Something amazing to tell you concerning physics and motion

[Jenson71]

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.

[cdcox]

Originally Posted by MagicHef

This is not the same scenario. The wheels and the side walk are not moving at the same speed.

You are setting up an impossible tautology.

Say that the side walk senses how fast the wheels are moving and then matches that speed. Let's say at instant 1 the sidewalk has zero velocity and the tow rope has a velocity of +5.

instant = 0; tow rope velocity = 5; wheel velocity = 5; sidewalk = 0

instant = 1; tow rope velocity = 5; side walk velocity = 5; what is the wheel velocity? 10!

So instant =2 tow rope velocity =5 sidewalk velocity =10; wheel velocity = 15 etc.

The wheels will always be spinning faster than the side walk because the speed of the tow rope is externally setting the speed of the person.

[orange]

Originally Posted by Silock

My car doesn't have rockets strapped to the roof. If it did, a treadmill wouldn't do a damn thing to keep it in place, even if the speedometer were reading "0".

Originally Posted by KC Fish

The conveyor belt is totally irrelevant compared to the dynamics of flight.

The plane's jets push air in the opposite direction. The air that is pushed in the opposite direction of the plane is not affected by the ground. The only thing the tires do is hold the plane off the ground until a sufficient amount of air is pushed behind the plan to gain lift from the airflow over the shape of the wings.

A care pushes the ground in the opposite direction. Completely totally different.

It simply does not matter. If you're moving forward while in contact with the ground, your wheels are turning. ALL of your forward motion on the ground goes through the wheels. And ALL of it will be negated by a treadmill which can spin freely.

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Troy Allen • Jan 30 2008 • 10:53PM
I am completely disappointed at Mythbusters handling of this experiment. The science they used and the “explanations” were both completely flawed. The original myth, and ALL of the discussion, centered around one central conceit: The plane would have NO FORWARD MOTION RELATIVE TO THE GROUND because of the conveyor belt matching the speed of the plane. NOT the “speed of the WHEELS of the plane” or any other contrived version.

Of course the plane is going to take off if it has enough forward motion RELATIVE TO THE GROUND to create the Bernoulli effect required to lift the wing because of the airflow over the wing.

I really expected more “science” from MythBusters. They almost explained it properly with the “model car example”. I guess it was the original Myth that was flawed, or my understanding of the Myth. I guess in their mind the myth is that no plane on a conveyor belt can take off if the “speeds are matching in opposite directions”. That is far too simplistic to make a determination, so it is flawed from the get-go.

Those of us who claimed the plane would not take off without forward motion relative to the ground due to the laws of physics are still correct. The planes both had significant forward motion relative to the ground. I just hope everyone involved in the debate understands these distinctions, otherwise this will just dumb down the TV watching public a bit more. It sure was fun though!

[MagicHef]

Okay, if the wheels of the plane are buried in concrete strongly enough to prevent the plane from moving, will it take off?

[cdcox]

The jet engines would also move air over the wings even if the plane were somehow stationary relative to the ground. Jet engines are like air pumps. Someone standing in front of a jet on this magic tread mill would experience wind from the jet engines, even on a calm day.

[Silock]

Originally Posted by MagicHef

Okay, if the wheels of the plane are buried in concrete strongly enough to prevent the plane from moving, will it take off?

Depends on how strong the engines are.

[MagicHef]

Originally Posted by cdcox

You are setting up an impossible tautology.

Say that the side walk senses how fast the wheels are moving and then matches that speed. Let's say at instant 1 the sidewalk has zero velocity and the tow rope has a velocity of +5.

instant = 0; tow rope velocity = 5; wheel velocity = 5; sidewalk = 0

instant = 1; tow rope velocity = 5; side walk velocity = 5; what is the wheel velocity? 10!

So instant =2 tow rope velocity =5 sidewalk velocity =10; wheel velocity = 15 etc.

The wheels will always be spinning faster than the side walk because the speed of the tow rope is externally setting the speed of the person.

Yes, the tow rope is externally setting the speed of the person. There is nothing externally setting the speed of the plane.

[Buck]

Originally Posted by orange

It simply does not matter. If you're moving forward while in contact with the ground, your wheels are turning. ALL of your forward motion on the ground goes through the wheels. And ALL of it will be negated by a treadmill which can spin freely.

The only thing that is affected is the wheels, and so they spin, instead of just sitting still. The rest of the plane moves forward without being affected whatsoever from the treadmill.

If the plane is going 200 mph forward and the treadmill is going 50 mph backwards, then the wheels will be spinning at 50 mph. If the plane is going 1,000,000 mph forward and the treadmill going 3.2 mph backwards, then the wheels will be spinning 3.2 mph backwards.

The rest of the plane is moving forward without being affected.

[MagicHef]

Originally Posted by cdcox

The jet engines would also move air over the wings even if the plane were somehow stationary relative to the ground. Jet engines are like air pumps. Someone standing in front of a jet on this magic tread mill would experience wind from the jet engines, even on a calm day.

The engines are mounted under wings specifically to prevent the turbulence caused by them from affecting the wings. The airflow over the wings from no movement with the engines on would be minimal.

[MagicHef]

Originally Posted by MediaCenterJunkie

The only thing that is affected is the wheels, and so they spin, instead of just sitting still. The rest of the plane moves forward without being affected whatsoever from the treadmill.

If the plane is going 200 mph forward and the treadmill is going 50 mph backwards, then the wheels will be spinning at 50 mph. If the plane is going 1,000,000 mph forward and the treadmill going 3.2 mph backwards, then the wheels will be spinning 3.2 mph backwards.

The rest of the plane is moving forward without being affected.

Um, no. The wheels are attached to the plane.

[Buck]

Originally Posted by MagicHef

Okay, if the wheels of the plane are buried in concrete strongly enough to prevent the plane from moving, will it take off?

No, but then you cant have a conveyor belt going under it either.

[MagicHef]

Originally Posted by MediaCenterJunkie

No, but then you cant have a conveyor belt going under it either.

The effect (no horizontal velocity) is the same.

0 + X + (-X) + 0 = 0

[Fish]

Originally Posted by orange

It simply does not matter. If you're moving forward while in contact with the ground, your wheels are turning. ALL of your forward motion on the ground goes through the wheels. And ALL of it will be negated by a treadmill which can spin freely.

How does a plane move forward through the air, once it is off the ground? What gives it forward motion if the wheels are not passing all forward motion on the ground? How do you explain forward motion without the ground contact you are defending?

By your definition, the plane should not be able to progress once the forward motion on the ground is no longer going through the wheels....

[Buck]

Originally Posted by MagicHef

Um, no. The wheels are attached to the plane.

The wheels would be moving forward at Okay, I guess then they would be spinning at 999,996.8 mph

Sorry.

[MagicHef]

Originally Posted by MediaCenterJunkie

The wheels would be moving forward at Okay, I guess then they would be spinning at 999,996.8 mph

Sorry.

At that point, they would not be moving at the same speed as the treadmill, which is a requirement of this scenario.

[orange]

Originally Posted by cdcox

The jet engines would also move air over the wings even if the plane were somehow stationary relative to the ground. Jet engines are like air pumps. Someone standing in front of a jet on this magic tread mill would experience wind from the jet engines, even on a calm day.

Jet engines are UNDER the wings. They have absolutely no chance of producing enough lift to take off.

You know, $BILLIONS are spent on airports with runways. Think of all the savings if actual engineers were as smart as Mythbusters. We could just put the planes' wheels on a couple treadmills like at the emissions testers - presto, instant VTO.