >_>
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Old 10-05-2012, 06:12 AM   #38
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acceleration stays at -9.81m/(s^2). velocity is the property that changes, because the direction in which the object is travelling changes. SPEED doesn't change, velocity does. look into the difference if you don't know it already.
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Old 10-05-2012, 06:13 AM   #39
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Do you have....

Ginger hair? >_>

No.

GTFO. That's just insulting brah.
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Old 10-05-2012, 06:14 AM   #40
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No.

GTFO. That's just insulting brah.

Oh, okay. So your surname isn't Johnston(e)?
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