# Nonconservative Forces: Examples & Effects Video

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• 0:05 What Is a…
• 0:54 Path Dependence
• 1:45 Frictional Forces
• 4:16 Lesson Summary
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Lesson Transcript
Instructor: Damien Howard

Damien has a master's degree in physics and has taught physics lab to college students.

Find out what exactly it is that makes a force nonconservative. Then look at some of the most common types of nonconservative forces and how they affect the world around us.

## What Is a Nonconservative Force?

As a child, you probably spent some time on playgrounds. Every once in a while, you would run across a slide that you just couldn't slide down. Instead of having a quick ride down it, you would have to slowly scoot your way to the bottom. What was stopping you from sliding down is a force called friction. This force is an example of a type of force we call a nonconservative force.

In a nonconservative force, the energy within a system is not maintained, but is instead dissipated out of the system. For this reason, these forces are also known as dissipative forces. One common way this energy is dissipated is through heat, and friction is a good example of this. You can experience this yourself by simply taking your hands and rubbing them together. The heat you will start to feel is the energy being given off by the friction between your two hands.

## Path Dependence

One way we can tell that a force is nonconservative is to see if it is path dependent. Unlike with conservative forces, the work done by a nonconservative force on an object depends on the route the object travels. To understand this, let's imagine you're pushing a box across a floor from one side of the floor to the other at a constant speed. Would you rather push the box in a straight line or in a zig-zag pattern? Most people will choose to push the box in a straight line. They know instinctively that this will take less work than the zig-zag pattern, but why is that? That's because to keep the box moving at a constant speed, you are fighting against friction. The box that travels the longer path has to fight against more friction. Since more friction acts on the box on the zig-zag path than the straight path, this means that friction is a path-dependent force.

## Frictional Forces

We've talked a lot about friction so far in this lesson, and that's because it's the most common nonconservative force. However, friction is not a one-size-fits-all force. There are different types of friction for varying circumstances. In fact, in our example, the box being pushed along the floor is experiencing several different kinds of friction at once.

The first type of friction our box encounters is static friction. This is the frictional force that opposes putting an object into motion. For our box, static friction is acting between it and the floor before it starts being pushed along. In other words, you have to overcome static friction to get the box moving.

Once the box has started moving, the type of friction switches over to kinetic friction. Kinetic friction is the frictional force that attempts to slow an object that is already in motion. Most often, this force acts in the direction opposite to the object's movement. This force started acting to slow the box once it got moving, and the person pushing it must constantly overcome it to keep the box from stopping.

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