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-   -   Science Something amazing to tell you concerning physics and motion (https://chiefsplanet.com/BB/showthread.php?t=208580)

cdcox 06-04-2009 07:15 PM
Quote:
Originally Posted by orange (Post 5818214)
Who said there's no friction? It won't roll if there's no friction - the skateboard will just slide effortlessly.

I've pointed out several times that more is better as far as friction between the wheels and treadmill.



[edit]

... or what HE said. :LOL:
In classical physics, it is very common to describe something rolling frictionlessly, without sliding. What this means is that there is no energy lost due to friction in the rolling process. It does not mean that there is so little friction that there is a difference between the velocity of the road (or treadmill) and the road. In classical physics, you could say a car operating under normal conditions is rolling frictionlessly. Under braking conditions, friction is significant.

You would need friction to be equal to the jet thrust to keep the plane from moving relative to the ground.

Mizzou_8541 06-04-2009 07:15 PM
Quote:
Originally Posted by orange (Post 5818223)
Come to North Denver. There are plenty of little Mexican restaurants where you can do that. Don't expect to get the right change, though.

Hmmm. Maybe that's already where the problem is set.
:D

MagicHef 06-04-2009 07:17 PM
Quote:
Originally Posted by Baby Lee (Post 5818226)
Clarifying, not friction between the wheel and the ground, friction reeruning the rotation of the wheel.

You do get that there can be 'rolling without slippage' and still negligible reerunation of rotation, given negligent wheel mass and negligent bearing friction.

Think about the analogy and explain to me how you can pull yourself along the rope forward, no matter how fast the treadmill is going the opposite direction.
Stop it.

Psyko Tek 06-04-2009 07:17 PM
Quote:
Originally Posted by Jenson71 (Post 5816281)
This blows my mind.

Okay, say you have two ball bearings. You hold one in your hand and drop it. The other you put in a gun, point it straight forward, as level as the one in your hand, and pull the trigger, sending it hundreds of yards.

Which one lands first?

The one dropped in your hand right? RIGHT!?!?

No, actually they both hit the ground at the same time.

This is because the vertical component of motion is the same for both objects. They both fall vertically the same distance at about 10 meters per second squared (gravity, actually more like 9.8).

But Jenson, Jenson! What about the horizontal component of the gun-fired ball bearing? Actually, when air resistance is small enough to ignore as it is in this case (being that the bearings are exactly alike), the horizontal and vertical components of a projectile's velocity are completely independent of one another.

And, in this experiment, the gun-fired bearing is constantly falling from the moment it is fired. Yes, it looks like it is holding up in a straight line, but, it's actually falling and it's just hard to see with our eyes. And again, it is falling at exactly the same speed as the ball bearing you released in your hand -- the speed of gravity.

Post more cool science things in this thread.

I think I will later post Aristotle vs. Galileo and gravity, for a little history spin on science.
first joint?

orange 06-04-2009 07:18 PM
Quote:
Originally Posted by Baby Lee (Post 5818226)
Clarifying, not friction between the wheel and the ground, friction reeruning the rotation of the wheel.

You do get that there can be 'rolling without slippage' and still negligible reerunation of rotation, given negligent wheel mass and negligent bearing friction.

Think about the analogy and explain to me how you can pull yourself along the rope forward, no matter how fast the treadmill is going the opposite direction.
One - I think your analogy fails on a different point - anchoring the rope to the wall. To exert force using the rope, you have continually move your grip up the rope. Instead, put a huge wind machine fan behind you.

Two - In this instance, you will stand on the skateboard, the wheels will roll, the treadmill will roll under the wheels and you will remain in one spot.

[edit] Tried goodling "skateboard treadmill" to find a demonstration. I only see videos of failed attempts, so far, but I did find this on page one http://answers.google.com/answers/threadview?id=428718

This is a popular problem.

Baby Lee 06-04-2009 07:24 PM
Quote:
Originally Posted by MagicHef (Post 5818233)
Stop it.
Jesus Christ you are locked in. You stop.

Reality wins.

I get that your reading of the hypothetical demands Hurculean rolling resistance, otherwise the conveyor fails in it's job.

But since IN EVERY EMPIRICAL INSTANCE, bearing friction is in fact negligible wrt to 4 jumbo jet at full thrust, the conveyor WILL fail in it's job and the plane will take off.

Have you figured out how to stop me from inching forward as I pull the rope while I ride the skateboard on the treadmill, lemme guess superfriction always equalling and negating my muscle capacity.

I understand the conundrum, as well as you. This is getting tedious.

Baby Lee 06-04-2009 07:29 PM
Quote:
Originally Posted by orange (Post 5818236)
One - I think your analogy fails on a different point - anchoring the rope to the wall. To exert force using the rope, you have continually move your grip up the rope. Instead, put a huge wind machine fan behind you.

Two - In this instance, you will stand on the skateboard, the wheels will roll, the treadmill will roll under the wheels and you will remain in one spot.

[edit] Tried goodling "skateboard treadmill" to find a demonstration. I only see videos of failed attempts, so far, but I did find this on page one http://answers.google.com/answers/threadview?id=428718

This is a popular problem.
Yeah, there's only 300 pages on Mythbusters website. 300 pages, not posts, pages.

That's why this has gotten tedious. People keep reiterating the same hash of misconceptions and consequences of the ambiguity of the hypothetical.

headsnap 06-04-2009 07:37 PM
I can't believe that over 200 posts have been dedicated to this stoopid question...

Quote:
Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?
The bolded part is physically impossible realistically or theoretically, that is unless the treadmill is also powered by jet engines that accelerate the entire treadmill and conveyor belt at the opposite direction at the same rate the Jet accelerates, because unless the jet is anchored, it's gonna accelerate!


including the OP, there is a whole lotta' dumb in this thread...

cdcox 06-04-2009 07:41 PM
Imagine a person sitting in a chair, as wide and as long as the persons' ass. The person sitting in the chair pulls up on the seat of the chair with a force designed to exactly match the force needed to elevate the chair. Can the chair take off?

orange 06-04-2009 07:43 PM
Quote:
Originally Posted by Baby Lee (Post 5818256)
Yeah, there's only 300 pages on Mythbusters website. 300 pages, not posts, pages.
Quote:
Originally Posted by headsnap (Post 5818272)
I can't believe that over 200 posts have been dedicated to this stoopid question...
[/i]
This thread has already had an impact elsewhere on ChiefsPlanet: http://www.chiefsplanet.com/BB/showt...207709&page=17

orange 06-04-2009 07:46 PM
Quote:
Originally Posted by headsnap (Post 5818272)


The bolded part is physically impossible realistically or theoretically, that is unless the treadmill is also powered by jet engines that accelerate the entire treadmill and conveyor belt at the opposite direction at the same rate the Jet accelerates, because unless the jet is anchored, it's gonna accelerate!
In MY version - the treadmill is free-spinning. It does match the speed of the wheels perfectly, and it is also powered by jet engines - the same jet engines that are powering the plane.

orange 06-04-2009 07:47 PM
Quote:
Originally Posted by cdcox (Post 5818282)
Imagine a person sitting in a chair, as wide and as long as the persons' ass. The person sitting in the chair pulls up on the seat of the chair with a force designed to exactly match the force needed to elevate the chair. Can the chair take off?
I could do that easily (145 lbs.). I've known many people who would (and have) turned that chair into kindling.

headsnap 06-04-2009 07:48 PM
Quote:
Originally Posted by orange (Post 5818293)
powered by jet engines - the same jet engines that are powering the plane.
how?

cdcox 06-04-2009 07:50 PM
Quote:
Originally Posted by orange (Post 5818297)
I could do that easily (145 lbs.). I've know many people who would (and have) turned that chair into kindling.
What if the chair were infinitely strong (and frictionless)?

orange 06-04-2009 07:52 PM
Quote:
Originally Posted by headsnap (Post 5818299)
how?
As the wheels exert force against the treadmill due to the engine's thrust, the treadmill exerts an equal and opposite force against the wheels. This causes the wheels to roll. It also causes the free-spinning treadmill to roll in the opposite direction.

Use the advanced search for my posts in this thread. You might miss some of the comments to me by others, but I don't think so; I think I've quoted them all in my responses.


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