Dynamics - Friction

Slide text: Return to Table of Contents Friction
There are many different types of forces that occur in nature, but perhaps none is more familiar to us than the force of friction (F fr ). Friction - A Resistive Force Friction is a resistive force that opposes the motion of an object. What does sandpaper have to do with friction?
Friction is the reason objects stop rolling or sliding along a surface. It is the reason it is difficult to start pushing a heavy box along the floor. Friction - A Resistive Force There are many different types of friction: Friction between solid objects and air is often called air resistance. Friction between two fluids is called viscosity.
Where does friction come from? On a microscopic scale, most surfaces are rough. This leads to complex interactions between them that we don't need to consider yet, but the force can be modeled in a simple way. Kinetic Friction Force v
Kinetic Friction Force Friction that acts on an object that is already in motion is called kinetic friction . For kinetic -- or sliding -- friction, we write: Kinetic friction is the product of two things: μ k is called the coefficient of kinetic friction, and is different for every pair of surfaces. F N is simply the Normal Force, which, on flat surfaces, is equal to the weight of the object.
A man accelerates a crate along a rough surface. Draw the crate's free body diagram: Determine Σ F in the x and y directions F N mg F app F fr a