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T APLUS 22
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October 2003

Re: Physicist please read.

Thu, 07 April 2005 15:02

hickoz_bro wrote on Thu, 07 April 2005 16:38

WTF?!?! this is stupid....

the ball has a mass which is not important since we're not considering air resistance... and a velocity at any point in time... barrys hand also has a velocity at any point in time, but it's only important up to the point where the ball leaves barrys hand...

gravity is constant 9.8m/s/s (meters per second, per second) on earth, air resistance is nill...

newtons 3rd law is only true for systems in equilibrium, IE, stationary, or constant speed. as soon as forces are unbalanced ie, barry hurls the ball up, then obviously there's accelletarion for a time, say barry accelerates the ball to a speed of 20m/s immediatly after the ball leaves barrys hand it starts to slow down at the rate which gravity acts on it, 9.8m/s/s there for it will reach it's maximum height of 20.29m at t=2.04sec (where t=0 is where the ball left barrys hand)

the moral of the story is:
Kim is right, but she's talking about when barry throws the ball,
Barry is right, but he's talking about the ball stationary in his hand.
kathy is both right and wrong, she's wrong 'cause she says the others are wrong, but she's right 'cause in this case the reactive force to barrys hand is the weight of the ball multiplied by the force due to gravity. hence, as kim stated if barry overcomes this force, then he'll accelerate the ball.

basically your all right, but your talking about the senario at different stages, or saying it in a different way...

anyone care to argue that, can go and unbalance their forces over a cliff

not to sure about this. I think you've got a good idea, but get lost using the wrong terms.
for starters, Kim is never right at any time. A quick look at the 3rd law will show this.

Corona RT142 statement is correct.
St184 makes a notable point about the reaction of the earth moving away from the ball.
And River (who I was secretly hoping would join this discussion) is also correct.
However I think barry just confused: "the ball should remain stationary or at constant velocity if the forces are equal" this is true if the SUM of all forces acting on an object are equal. The force barry initially mentions is the 'Action (hand on ball) - Reaction (ball on hand) force. This action-reaction pair of forces aren't the only forces in the 'isolated' system.

Its kim's statement that doesn't quite make sense.
"the reaction force to Barry's hand is gravity", I'm not convinced. The reaction to barry's hand moving up is the earth moving away from his hand. However if talking about the action of barry's hand applying a force to the ball and moving it up, then the REaction is the ball applying a force that moves barry down (effectively this is so minute it's considered not to exist). But by using [b] "so" [b] in "so as long as Barry exerts more force than gravity does he can throw the ball" it would appear that she uses part one of her sentence (which is correct) to back up part two. Even though part two is correct (I'm pretty sure) part one doesn't prove.

All barry has to do is apply a force with a greater magnitude than Gravity to throw the ball up.
hence, Kim is also right (dependent on the interpretation of the queston)

I invite people to submit there suggestions. I won't of course give everyone the same attitude as I gave hickoz_bro...but if you submit with the same arrogance as hickoz-bro...what do you expect.

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