Originally posted by FabianFnas Only 'pretty much'?
I thought *every* movement starting with a accelleration is driven by the Newtons action-reaction thing?
Is there any other form?
Probably not, but I was just trying to avoid someone jumping in with "WRONG!! In this case, blah blah...". So I left in my get out clause 🙂
Originally posted by mtthw Probably not, but I was just trying to avoid someone jumping in with "WRONG!! In this case, blah blah...". So I left in my get out clause 🙂
Oh, I see. Smart move! 🙂
But either way:
Is there any way to induce movement to an object other than using the Newtonian action/reaction method?
Originally posted by FabianFnas Oh, I see. Smart move! 🙂
But either way:
Is there any way to induce movement to an object other than using the Newtonian action/reaction method?
The universe is a closed system and therefore any force created within it must be counteracted by a force equal and opposite also created. Therefore it is impossible to create a force without an equal force acting somewhere else.
Originally posted by mwmiller The plane is held on the ground by gravity.
Lift will overcome the force of gravity and allow the plane to fly.
Lift is created by relative motion between the wing surface and air.
In the treadmill example there is no relative motion between the wing and the air, so there is no lift.
Without lift, gravity wins.
After further thought on this, I believe the treadmill is irrelevant.
The plane engine will move the plane through the air and create lift as the plane is thrust forward. The treadmill will not prevent the plane from moving forward as long as the engine is creating thrust.
The wheels only allow the plane to roll more easily but they do not move the plane, as has already been pointed out. They will be caused to roll much faster than normal because the treadmill is moving in the opposite direction.
So in conclusion the plane will still fly once it develops enough lift, and the runway surface is irrelevant.
Originally posted by XanthosNZ The universe is a closed system and therefore any force created within it must be counteracted by a force equal and opposite also created. Therefore it is impossible to create a force without an equal force acting somewhere else.
I'm probably making a fool of myself, but what about gravity? Is it counteracted by anything?
Originally posted by Palynka Can you please explain how it is 'equal and opposite'?
Yes. The short answer is that the Earth is more massive, so the force affects it less than it affects a person for example, though the force is equal in both directions.
Originally posted by Palynka Can you please explain how it is 'equal and opposite'?
Newton's third law is that when one body exerts a force on another, the second body exerts a force on the first of the same magnitude, but in the opposite direction ('equal and opposite'😉.
With gravity, two bodies attract each other. The Earth pulls you towards it, but you pull the Earth towards you with exactly the same force.
Because the Earth is rather big, the force you apply on it doesn't have much of an effect.
Originally posted by mtthw Newton's third law is that when one body exerts a force on another, the second body exerts a force on the first of the same magnitude, but in the opposite direction ('equal and opposite'😉.
With gravity, two bodies attract each other. The Earth pulls you towards it, but you pull the Earth towards you with exactly the same force.
Because the Earth is rather big, the force you apply on it doesn't have much of an effect.
Does that help?
relative to mass.
I think if that was inserted anywhere in the last few posts then people wouldn't make the mistake if thinking you think that a human body can exert the exact same force as a bloody planet.
Originally posted by KingsBishop relative to mass.
I think if that was inserted anywhere in the last few posts then people wouldn't make the mistake if thinking you think that a human body can exert the exact same force as a bloody planet.
That's the point! A human exerts the same force on a bloody planet as a bloody planet exerts on a human! The gravitational force between two objects is proportional to the product of the two masses.
Originally posted by KingsBishop relative to mass.
I think if that was inserted anywhere in the last few posts then people wouldn't make the mistake if thinking you think that a human body can exert the exact same force as a bloody planet.
But the force is the same. The effect is different (thanks to F=ma) but the actual force is the same.
The plane will overcome gravity if it has an airspeed great enough to produce lift greater than the force of gravity. With a Cessna 172s, that is approximately 65 knots. Airspeed is different from ground speed, you need to factor head wind or tail wind.
Before the treadmill starts, I assume the plane is at rest with 0 wind. When the treadmill does start, inertia will cause the plane to lag behind, and then start backwards with the treadmill, due to friction. If you then start the propeller, the plane will start forward and will handle as if there is a tail wind until the airspeed of zero is reached. At that point the plane will be stationary in space, but wheels will be rolling with the treadmill.
The wheels on the plane can be rolling as fast as the treadmill, but that will not cause the plane to go backwards, because the plane has forward thrust thru the air. That is all that matters for lift off. Full throttle, elevator up, slight right rudder, off you go.
Originally posted by mlprior The wheels on the plane can be rolling as fast as the treadmill, but that will not cause the plane to go backwards, because the plane has forward thrust thru the air. That is all that matters for lift off. Full throttle, elevator up, slight right rudder, off you go.[/b]
And where is the airspeed coming from, you would be stationary at this stage. Therfore assumming no wind, you air speed will be 0kts.
26 Oct '06 10:09
Will the airplane fly?
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