Something amazing to tell you concerning physics and motion

[Frosty]

Then where does the force of the engines go? If they are thrusting at so many pounds against the air, there has to be an equal force against the plane to keep it from not moving. That means you are saying that the treadmill is exerting the same force against the plane as the engines, but since the wheels are spinning, how can that be? They would have to have tremendous friction to match the engines' force.

[MagicHef]

Originally Posted by arc

Then where does the force of the engines go? If they are thrusting at so many pounds against the air, there has to be an equal force against the plane to keep it from not moving. That means you are saying that the treadmill is exerting the same force against the plane as the engines, but since the wheels are spinning, how can that be? They would have to have tremendous friction to match the engines' force.

Yep.

[Frosty]

Originally Posted by MagicHef

Yep.

So what kind of magic material do you have that would create that much friction against standard rubber tires?

[MagicHef]

Originally Posted by arc

So what kind of magic material do you have that would create that much friction against standard rubber tires?

This is not a question of material properties, which is certainly getting into details that I don't think are necessary for an inherently impossible situation. Assume that there is a material "MagicHefium" that makes the amount of friction necessary possible.

[Frosty]

Originally Posted by MagicHef

This is not a question of material properties, which is certainly getting into details that I don't think are necessary for an inherently impossible situation. Assume that there is a material "MagicHefium" that makes the amount of friction necessary possible.

It most certainly makes a difference. For friction forces to match the thrust of the jet engines, the tires would last a millisecond before melting down, at which time the jet would begin moving down the runway, scrapping along on its struts.

[orange]

Originally Posted by arc

It most certainly makes a difference. For friction forces to match the thrust of the jet engines, the tires would last a millisecond before melting down, at which time the jet would begin moving down the runway, scrapping along on its struts.

Again, friction forces don't really enter into it. You WANT high friction, but whatever friction you have is going to apply equally to the wheels and the treadmill.

The operative variable is resistance to the treadmill spinning freely.

[MagicHef]

Originally Posted by arc

It most certainly makes a difference. For friction forces to match the thrust of the jet engines, the tires would last a millisecond before melting down, at which time the jet would begin moving down the runway, scrapping along on its struts.

You realize the friction in question is in the wheel bearings, not the tires, right? Besides, those are made of MagicHefium, so no worries there.

[orange]

Originally Posted by arc

Then where does the force of the engines go? If they are thrusting at so many pounds against the air, there has to be an equal force against the plane to keep it from not moving. That means you are saying that the treadmill is exerting the same force against the plane as the engines, but since the wheels are spinning, how can that be? They would have to have tremendous friction to match the engines' force.

As I mentioned earlier, perfect rolling requires infinite friction.

We don't need to go that far, though. See my last post.

[cdcox]

Originally Posted by orange

As I mentioned earlier, perfect rolling requires infinite friction.

We don't need to go that far, though. See my last post.

Actually, perfect rolling generates zero frictional force opposing the thrust of the jets.

[orange]

Originally Posted by cdcox

Actually, perfect rolling generates zero frictional force opposing the thrust of the jets.

The friction I am talking about is the friction between the wheels and the ground/treadmill. This is the coefficient of friction.

For dragging you want low. For rolling you want high.