Can you generate electricity on a frictionless surface?
Answer:
[edit] Static friction
Static friction occurs when the two objects are not moving relative to each other (like a rock on a table). The coefficient of static friction is typically denoted as μs. The initial force to get an object moving is often dominated by static friction. The static friction is in most cases higher than the kinetic friction. Rolling friction occurs when one object "rolls" on another (like a car's wheels on the ground). This is classified under static friction because the patch of the tire in contact with the ground, at any point while the tire spins, is stationary relative to the ground. The coefficient of rolling friction is typically denoted as μr.
Limiting friction is the maximum value of static friction, or the force of friction that acts when a body is just on the verge of motion on a surface.
[edit] Kinetic friction
Kinetic (or dynamic) friction occurs when two objects are moving relative to each other and rub together (like a sled on the ground). The coefficient of kinetic friction is typically denoted as μk, and is usually less than the coefficient of static friction. From the mathematical point of view, however, the difference between static and kinetic friction is of minor importance: Let us have a coefficient of friction which depends on the sliding velocity and is such that its value at 0 (the static friction μs ) is the limit of the kinetic friction μk for the velocity tending to zero. Then a solution of the contact problem with such Coulomb friction solves also the problem with the original μk and any static friction greater than that limit.
Since friction is exerted in a direction that opposes movement, kinetic friction usually does negative work, typically slowing something down. There are exceptions however, if the surface itself is under acceleration. One can see this by placing a heavy box on a rug, then pulling on the rug quickly. In this case, the box slides backwards relative to the rug, but moves forward relative to the floor. Thus, the kinetic friction between the box and rug accelerates the box in the same direction that the box moves, doing positive work.
Examples of kinetic friction:
Sliding friction is when two objects are rubbing against each other. Putting a book flat on a desk and moving it around is an example of sliding friction
Fluid friction is the friction between a solid object as it moves through a liquid or a gas. The drag of air on an airplane or of water on a swimmer are two examples of fluid friction.
Resistance is the atomic friction of an electronic circuit or device as an electric current flows through it.
According to the law of conservation of energy, no energy is destroyed due to friction, though it may be lost to the system of concern. Energy is transformed from other forms into heat. A sliding hockey puck comes to rest due to friction as its kinetic energy changes into heat. Since heat quickly dissipates, many early philosophers, including Aristotle, wrongly concluded that moving objects lose energy without a driving force.
When an object is pushed along a surface, the energy converted to heat is given by:
where
N is the normal force,
μk is the coefficient of kinetic friction,
x is the coordinate along which the object transverses.
Physical deformation is associated with friction. While this can be beneficial, as in polishing, it is often a problem, as the materials are worn away, and may no longer hold the specified tolerances.
The work done by friction can translate into deformation and heat that in the long run may affect the surface's specification and the coefficient of friction itself. Friction can in some cases cause solid materials to melt.
there is no such thing as a "frictionless" surface
sorry
true, frictionless surfaces dont exist, but theoretically, you cant stop the plane on the surface using the breaks. if you were to use magnets, you could stop the plane and generate electricity using the electrons inthe magnetic field.
Something similar is becoming common on roller coasters. See the wikipedia article below. The key point to pick up from the article is that, in a frictionless world, the brakes could never fully stop the coaster (or plane in this case), since the braking force is directly proportional to the speed. Hence, as the plane slows down, the braking force becomes less. You will need the assistance of some other force to bring the plane to a full stop. Small reverse thrusters on the airplane for use once the speed is sufficiently slow would suffice.
http://en.wikipedia.org/wiki/brake_run#m...
You can.
Consider the linear motor. You are accelerating an object by manipulating (throwing energy into) a bunch of magnetic coils.
Since you have the object already moving, you can do the reverse, take energy from the output of the linear motor (the one with the frictionless surface) as the object decelerates along it.
This would presumably be called a linear dynamo.
The point is that with the outputs open, nothing would happen, but if you placed a load on the outputs, energy would come out of the motor and that energy is being sapped from the kinetic energy of the object in motion. Thus slowing it down.
In DC motors, the equivalent effect is called back EMF. You can get a DC motor, leave its wires unconnected and spin it freely. Hook its wires through a load (say a small resistor) and you cannot spin it as freely, it will slow down faster and you may be able to feel the physical resistance.
The "frictionless" surface would, of course, not be the means of stopping the craft. As stated above, there is another force that is present. Others have called it EMF, but it is really "mutual magnetic induction."
For simplicity's sake, Maxwell's (attrb to MIchael Faraday) equations state that a moving (oscillating) magnetic field will induce a current in a wire; and conversly, an oscillating electic current, will induce a magentic field. The "mutual magnetic induction" occurs when the current in the wire induces a current in another wire within it's magnetic field which in turn, creates its own magnetic field and induces an opposite current (with less magnitude) in the first wire. Thus, you get "inductive resistance" which will cause your craft to slow down and eventually stop. So, for a short time, you will "create" (actually "induce") electricity.
If you want to keep the induced voltage up, you will have to keep your airplane moving -- likely from an outside force. (Darn, one more great idea at perpetual motion shot down -- no pun intended!)
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