How are airplanes able to fly & boats able to float?
462882
an airplanes wings are shaped specially to create an upward force on them called "lift.'\n\nessentially, it forces air to flow over top of them, which creates negative pressure on the top side of the wings, causing the plane to "float" on top of the air, but only when going faster than certain speeds.\n\nA boat floats because it displaces more water than its own weight, causing it to be less dense then the water, and making it float on top.
481877
Your other answerers are on the right track.  When a boat floats, it displaces a volume of water with a weight equal to the weight of the boat.\n\nSo, the heavier the liquid in which the boat is floating, the less liquid it must displace in order to float, and thus, the higher it will float.\n\nThis means that the basic question is which is more dense (and so, heavier), saltwater or freshwater.  And, the answer is that saltwater is somewhere between 2.5% and 3.5% more dense than freshwater.
730217
What limits the altitude of an airplane has nothing to do with how much fuel it has.\n\nIt has to do with the type of engine it has, and the maximum speed it can obtain.  \n\nBoth propeller and jet engines need air .... both because they need oxygen to burn the fuel, and because they work by pushing air backwards.\n\nSo every airplane will reach a height at which it doesn't have enough air to go any faster ... at that point it can't go any higher.\n\nAs far as momentum carrying you further, this is determined by the maximum speed of the airplane.  To go further up, you need to have enough force in the engine to counteract the force of gravity.  To keep going indefinitely, you need enough force to reach the escape velocity determined by the amount of gravity of the earth ... and that is a *huge* velocity.  Even the Space Shuttle rocket can't get the Space Shuttle out of the earth's orbit.  \n\nThat's why it takes an *enormous* rocket like the Saturn V to get a small ship like the Apollo spacecraft out of the earth's orbit on its way to the moon.  Once in space, its rockets work without oxygen because they carry their own oxygen with them for fuel (something an airplane does not do).
294601
Simply put, faster air moving over the top of the wing creates a lower pressure than the slower air under the wing.  This creates lift and causes the wing and the plane to rise.\n\nThe shape of an aircraft wing is curved on the top and flat on the bottom, the air has to move further on the top of the wing in the same time, so it moves faster creating lower pressure. \n\n(This is Bernoullis principle, higher speed = lower pressure, lower speed = higher pressure).  \n\nThe plane is propelled by a jet engine or propellor fast enough until lift is achieved.
108792
They are made of wood, which floats because it has a lower density than water.  If you made a ship out of solid gold, it would sink, for example.
746359
Why does a bird fly?  A fish swim?
901376
Buoyancy is alot like drag in air, its proportional to surface area. (As in, if you increase the surface area, the force required to overcome the "drag" of water increases).\n\n You have one of two situations: Your boat is stationary, in which case, a barge or square shaped vessel with pontoons balancing it, or a dynamic vessel, with pointed fore and aft sections, once more with pontoons.\n\n Pontoons are what are going to make or break your design, you can increase your potential surface area by adding pontoons on arms, jutting from the sides of your vessel, and reduce your boat's mass at the same time.
506884
This design cant pull enough air down fast enough to achieve lift. The key to flight is the airfoil shape of the wing or helo propeller. Its naturally causes high pressure under the airfoil as air moves rapidly over it. Thats where lift is achieved.
1134473
The Sea. The sea can make a ship float but not a pin.
24445
An airplane flies due to the aerodynamic reactions that happen when air passes at high speed over the wing.\n\nWhen air passes over the wing, it is forced to pass underneath or over top of it. The length of the wing is larger on the top portion, so according to laws of aerodynamics, the air flow becomes faster, to compensate the larger distance to be travelled. This significantly diminishes the pressure of air on the wing; the difference of pressure under and over the wings creates the necessary lift for flight.\n\nAlso they obey, on a smaller scale, the laws of inertia as formulated by Isaac Newton: a force acting in one given direction tends to be balanced by another force with same intensity, and of opposing direction. As the wings of the airplanes tend to make curve for low, a air flow is created in this direction and, as consequence, the airplane receives a push from same force in the opposing direction.\n\nAirplanes need a high speed so that the difference of the pressure of air under and over the wing is enough for lifting the aircraft. To reach these high speeds, an airplane needs to cover a certain distance on the ground, before reaching the speed needed for take-off. For larger and heavier aircraft it will generally require a longer runway to reach the necessary speed for the take-off, given the larger amount of energy needed.
102873
Archimedes Principle.  The bouyant force pushing up on an object in a fluid is equal to the weight of the fluid displaced by the object.  So as long as the ship displaces more than its weight in water, it will float.  This is why ships made of steel and other dense materials tend to be very big and hollow.
943222
Only if the plane has engines with sufficient thrust to hold it up against gravity, and it orients itself engines-facing-down to hold itself there -- the most recent jet fighter for the US Air Force can do this, as well as some "jumper jets", but not any other planes and certainly not any commercial airliners can.\n\nRelative to the ground, a plane can be "still" if the wind speed aloft is above the plane's stall speed.  In that case, air is moving across the wings of the plane at a fast enough speed to give enough lift to keep the plane aloft even though it doesn't move relative to the ground (the thrust from the engines and the "headwind" balance each other out).\n\nYou can get a good sense of this if you fly a lot between the pacific coast of the US and Asia -- the strong jetstream across the pacific does funny things to "ground" speed.  When flying west to east (with the jet stream), indicated ground speed on flights I've been on has exceeded 1,000 MPH, even though the plane can't go more than 400 MPH or so with no wind.  And flying east to west, indicated air speed will sometimes be as low as 50-60 MPH, even though airspeed is still 400MPH -- that headwind jetstream is a killer, and significantly lengthens the time it takes to get from LA to Tokyo (the normal 11-hour flight once took us 16 hours because of the headwind!) -- though I've made the return trip in under 7 hours!
50908
The shape of the wings is such that, as the aircraft moves forward, air flows over the top surface faster than the underside...  so the pressure above the wing is lower than the pressure under the wing...  thus, the force from under the wing is greater than the force on the top, and there is thus a net "lift" as the plane moves.
1137769
plane starts gliding...trading potential energy of its height to kinetic energy forward to hopefully find a landing site.  this is why airplanes gain altitude as quickly as possible after take-off, so if there is an engine problem they have time to find a landing place.\n\nIf thrust is lost, gravity and lift become unbalanced with gravity winning because altitude must be lost to maintain airspeed.  drag wins over thrust since there isn't any thrust so altitude must be lost to compensate for drag-thrust imbalance.\n\nsource: i'm a pilot
439796
Oil has less density than water so it floats.  When it's empty, air has less density than water.  Same thing.  Or it has to do with the displacement as mentioned below...
1162285
Aircrafts' wings gives the aircraft lift (i.e. shaped so that when wind passes through, it will be pushed up), and once a certain velocity is reached, the upwards lift is enough to counteract the forces of gravity (and exceed it), and thus they fly.\n\nSpaceships achieves escape velocity to escape from the Earth's gravitation (or at least far enough for the space ship to reach orbit). Then, at the orbit, it orbits earth at a certain velocity which gives it enough velocity to counteract the remaining attraction from Earth's gravity, hence it stays in space.
117781
Certainly possible in theory. I doubt if anyone has ever done it in practice.\n\n\nRemember that a plane stays up in the air because of the speed that the air moves over its wings, not beceuse of how fast the plane moves relative to the ground. If a plane turns into the wind it can generate the same lift while travelling slower relative to the ground. With a strong enough headwind it is quite possible for a plane to remain stationary and airborne\n\nBut as I said, this is only theoretically possible. I've seen light planes do this and hang-gliders and birds do it all the time. But it would be incredibly dangeorus for a 'passenger flight'. If the wind were to drop, even for amoment, the plane would immediately stall and fall from the sky. It's fairly easy for a light plane or glider to recover from such a stall, but a large commercial passenger craft would find it much harder. There's a good chance it would crash.