what is friction? please help...?

Answer 1

rubbing 2 things together to create heat.
Rub yor hands together really fast and see what happens.

Answer 2

Friction is a force which causes deceleration or negative acceleration in a body in motion. All earthly bodies in motion is subject to friction.

Answer 3

Friction is a force that opposes the motion of a body.
The force of friction comes due to molecular interlocking.

Answer 4

Friction is the force that opposes the relative motion or tendency of such motion of two surfaces in contact. It is not, however, a fundamental force, as it originates from the electromagnetic forces and exchange force between atoms. In situations where the surfaces in contact are moving relative to each other, the friction between the two objects converts kinetic energy into sensitive energy, or heat (atomic vibrations). Friction between solid objects and fluids (gases or liquids) is called fluid friction. See also aerodynamics and hydrodynamics. Friction is an extremely important force - for example, it propels automobiles and other ground transport and holds nails, screws and nuts.

Types of friction
Frictional force in mechanics is the force which opposes the relative motion of an object. It is directed opposite to the motion of an object.

There are three types of frictional forces.

Static friction is the friction acting on a body when the body is not in motion, but when a force is acting on it. Static friction is the same as the force being applied (because the body isn't moving). Static friction acts because the body tends to move when a force is applied on it.
Limiting friction is the friction on a body just before it starts moving. Generally, limiting friction is highest.
Kinetic friction is the friction which acts on the body when the body is moving. Kinetic friction is usually smaller than limiting friction.
The kinetic frictional force of a solid-solid interface is given by:


where R is the normal reaction force acting between the interface and the object and is the coefficient of kinetic friction. The value of the coefficient depends upon the nature of the surfaces.

The limiting friction is given by


where R is the normal reaction force acting between the interface and the object and is the coefficient of limiting friction.

For a fluid, the frictional force is directly proportional to the velocity of the object.


[edit] Static friction
Static friction occurs when the two objects are not moving relative to each other (like a book on a desk). 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 always exerted in a direction that opposes movement, kinetic friction always does negative 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.

http://en.wikipedia.org/wiki/Friction

Answer 5

Hi. A force which tends to prevent motion of one substance against another. Rubber has higher friction than grease.

Answer 6

definition of friction:

friction: the force between two surfaces rubbing together

hope this helped you.

Answer 7

when 2 rub against each other and create heat. like when you rub your hands when you are cold.