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Kinetic friction occurs when two surfaces slide against each other. It is an opposing force that resists the motion of the moving body. Imagine running your hand across a table; the force that makes it a little hard to slide your hand is the kinetic friction. This type of friction acts parallel to the surfaces in contact and opposite the direction of movement.
Kinetic friction is characterized by a specific coefficient, known as the coefficient of kinetic friction (\( \mu_k \)), a constant that varies based on the materials involved. This coefficient provides a measure of how "sticky" or "slippery" a surface is when in motion, allowing us to calculate the frictional force, which is crucial in solving many physics problems. The formula for kinetic frictional force is:

• \( f = \mu_k N \)

where \( N \) is the normal force. This indicates that frictional force depends on both the coefficient of friction and the normal force acting on the sliding object.

The normal force is a supportive force exerted perpendicular to the surfaces in contact. When an object, like our baseball player, is on a flat surface, this force acts upwards, balancing the gravitational force pulling the object downward. It's called "normal" because it is at right angles to the contact surface.In physics problems, especially those involving friction, calculating the normal force is often necessary. For a situation with no vertical acceleration, like our baseball player sliding on level ground, the normal force is equal in magnitude and opposite in direction to the gravitational force, \( mg \). This means the normal force \( N \) is given by:

• \( N = mg \)

This formula simplifies many friction calculations because it allows for quick determination of how strong the support from the surface is, which is fundamental to finding the frictional force involved.

The coefficient of friction is a dimensionless scalar value that describes the ratio of the force of friction between two bodies and the force pressing them together. In simpler terms, it measures how much friction force acts relative to the normal force. There are two main types: static and kinetic, but here we're focusing on kinetic friction.The coefficient of kinetic friction (\( \mu_k \)) tells us how rough or smooth the sliding surfaces are. High values mean more friction, requiring more force to slide an object, while low values indicate smoother surfaces that slide more easily. This coefficient is calculated using:

• \( \mu_k = \frac{f}{N} \)

In our exercise, we rearranged this equation to solve for \( \mu_k \) using known values for frictional force \( f \) and normal force \( N = mg \). This calculation allows us to determine how effectively the player's surfaces interact, giving us an insight into the nature of the materials and contact surfaces involved.