Physics puzzle

Well, didn't mean to heat things up.

I just think it's a little condescending to post an elementary school puzzle on a forum with mostly intelligent people, particularly to do so with nothing but an elementary school answer in mind. Same as how if you ask what is 2+2 on 2+2 forums, you probably aren't doing it to hear "4".

My explanation is simple. When the car accelerates everything in it not affixed will be pushed towards the back of the car, because a body at rest wants to stay at rest. However, there is only so much space in the back of the car. Air is heavier than helium, so it will push the balloon out of the way, towards the front.

As the father of three, we have balloons in the car once in a while and I've observed this. Of course I bore my kids with an explanation of why every time.

Quote: P90

Well, didn't mean to heat things up.

I just think it's a little condescending to post an elementary school puzzle on a forum with mostly intelligent people, particularly to do so with nothing but an elementary school answer in mind. Same as how if you ask what is 2+2 on 2+2 forums, you probably aren't doing it to hear "4".

It's overly simplistic to call this an elementary school problem. We must make assumptions and answer questions based on those assumptions. If, however, this forum was composed of physicists, then we would have to clarify every aspect of the problem. For instance, I assumed that the acceleration was positive and that the acceleration was linear and not rotational. It was quite easy to determine the intent of the question, and for most of us, the answer is counter intuitive, which makes it a good problem to reason through.

I think we got some serious mileage out of the airplane/treadmill question, didn't we? That one always seems to confound some pretty smart people.

I remember in physics class, after watching 2001 A Space Odyssey, discussing the weight felt by the guy running around the space craft ring. Depending on the direction and speed he might weigh a lot or very little. Then there were the Liliputions and Brobdignags from Gulliver's Travels and bone strength and eating to produce body heat. Things get complicated when you leave the perfectly spherical vaccum and enter the real world.

Quote: P90

I just think it's a little condescending to post an elementary school puzzle on a forum with mostly intelligeparticularly to do so with nothing but an elementary school answer in mind. Same as how if you ask what is 2+2 on 2+2 forums, you probably aren't doing it to hear "4".

I don't know what part of it you found ccondescending, it was not my intent. I like this puzzle, because it is an elegant, and somewhat non trivial illustration of the equivalence priciple. Most people I have discussed it with so far (including on this forum) sem to have found it at least amusing.
I am sorry if it turned out to be too simple for your level of fundamental understanding of elementary physics, I guess, I have some growing to do before I can match it.
Not sorry for posting the puzzle though - still think, it was a good riddle for those of us, not quite advanced in these matters as you are.

All I know is if Monty knows where the car is, then you should switch doors.

Quote: downtowner

I remember in physics class, after watching 2001 A Space Odyssey, discussing the weight felt by the guy running around the space craft ring. Depending on the direction and speed he might weigh a lot or very little.

I hate to change the topic, but what is the answer? I assume the ring rotated at a speed to exactly simulate earth gravity. My guess is that the runner would feel the same way running in either direction, for the same reason in an airplane it requires the same effort to walk toward the front of the cabin as away from it. Then again, physics is not my area of expertise.

Quote: CrystalMath

If, however, this forum was composed of physicists, then we would have to clarify every aspect of the problem.

Well, it has its good share of mathematicians, which is close enough.

Quote: weaselman

Not sorry for posting the puzzle though

Never said you should be. I'm just saying - when people post school questions in a non-school forum, they usually expect a more thorough look at them than in the classroom, like figuring out situations where the answer can be different. So it's surprising to me that you only expect unequivocal "box A" and reject any look at variations in conditions as irrelevant.

For one, particularly surprising that you would.

Put it this way: Suppose you were using this setup in a system where the outcome matters. Let's say the balloon is to serve as a hydrogen leak detector, with string deflection triggering emergency tank evacuation. Why do it this way is not up to you. Would you still be satisfied with the same "box A" answer?

Quote: Wizard

I hate to change the topic, but what is the answer? I assume the ring rotated at a speed to exactly simulate earth gravity. My guess is that the runner would feel the same way running in either direction, for the same reason in an airplane it requires the same effort to walk toward the front of the cabin as away from it. Then again, physics is not my area of expertise.

It's not my area, either, but all SF readers learn this :)

The answer is he would feel "heavier" if he ran in the direction of rotation, and "lighter" if he ran in the opposite direction. That's because int eh first case he'd be adding to the speed, just as if the ring ran faster. Contrariwise, he diminishes speed if he runs opposite to the rotation, and the effect would be the same as if the ring ran slower.

How much he feels either effect depends on how fast he can run.