Puzzle Time (3)

[scoutt]

well since the last one was soooo easy what about this one?

Here is something for physicists.

Think of a wheel of a motor car in motion. There are two points on the wheel, one at the place where the wheel touches the ground, and the other right in the opposite direction from it, at the topmost location on the wheel. Can you tell if the speed of travelling of the wheel at both these points will be the same or different? (Referenced to the Ground)

[scoutt]

what, nobody has any guesses?

[fredricknish]

Different

?

[scoutt]

can you tell me why?

[grifter2]

The wheel doesn't touch the ground.

But, if it did, then both points would be moving at the same rate of speed.

Your question was kind of confusing though. Is there any way you can elaborate and be more specific?

[scoutt]

(Referenced to the Ground)

so think of it as a car wheel. so the bottom is touching the ground.

[grifter2]

If you're talking about two points on a wheel at a specific point in time, then both points would be going 0MPH in relation to the ground. Therefore, they would be going the same speed.

If, however, you mean to say that over a specified amount of time, would the rate of speed be the same for the two points on the wheel relative to the ground? Yes, they would be going the same speed.

[scoutt]

is that your final answer?

we'll wait for a few before I give my answer.

[fredricknish]

Originally posted by scoutt
can you tell me why?

I cannot find a good reason for my answer.But I have a strong feeling that its diffrent.

Are the two points on two diffrent wheels or are they in the same wheel?

[KWJams]

not sure if I understand the question correctly, but I would say if the wheel was turning the top would be faster than the bottom since the contact friction would slow down the bottom of wheel.
The weight of the car would cause the bottom of tire to flex outward which would disapate some of the energy and create a wider profile.

Trick part of puzzle is probably that nothing was said about a tire being on the wheel, and that would make my answer irrelevant.

[grifter2]

Originally posted by KWJams
not sure if I understand the question correctly, but I would say if the wheel was turning the top would be faster than the bottom since the contact friction would slow down the bottom of wheel.
The weight of the car would cause the bottom of tire to flex outward which would disapate some of the energy and create a wider profile.

Trick part of puzzle is probably that nothing was said about a tire being on the wheel, and that would make my answer irrelevant.

That would be true if he were talking about two points on the tire. However, even with tires on, the two points on the wheel would be going the same speed.

[KWJams]

Originally posted by scoutt
one at the place where the wheel touches the ground, and the other right in the opposite direction from it, at the topmost location on the wheel. Can you tell if the speed of travelling of the wheel at both these points will be the same or different? (Referenced to the Ground)


Hmmmmmmmmmm?
where the wheel touches the ground


I have this image of scoutt roflhao and all of us smacking ourselves in the forehead when he reveals the answer. :D

[grifter2]

Definitely:P

[fredricknish]

Could someone get that Green Monster in here?:D

[KWJams]

We will need to set bait out for him---like a plate of cookies.
:D

[scoutt]

somebody say cookies.....:D

KW was the closest.

ok here is the answer.

The wheel is on the ground, as of a running car. In this case the point at the top of the wheel travels at a speed more than the point at the bottom. This is what makes the wheel go forward instead of just spinning around. Also as the point at the top moves down, its speed decreases and hits the lowest when the point reaches the bottom.

[kevin]

If you're going to be very technical and say the bottom of the wheel (or tire) in contact with the ground is slightly flattend it will be travelling a little slower than the top of the tire wich is at its maximum distance from the center of the wheel, making it move a little faster relative to the ground than the bottom of the tire. If the wheel/tire is rigid, and the bottom is the same distance from the center of the wheel as the top, they both are moving at the same linear velocity relative to the ground (although in opposite directions), which could be anywhere from zero on up.

[kevin]

hmm...seems you posted an answer while I thought about it.

[transmothra]

if the points were fixed references, they would be travelling at the same speed, for obvious reasons. if, however, the points moved along the wheel as it rotated, then both would take turns going faster, depending on which one was above the hub/center.

<--
O
-->
rotation


<-- 'x' kph
velocity

[scoutt]

sorry Kev, but it sounds like you were close.

[kevin]

you seem to be mixing linear motion (relative to the ground) with circular motion. Both of which would be very different. The free rolling circular motion causing the car to move forward in the opposite direction of the circular motion of the tire at contact with the ground, that would mean the top of the tire is moving faster than the bottom relative to the ground, like you said, that is what makes the car actually move relative to the ground, but the linear motion of points A and B, relative to the ground, are the same, which is how I read your question.

[scoutt]

yeah but I was not sure how to re-word it at the time. I got the question from someone else and just posted it.

sorry if it was so vague...

[kevin]

no apology needed, its a very good question. Circular motion has many different aspects to it and is quite complicated. And since you threw in a little bit a of relative relationship (wheel to ground) its even more complicated. Its similar to your foot (and easier to visualize), the one in contact with the ground is going nowhere relative to the ground (zero velocity) but your body is being propelled forward. Then the other foot drops and the process begins over again. A wheel is like a foot that is always in contact with the ground, the part touching the ground is not moving relative to the ground, but it provides the friction required to propel the rest of the body in the opposite direction of the force.