Science Something amazing to tell you concerning physics and motion - Page 17

Jenson71 · 06-04-2009, 10:15 AM

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.

MagicHef · 06-04-2009, 03:36 PM

Quote:

Originally Posted by cdcox

Simply stated, it cannot.

find x:

x = x +5

Yep. That was Sully's point.

orange · 06-04-2009, 03:37 PM

Quote:

Originally Posted by cdcox

Simply stated, it cannot.

find x:

x = x +5

Why? What relevance has that got?

Frosty · 06-04-2009, 03:37 PM

Quote:

Originally Posted by MagicHef

No. The plane's engines provide horizontal force.

Which would move the plane horizontally, just like my balloon. The wheels only hold the plane up off the ground.

It's also like maglev trains, which need no contact with the ground to move forward with an external force (in this case a magnetic force).

Fish · 06-04-2009, 03:37 PM

bdeg · 06-04-2009, 03:38 PM

Quote:

Originally Posted by orange

The force is counteracted by the treadmill spinning in the opposite direction.

It's really simple. In order to go forward, the wheels have to roll or slide along the ground. What else, teleport?

Our ideal treadmill allows no sliding. And it matches the wheels' rolling in the opposite direction.

that is not possible.

go to a sporting good store or your garage

find a roller skate or blade

put a hand in it, and with your other hand move the wheels

is your hand in the skate pulled by the wheels?

or are you just making the wheels spin?

and.. your free hand is the conveyor

**Buck** · 06-04-2009, 03:39 PM

Here is my postulate.

A 747 cannot take off without moving forward relative to the ground, however the speed at which its wheels spin on a treadmill do not have any affect on the 747 moving forward.

MagicHef · 06-04-2009, 03:39 PM

Quote:

Originally Posted by arc

Which would move the plane horizontally, just like my balloon. The wheels only hold the plane up off the ground.

It's also like maglev trains, which need no contact with the ground to move forward with an external force (in this case a magnetic force).

Due to the structure of the question, it is impossible for the plane to move horizontally.

orange · 06-04-2009, 03:40 PM

Quote:

Originally Posted by MagicHef

Yep. That was Sully's point.

Quote:

Originally Posted by orange

Why? What relevance has that got?

I answered Sully.

I guess some of you are missing something. Force vs. resistance produces equal and opposite reactions. The exact same force that causes the wheel to turn also causes the treadmill to turn at the exact same time. There's no "this then that."

MagicHef · 06-04-2009, 03:41 PM

Quote:

Originally Posted by MediaCenterJunkie

Here is my postulate.

A 747 cannot take off without moving forward relative to the ground, however the speed at which its wheels spin on a treadmill do not have any affect on the 747 moving forward.

Independently, I agree. But the sum of the wheel speed and the treadmill speed determine the plane's speed.

Frosty · 06-04-2009, 03:41 PM

Quote:

Originally Posted by MagicHef

Due to the structure of the question, it is impossible for the plane to move horizontally.

Only because the force can't be transferred to the ground because of the spinning treadmill?

**cdcox** · 06-04-2009, 03:42 PM

Quote:

Originally Posted by MagicHef

No matter what speed the wheel is spinning at?

Well you could design bearings that had more friction, but that would then be the bearings that was keeping the plane from taking off instead of the treadmill.

MagicHef · 06-04-2009, 03:43 PM

Quote:

Originally Posted by arc

Only because the force can't be transferred to the ground because of the spinning treadmill?

No. The treadmill matching the speed of the wheels ensures that the wheel hubs will not move in relation to the ground. Unless the landing gear breaks, this means that the plane will not move in relation to the ground.

**Buck** · 06-04-2009, 03:45 PM

Quote:

Originally Posted by MagicHef

Independently, I agree. But the sum of the wheel speed and the treadmill speed determine the plane's speed.

I also think that momentum and inertia may have something to do with it. The original question didn't ask if the plane is moving when the treadmill started up, or if they started at the same exact time and kept the same exact speed throughout.

MagicHef · 06-04-2009, 03:46 PM

Quote:

Originally Posted by cdcox

Well you could design bearings that had more friction, but that would then be the bearings that was keeping the plane from taking off instead of the treadmill.

It doesn't depend on the design of the bearings, as long as they are not ideal frictionless bearings. Yes, it would be the friction from the bearings keeping the plane from taking off, but the friction force only exists due to the speed at which the wheel is spinning, which is caused by the design of the treadmill.

Frosty · 06-04-2009, 03:47 PM

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.

06-04-2009, 10:15 AM
Jenson71 fides quaerens intellectum Join Date: Oct 2003 Location: United States Casino cash: $8330900	Something amazing to tell you concerning physics and motion 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.
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06-04-2009, 03:37 PM	#244
Fish Ain't no relax! Join Date: Sep 2005 Casino cash: $-1381081	__________________
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06-04-2009, 03:39 PM	#246
Buck Take a Chill Pill Join Date: Nov 2006 Location: South Carolina Casino cash: $6040295	Here is my postulate. A 747 cannot take off without moving forward relative to the ground, however the speed at which its wheels spin on a treadmill do not have any affect on the 747 moving forward.
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06-04-2009, 03:47 PM	#255
Frosty Go Beavers! Join Date: Jan 2001 Location: Washington Casino cash: $3398243	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.
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