hmmm.... physics question for you guys....

[VitaminG]

Re: hmmm.... physics question for you guys....

why wouldn't there be wind moving over the wings? If we're getting enough thrust to push the play 300mph, what's stopping it from moving forward and for air to move over the wings to generate lift?

If the OP had said there was "a tether attached to the tale and the plane was generating X amount of thrust, would it lift off?", I could see where you were coming from. But what in the question supports the notion that the play could NOT move forward if it was sitting on a big-ass conveyor belt?

[Newc]

Re: hmmm.... physics question for you guys....

Gary, you're not making sense. The wheels MUST turn in order to allow the plane to move. They are not the DRIVING FORCE, but they are equally important. If the wheels don't turn, the plane doesn't gain forward momentum which is the primary source of air flow.
If the wheels turn but are matched in speed by the surface they contact (i.e. the belt, oil slick, steel pellets, baby slobber), the plane's engines can generate all the thrust they want, but the plane will not move forward enough to generate air flow needed to lift.

[LouSiffer]

Re: hmmm.... physics question for you guys....

Well, as stated before, there is no wind to generate lift. The thrust of the engines help push the plane to gain lift. It is not the thrust that makes lift on a standard plane. Lift is the by-product of wind moving over and under the wings from forward momentum. If you put wings on a car and got it going fast enough, it would generate enough lift to get airborn, however, since the wheels are no longer in a surface to keep the momentum going, you will lose lift. Let's look at it this way:

1: Plane thrust is set to where if the plane was on a runway, it would travel 100 MPH.

2: For our experiment, the plane is on a conveyor that is traveling in an opposite direction of exactly the same speed. This causes no movement in the plane whatsoever....therefor no lift can be created since there is no wind passing under and over top of the wings. The plane is stationary.

The wheels have no affect as they are just a neutral part of the equation. Forward motion is forward motion whether it is wheel driven or jet driven. The wheel speed by the way,in my example, would be 100MPH....not 200 MPH. It is covering the the same amount of distance in the same amount of time. If the conveyor was moving at 100 MPH ,but, the planes thrust was set at 200 MPH, the wheel speed would then be 200MPH, but, the overall momentum of the plane would still only be 100 MPH.-Lou

[Number Of The Priest]

Re: hmmm.... physics question for you guys....

First, we have to know the aerodynamics of the turdloaf compared to the bullet so that we can determine whether it will accelerate downward due to gravity at the same speed that the bullet accelerates due to it being fired out of the gun. But, because gravity is constant, it will CONTINUALLY accelerate the turd until splashdown, whereas the air will slow down the bullet gradually.

Acceleration (gravity) = Change in velocity over Time. Acceleration is 9.8m/s on earth but we don't know the speed of the turd upon splashdown. So this question is a little difficult to answer... [img]/images/graemlins/laugh.gif[/img] [img]/images/graemlins/laugh.gif[/img] [img]/images/graemlins/laugh.gif[/img]

[Soap]

Re: hmmm.... physics question for you guys....

Hmmnn, the day you can take pearl from my hand grasshopper is the day you can leave.

Wax on wax off, Daniel son.

[Number Of The Priest]

Re: hmmm.... physics question for you guys....

Lou just brought up a very good correction. The plane's wheels are, in fact, turning the same magnitude of speed of the plane. I completely forgot about that.

[Soap]

Re: hmmm.... physics question for you guys....

Thanks, I love you man, no you can't have my beer.
This is truly a wonderful place at times.
Thanks for tolerating me.

[VitaminG]

Re: hmmm.... physics question for you guys....

Newc, I never said the wheels weren't turning. You might've missed my second-to-last post where I stated that if the plane and belt were moving at the same speed in opposite directions, the only effect on the wheels would be that they would spin twice as fast.

Lou, I get what you're saying & it would make sense if the jets were using the ground to pushing the plane forward. But since a jet expels exhaust behind it to push against the surrounding air to make it move forward, the movement of the belt is a non-factor. If the plane used some force against the ground to generate forward movement (like your flying car analogy) your argument would be valid. But since the surface the plane sits on has no bearing on its ability to move forward, the movement of the surface it sits on doesn't come into consideration.

[VitaminG]

Re: hmmm.... physics question for you guys....

if I were to run on a treadmill at say, 10mph and the belt were set to the same speed, I would run on the spot.

but if I wore a jetpack blasting away with enough power to move me forward at 200mph, and I stood on the same treadmill (now set to 200mph) on roller skates, what's to stop the jetpack from pushing me (spectacularly) off the end of the treadmill?

[zeegler]

Re: hmmm.... physics question for you guys....

You guys are totally overcomplicating this. The conveyor belt has no effect on the plane other than the minimal friction caused by turning the wheels faster. When an airplane sets off down the runway, the wheels are turning freely, and the thrust of the propellor or jet engine is acting against the air, and nothing else. That is simple fact, and you can argue all kinds of other fanciful reasons why it wouldn't take off, but the fact remains that it will.

[LouSiffer]

Re: hmmm.... physics question for you guys....

Again, the thrust does not cause flight, it helps promtote it , but, it needs the help of lift. You can only gain lift by wind running across the wings. If thrust was the sole proprietor of flight, wings would not be necessary. On the opposite end of the spectrum however, gliders fly and they do not have a jet. They solely use lift in the same manner a sail bot can glide forward into a headwind.

Thrust does use a "push" off a physical force to gain momentum. It is called air. By increasing the atmospheric pressure coming out of the nozzle of the jet, it uses the air behind it to push off of. Jet engines are nothing more than a fan on super steroids.-Lou

[Number Of The Priest]

Re: hmmm.... physics question for you guys....

Take a toy car to the supermarket next time. Shop for your groceries and line up at the checking aisle.

1.) Place the toy car on the conveyor belt when it moves and let go of the car completely. The car will move backwards as expected because nothing is moving the car.

2.) This time, grab the car. The fingers holding the toy car are the plane's engines pushing the car to go forward. When the conveyor belt activates, hold the car exactly where it is and you'll see the wheels turning at the same speed of the conveyor belt. They wouldn't move twice as fast. They'd only move twice as fast if your fingers (the jet engines) pushed the toy car along at that same speed.

[VitaminG]

Re: hmmm.... physics question for you guys....

yea, I get that Lou.

But as zeegs says in the post just above yours, the wheels are turning freely, so they have no effect on whether the plane will move forward. If the plane moves forward, wind passes over the wings, lift is generated. The ground surface that the plane rests on, moving belt or not, doesn't factor in to the jet or propeller's effect on the surrounding air.

[RobRR]

Re: hmmm.... physics question for you guys....

The plane will move and take off. The wheels only support the plane, they have no driving force. The plane moving has nothing to do with the wheels other than support. Now obviously the wheels will move at twice the speed, but beigns that the wheels have NO DRIVING FORCE AND OFFER ALMOST ZERO DRAG, it will not affect the plane.

To all the people who say the plane will not move, take the same scinario, but let the conveyor belt run in the oposite direction as the plane is landing... as soon as the plane touches the conveyor, will the plane instantly stop? If you said yes to that, I think you need to go back to elementary school. [img]/images/graemlins/laugh.gif[/img]

[LouSiffer]

Re: hmmm.... physics question for you guys....

[ QUOTE ]
if I were to run on a treadmill at say, 10mph and the belt were set to the same speed, I would run on the spot.

but if I wore a jetpack blasting away with enough power to move me forward at 200mph, and I stood on the same treadmill (now set to 200mph) on roller skates, what's to stop the jetpack from pushing me (spectacularly) off the end of the treadmill?

[/ QUOTE ] If the tread mill were moving at 10 MPH, but, you were moving at 200 MPH in the opposite direction, your momentum would overpower that of the tread mill. You would in fact be moving at 190 MPH until you run out of treadmill, then you would be moving at 200 MPH.

You ever see those movies where they drive a car onto the back of the moving truck? Well, lets say the truck is moving at 60 MPH. The car has to obviously be going faster that the truck to gain ground on it. However, once the drive wheels hit the ramp, they must slow down. If the do not, the car speed would be geater than the trucks and run through the front of it. The truck is moving 60MPH on a stationary object ( Street ). The car is doing 65 MPH on that same object ( street ). Once the car is on the truck, the truck becomes the stationary object the car travels on. This makes the cars overall speed 125MPH ( If you were standing still and hitting it with a radar gun ) in my example. However, if you were on the same truck and clocking the car, its speed would be 65 MPH since you are now being propelled forward at 60 MPH by the truck. -Lou