A wooden block is kept on a polished wooden plank and the inclination of the plank is gradually increased. It is found that the block starts slipping when the plank makes an angle of 18° with the horizontal. However, once started the block can continue with uniform speed if the inclination is reduced to 15°. Find the coefficient of static friction between the block and the plank.

Friction topics include: Friction and its types, fluid and solid friction laws, limiting angle of friction, self locking screens efficiency, limiting friction, v thread, pivot and collar bearing and friction clutches. Kinetic friction is a mechanical force that resists movement between two surfaces that are in contact and either rolling or sliding. It's also known as dynamic friction.  Kinetic friction affects the performance and efficiency of machines.  The force of kinetic friction is μk times the normal force on a body. The coefficient of kinetic friction is denoted by the Greek letter... Show more

Friction topics include: Friction and its types, fluid and solid friction laws, limiting angle of friction, self locking screens efficiency, limiting friction, v thread, pivot and collar bearing and friction clutches.

Kinetic friction is a mechanical force that resists movement between two surfaces that are in contact and either rolling or sliding. It's also known as dynamic friction. 

Kinetic friction affects the performance and efficiency of machines. 

The force of kinetic friction is μk times the normal force on a body. The coefficient of kinetic friction is denoted by the Greek letter ``mu'' (μ), with a subscript ``k''. 
The formula for kinetic friction is F f = μ k F N. 

There are three types of kinetic friction:
1. Sliding friction: The friction experienced by a body when it slides over another body
2. Rolling friction: The friction experienced between surfaces that have balls or rollers between them 

3. Fluid friction

In practice, all mating surfaces have roughness, which causes friction. If the surfaces are smooth, friction is very less. Lubrication smoothens the mating surface by introducing an oil film between it. 

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