[Guest]

LIS's little cannonball problem reminded me of this one.

You throw a ball up in the air.

It goes up. It comes down.

You catch it at the same height you threw it from.

Now, did it take longer going up, or coming down?

Don't forget air resistance

[Guest]

Just because something is mentioned in the OP doesn't mean it's important.

I don't know about you, but when someone says "don't forget" something, I take that something to be important to the issue.

[Guest]

I don't know about you, but when someone says "don't forget" something, I take that something to be important to the issue.

Quite right, flowstoneknight, you've defended your case well. And for those saying it's too small to be significant, I didn't suggest it would take much longer going in either direction. It could take a tiny fraction of a second longer coming down, but longer is longer.

Incidentally, I think the principle may be easier to visualise if you imagine doing it with a shuttlecock instead. Admittedly shuttlecocks change shape when they go faster so the drag is less consistent, but it still works in the same direction. Any object where drag is significant, such as a cotton-wool ball, will provide a similar demonstration.

[Guest]

I agree. Although if you wanted to bring air resitance into it then you could say that air fesistance on the way up would have to be the same as air resistance on the way down (assuming the object is a standard symetrical shape, a sphere is best I think). This would increase the acceleration on the way up, and decrease the acceleration on the way down by the same amount. Effictively cancelling each other out. But air resistance (as stated before) is so neglible it would only make any noticeable difference if we could throw incredubly high, but that won't be happening.

The only thing I can think of that would cause going up to be slower than coming down would be the shape of the thrown object. If a yramid was thrown point upwards it would go up faster than it would come down.

First post says it it's a ball - that's a sphere, lets leave out complicated shapes!

Nice try, but you're forgetting that on the way up, you threw the ball. The only force acting on the ball on the way down is gravity, accelerating from zero. My answer is correct (edit: as long as it is a symmetrical object). We can talk about impulses and everything, and drag, and acceleration, but you will find that the speed at which the ball leaves your hand will be the same speed it hits your hand at.

interestingly simple! so if you can throw it more than 9.81m/s/s it will return faster than gravity - just need to see how fast we can throw it!

Also if we throw it at less than 9.81m/s/s then it's not going to fall as fast as terminal velocity! maybe true as it takes some time to free fall at max speed.... lets see!

Because air resistance doesn't work on balls that are thrown?

Pretty sure it works wherever there is air - and in any direction!

just my thoughts - out here in space it can be lonely! I was thrown here by octopuppy - hope he will catch me when I come down!

[Guest]

Think about a balloon, a perfectly round one, or any ball with a high wind resistance/low weight (beach ball?). I'm thinking it will never fall as fast as you can throw/hit it upwards. So long as you can make it go faster than terminal velocity for that object, it will come down slower. then again, IANAP.