[rookie1ja]

The Ball - Back to the Logic Puzzles
How can you throw a ball as hard as you can and have it come back to you, even if it doesn't bounce off anything? There is nothing attached to it, and no one else catches or throws it back to you.


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Spoiler for Solution

Ball - solution
Throw the ball straight up in the air.

Spoiler for old wording

How can you throw a ball as hard as you can and have it come back to you, even if it doesn't hit anything, there is nothing attached to it, and no one else catches or throws it?

[Paul]

This is not as elegant a solution, but...

If you were on a planet with just the right mass and diameter, you're hardest throw in the right direction would allow the ball to orbit the planet once (or twice, etc. depending on the constants just mentioned).

[uhungus]

Could you not throw the ball up a slope/hill? Does that count as the ball hitting something (the ground)?

[rookie1ja]

"uhungus":d66ff said:

Could you not throw the ball up a slope/hill? Does that count as the ball hitting something (the ground)?

That would not fit the initial condition of not hitting anything.

[clarinetman]

I am assuming that we are throwing this ball on the planet Earth...so in the answer the ball can be touching air and using the force known as gravity.

One solution is to throw the ball directly into a stream of circular air (possibly a tornado/hurricane....but those are a bit dangerous) and catch it on the way back.

[Grujah]

My solution was that, while throwing the ball, you rotate it towards you, so once it hits the ground it will get back.. does that count as valid?

[planeterry]

What if I threw it up at an angle, and then ran as quickly as I could and simply caught it as it came back down at the far end of the arc? Nobody said that I had to stand in one place.

[fosley]

Well, technically speaking, to throw the ball straight up and to let it orbit the planet once first are one and the same. In both cases, you accelerate the ball away from gravity without achieving escape velocity, then gravity pulls it back around in an orbit. Standing on Earth and throwing it straight up, you have a very eccentric orbit that crosses paths with the planet's surface--meaning it'll come out of orbit very rapidly before it actually makes a complete revolution--but you are essentially doing the same thing either way.

Also, technically speaking the ball hits billions of air molecules on the way up, but the scenario would work the same without air. If you want to allow contact with air, you could spin it really, really fast, and make it come back to you like a boomerang, or do like Clarinetman suggested and throw it into a stream of moving air. I've actually shot arrows at an angle away from me so they came back to me with the wind, but I was still relying a lot on gravity.

Or you could have a transforming ball that converts to a flying machine after you throw it, like those little bombs the Green Goblin uses in Spiderman!

[Skumbag]

Well, I was going to say throw it really hard and fast in a straight line, so hard that it goes right round the planet. It'd be a bit hard, though.

Another possible one takes the assumption that the ball was made of metal (like a shot-putt) and you had an industrial strength magnet (the type you need a license for), but if that was the case it'd be impossible to do, as the magnet would go with the ball.....

[fosley]

What about a junkyard-strength electromagnet? They can lift entire cars with them, so surely it could pull the ball back, then you just flip the switch to off and you've got the ball back. To avoid contacting anything, you could just time the electromagnet so it turns off before the ball hits it, and you catch it in mid-air. Of course, you'd want to make sure you aren't wearing anything metallic when you turn the electromagnet on.