How many kinds of friction

Swimmer in water demonstrating friction. Different Types of Friction When it comes to forces, friction is one of the first that comes to mind. Fluid Friction When you hear fluid friction , friction in water might come to mind. External friction is the friction force when solid moves through it. Internal friction is the friction of the molecules themselves in the fluid. Explore a few examples to see fluid friction in action.

Rolling Friction The example of the ball rolling down a hill is an example of rolling friction. Throwing a Skee-Ball Rollerblading down the street Rolling a bowling ball down the lane Car rolling down the road Rolling down the street on a skateboard. Puck moving across the ice in hockey Kicking a book across a floor Dragging a sled up a hill Dragging your body across carpet Foot dragging against a sidewalk. Examples of static friction are aplenty. Book resting on your end table Plant resting on a counter Shopping cart resting in the cart corral Dresser sitting on your floor PlayStation sitting on your entertainment center.

Sliding Friction It is the friction that acts on objects when they are sliding over a surface. Sliding friction is weaker than static friction.

This friction slows the rolling wheels so you can stop. Rolling Friction It is the friction that acts on objects when they are rolling over a surface.

It is much weaker than sliding friction or static friction. This explains why most forms of ground transportation use wheels, including bicycles, cars, 4-wheelers, roller skates, scooters, and skateboards. For example: The ball bearings in this wheel reduce friction between the inner and outer cylinders when they turn.

Fluid Friction Fluid friction is friction that acts on objects that are moving through a fluid. A fluid is a substance that can flow and take the shape of its container.

Fluids include liquids and gases. Another example could be a swimmer, cutting through the edges of water where the water provides fluid resistance to the swimmer. A low value of the coefficient of friction indicates that the force required for sliding to occur is less than the force required when the coefficient of friction is high. The value of the coefficient of friction is given by. Where, F is the frictional force and, N is the normal force.

Derivation for coefficient of friction Perpendicular force reduced When an object is placed on an incline, the force perpendicular between the surfaces is reduced, according to the angle of the incline. Friction is the resistance to motion of one object moving relative to another. It is not a fundamental force, like gravity or electromagnetism. Instead, scientists believe it is the result of the electromagnetic attraction between charged particles in two touching surfaces.

Scientists began piecing together the laws governing friction in the s, but because the interactions are so complex, characterizing the force of friction in different situations typically requires experiments and can't be derived from equations or laws alone.

For every general rule about friction, there are just as many exceptions. For instance, while two rough surfaces such as sandpaper rubbing against each other sometimes have more friction, very smoothly polished materials such as plates of glass that have been carefully cleaned of all surface particles may actually stick to each other very strongly.

There are two main types of friction, static friction and kinetic friction. The easiest way to understand the three frictions is to take a smooth board, a wooden block, and a marble. Place the wooden block and the marble on the board while it is level, and then gently raise one end of the board.

The marble will begin moving almost immediately, demonstrating that its rolling friction is very low. The difference in height between the two ends of the board will have to be considerably greater before the block begins to move. Once you have determined how large an angle it takes to start the block sliding, raise the end of the board to that point, then, after the block has started to slide, lower the high end of the board slightly. The block will continue to slide, because sliding friction, the friction between two surfaces that are moving relative to each other, is always less than starting friction, the friction that must be overcome to start motion.

Applying this to a car on ice takes one more definition: the effective rolling friction of a car's wheels involves not only the rolling friction of the wheel itself, but also the various sliding and rolling frictions of the brakes and bearings.

For a car to start moving, the engine must apply enough force to overcome the internal friction of the transmission and bearings and start the wheels turning, but it must do so without letting the wheels apply so much force to the road that they overcome the starting friction of the wheels on the road and start spinning.