So what if we tie the beam on the bottom of the boat ?? (meaning in the water but understill tied to boat)

The water level falls, the beam in the boat in order to float has to displace more volume than the the beam in the water which sinks.

Sharyn

Water level falls.

To keep afloat, the boat displaces 5 tons + boat weight of water.
Once the girder is in the water, it doesn't displace so much water (which is why it sinks) and the boat only displaces its own weight of watter (much less than at the start).

As a result, the watter level falls.

If the beam hits bottom and layes there, it doesn't matter, same result.

If the rope/chain is short and the beam is held in the water without touching the bottom, the boat (and beam) still need to displace their combined weight in water, so in this case, no change in water level.

As opposed to the case where the beam is tossed loose into the pool, the water level rises, for complex reasons. The amount of flotation the suspended beam generates, equals the amount of water it displaces. The boat floats lower in the water, because although it is relieved of supporting the part of the beam's weight that the beam's flotation supports, the boat is still supporting part of the beam's weight, and is displacing more water, raising the level in the pool. If the beam is sitting on the bottom, its weight, minus its flotation, is being supported by the bottom and is not pulling the boat down. In this latter case, the pool level falls, as opposed to when the beam was in the boat.

The Plane Will Not Fly
 

Very interesting ideas bouncing around, but the plane would not get off of the ground, based solely on the scenario.

Thrust, although it creates a suction at the intake and moves air through the engine, that air in no way creates lift.

To cause a winged aircraft to rise there must be lift. Lift is created by the air moving over and under the wing. This is done (absent of other influences) by forward movement.

In the scenario, AS STATED, no adds or creative influences, there is nothing present to create lift. Not the engine thrust, suction or pressure, the engine isn't a player (an aircraft could be pulled forward with a tieline and it would have lift), Not the conveyor belt, it reacts or actually COUNTERACTS any forward movement created by the engine.

There is no mention of wind tunnels, updrafts, downdrafts or any other thing that is moving wind in order to create lift.

If it was possible, for the airplane in this scenario to take off, aircraft would not need any runways at all. They would crank there engines, throttle up and away they would go.

I have had my hands on a operating F-16 (on the ground) at full throttle while performing maintenance, and I never saw one starting to float upward beacause of the "thrust". They go airborne when they move forward.

In the given scenario, with the boundaries applied, and the conveyor counteracting any attempt at forward movement, it is scientifically, and physically inpossible for the airplane to fly.

The wheels counteract the reverse motion of the conveyor belt by rotating at twice the speed.

The airplane will fly.

Why would they rotate at twice the speed? The opening post states that the belt matches the speed of the plane. In other words, the plane is stationary and no lift is created.

The belt matches the speed of the plane, in reverse, (that is key)! If the plane moves the belt moves and simply spins the wheels faster! The engines propel the plane forward and the wheels get spun faster by the belt. The belt makes no change to the actual forward speed of the plane. In fact if the plane does not move, the belt does not move!

Remember that the belt just turns the wheels, it does not actually move the plane at all.

It will fly!

Mike

hmmm
 

i think the plane would stay on the ground being that it would only reach half it's take-off speed before it runs out of runway.


Is there an actual answer?
Oh Yeah! Is there really a MENSA member in here?

It would reach it's full take speed, not half speed. Only the wheels get turned by the belt, the planes speed is not affected. Wheels Roll!

Mike

Hi Joel and welcome to DVinfo! Always nice to meet a fellow servicemember, past or present. I recently retired from the USAF and have been HOTAS in many jet aircraft, including the Block 52 F-16, both on the ground and in the air.

Well, I thought this riddle had run its course a while ago even though not everyone was convinced of the correct answer: the jet will fly. Richard and others have given the answer, but here it is again just stated in different words. When the burner lights, it doesn't matter if the ground does start rolling backwards (a la our imaginary treadmill), the wheels will just spin faster and you'll be going somewhere fast as all that thrust propels the jet. There'll be weight on wheels until flying airspeed is attained and enough lift is generated by the wings to climb, but the wheels spinning ever faster against the receding ground would not (in the theoretical world) impart drag to the jet to counteract the thrust driving it forward.

OK .... the plane takes off, it reaches full speed in the same distance and takes off. It will do this even if the belt/runway moves at double the speed of the plane, because the belt exerts no force on the plane to hold it back. The faster the belt moves, the faster the wheels spin, but the engines keep pulling the plane through the air. As they do, they bring the airframe (and wings) to take-off speed, the wings create lift, the plane lifts off.

The wheels are spinning like crazy, because the plane is moving forward and the "ground" is moving backward, but the wheels are not holding the plane back, the plane is not prevented from moving forward like it would be restrained for a maintenance situation.

To demo this for yourself...
Tie some string to the front of a toy car (or toy plane with wheels). Bring this to the nearest treadmill.
Put the toy on the belt, hold the string and crank up the treadmill speed.
Note that regardless of how fast the belt is moving, you can still pull the toy forward as fast as you like by tugging on the string. You pulling on the string is the same force as the engines pulling/pushing air.

Yes, there's a little extra friction to overcome, but it's really almost nothing in relation to the thousands of pounds of force that these engines are capable of producing.


PS: Just wanted to add a very heartfelt thank you to Pete, Joel and every other past and present service member here!

I don't know how to make it any clearer.

The engines generate forward thrust ON THE AIRFRAME.

In order to counteract the forward thrust, and 'keep the plane stationary'... the 'conveyor belt' runway must exert EXACTLY THE SAME THRUST in the oposite direction ON THE AIRFRAME..

The belt only touches the airplanes wheels.

The wheels ROTATE in order to eliminate the drag of the runway. They do this at whatever speed the plane is moving forward and the ground is moving 'backwards' in relation to it.

IF the belt were moving backwards at three times the forward velocity of the airplane, it would still not exert enough 'drag' to stop the aircraft, the wheels would simply rotate faster. Sure, a little more heat and friction in the wheel bearings, but not enough to stop the aircraft.

The plane will fly.

And this is absolutely my LAST posting since I first posted the answer.

is it that serious? lol. I thought the Conveyer belt was turning in the same direction as the the plane was to be moving.