# Friction: Hard to Live With, Can't Live Without

Contributor: Jay Gregorio. Lesson ID: 13205

On a rainy day, drivers are always reminded to slow down. While it's true that the road is slippery when wet, there is more to that! Learn about friction and discover its advantages and disadvantages!

categories

## Physics

subject
Science
learning style
Kinesthetic, Visual
personality style
Beaver
Grade Level
High School (9-12)
Lesson Type
Dig Deeper

## Lesson Plan - Get It!

Audio:

You may have heard someone use the word friction to describe people who aren't getting along well with each other.

When someone says there is friction, they mean there is disagreement, opposite beliefs, misunderstanding, or miscommunication. If not resolved, friction among team members can be damaging and disastrous.

The idea of friction in the above context is similar to how it is defined in science. In physics, friction is the force between two surfaces in contact.

In this lesson, you will discover that friction is always present no matter how smooth these surfaces may seem. You will also learn that this important science concept has many applications in your everyday life!

What Is Friction?

Friction is defined as a resisting force when two surfaces in contact rub against each other or slide past each other.

Surfaces of different materials may look and feel different. Imagine running your fingers across the sandpaper surface, then compare it with the glass surface.

• Which one feels smooth? Rough?

Your sense of touch will agree that the glass surface feels smooth and the sandpaper feels rough. These two surfaces offer different amounts of friction when they are in contact with or slide past another surface — your skin.

The direction of this force is always opposite to the object's motion or attempted motion — conditions where friction is present. You will learn about the difference between these conditions in this lesson.

But first, look at the example below, where a crate is pushed across a concrete surface.

Notice that a tiny contact area between the wooden crate and the concrete pavement across which it is moving is magnified in this diagram. Look closely at each surface; you can see they are not smooth!

Wood and concrete both feel rocky or rough. The rocky surfaces lock into each other when they are in contact, making it challenging to slide past each other.

Now, imagine we slide this wooden crate across the ice.

• Will it be easier to move the wooden crate this time? Why or why not?

You are correct if you said it would be easier. The ice surface is much smoother than concrete pavement. Less rocky surfaces make it easier to slide past each other.

Friction Meets Misconception

Take a look at the above diagram again.

Imagine you are the green force arrow pushing the crate to the right across the concrete pavement. Let's say the crate did not move, no matter how hard you tried.

• Do you think friction remains if the crate does not move?

The answer is yes!

This is a common misconception about the force of friction. Many people think that since one object did not slide past another, there should be no friction.

This is wrong! Whenever there is an attempt for two surfaces in contact to slide past each other, there is friction.

• Why is this so?

You already know that the surfaces of the wooden crate and the concrete pavement are not smooth. Since the wooden crate is heavy, the two rocky surfaces press hard against each other, making the locking-in of the surfaces stronger. This is shown by the gravity arrow in the image.

Therefore, sliding past each other requires much more pushing force from you!

The crate will start moving if your push can overcome these surfaces locking in. We know the surfaces sliding past each other makes the friction force more evident.

Friction: Advantages and Disadvantages

The force of friction is present in our everyday lives; however, you may not notice it most of the time!

Look at the following examples and discover how high friction forces have advantages and disadvantages! We cannot live without friction, even though it can also be hard to live with.

Soles of Your Shoes

There are specific types of shoes for different activities and surfaces. These different designs were created not so much to look fashionable but to be more functional.

You may have running shoes, but you wear a different pair during winter when the ground is slippery.

The soles of your shoes differ from one another, but most are made of rubber. Rubber is a material that offers high friction. Try sliding rubber against the concrete surface; you will see how difficult it is.

Designing a shoe sole to create high friction is an advantage that keeps you safe.

Ice Skates

Not all footwear benefits from high friction. Ice skates are different because high friction is a disadvantage!

In this situation, metal blades and ice are the two surfaces in contact. You already know that ice is a slippery surface, which means it has less friction.

The blades of the ice skates are made to skim over the ice so that they melt a little, making them more slippery. When this happens, the ice skater moves smoothly with grace and speed!

In the Got It? section, review the basic concepts of friction force and explore other examples of the application of friction force!

• Are you ready?
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