GRED: Does a ball take longer to go up or come down?

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A ball is tossed in the air. Does it take longer to go up or come down?

Poll ended at Wed May 19, 2010 2:25 pm

Up.
157
17%
Down.
258
27%
Same.
524
56%
 
Total votes: 939

wh

Re: GRED: Does a ball take longer to go up or come down?

Post by wh » Wed May 19, 2010 2:08 am

To me, the force of air resistance is in both directions against the motion of the ball, and is in both directions proportional to the velocity at any point. Whatever the initial velocity, that is reduced by constant gravity, which is the same in both directions. However high the ball goes, it is from that height that it will have time to go down with the same acceleration as deceleration, with the same proportional drag against that motion. Ergo, aequum.

.

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RJN
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Re: GRED: Does a ball take longer to go up or come down?

Post by RJN » Wed May 19, 2010 2:41 pm

The poll is now closed and the correct answer is now included in the initial post at the top. - RJN

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neufer
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Re: GRED: Does a ball take longer to go up or come down?

Post by neufer » Wed May 19, 2010 2:58 pm

RJN wrote:The poll is now closed and the correct answer is now included in the initial post at the top. - RJN
Do these results differ significantly from the pre-open discussion poll results from last week?

I can understand people voting for "the same"
but I am rather baffled by the number of votes for "up". :-?

(All folks had to do was to wad up a piece of paper and toss it.)
Art Neuendorffer

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neufer
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Re: GRED: Does a ball take longer to go up or come down?

Post by neufer » Wed May 19, 2010 6:55 pm

Non self propelled objects that generally come down faster than they went up:
  • 1) Lawn Darts

    2) Paper airplanes

    3) Balsam/Styrofoam gliders set for a slow stall

    4) Kites
Art Neuendorffer

mndt

Re: GRED: Does a ball take longer to go up or come down?

Post by mndt » Thu May 20, 2010 4:28 pm

On the start of the way up the ball has a certain amount of energy.
k=(1/2)mv^2

But friction with air makes it lose some of it's energy. so K (on the way down) < K (On the way up)

Since m (mass) is the same. V (Velocity) should be less. so it takes more time for it to come down.

basic_user

Re: GRED: Does a ball take longer to go up or come down?

Post by basic_user » Thu May 20, 2010 5:55 pm

It depends. Consider a hand on a table with a ball sitting on the hand, and then the hand and ball moving up from the table. Assume the hand moves at a constant acceleration and the ball and hand are inelastic. Say the hand stops a foot above the table and the ball continues to rise. From this point above the table, ignoring air resistance, the ball takes as long to get to the top of its flight as to return to this spot, and its upward and downward velocities at this point are the same. The variable is what happens in the first foot. The falling ball crosses the distance at 1 g and comes to an immediate stop. The time for the upward rising ball to cross one foot depends on the acceleration of the hand. Generally, I would expect the hand to accelerate much faster than 1 g, so up would be faster than down. (If this weren't true we wouldn't be able to catch a ball that falls out of our hand.)

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neufer
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Re: GRED: Does a ball take longer to go up or come down?

Post by neufer » Thu May 20, 2010 8:07 pm

Hold a standard plastic soda straw crosswise on the middle of your four fingers with your thumb.

Then turn your palm over and toss the straw forward overhand as fast as you can
so as to give it a strong backspin as the straw rolls forward off your fingertips.

Does the straw take longer to go up or to come down?
Art Neuendorffer

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Re: GRED: Does a ball take longer to go up or come down?

Post by wonderboy » Fri May 21, 2010 3:30 pm

To me this is simple.

Of course the ball is going to go faster upwards than it is downwards. This is because when you throw the ball upwards you are using a force greater than that of gravity (initially) to make the ball rise. on the way down, there is no initial force. Both ways the ball will encounter drag which will slow it down, so therefore a ball rising with a force greater than that gravity will rise quicker than a ball which falls relying solely on gravity.



Paul
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Guest

Re: GRED: Does a ball take longer to go up or come down?

Post by Guest » Sun Jul 22, 2018 7:34 pm

If a ball is bounced hard enough, can it travel faster upward than it does if dropped downward from the same height? In other words, if I dribble a ball, after I bounce it will it come to my hand faster than it dropped from my hand( let’s just say it’s the same distance )

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Re: GRED: Does a ball take longer to go up or come down?

Post by BDanielMayfield » Tue Jul 24, 2018 2:58 am

I didn't notice this quiz until after the voting had closed, but in all honesty I too would have gone with the overwhelming majority who selected "same". But, on the bright side, this result reaffirms my skeptism about just accepting "consensus" opinions. :wink:

Bruce
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