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 used 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 members of any team can be damaging and disastrous.

frustrated team

The idea of friction in the context described above has some similarities with how it is defined in science. In physics, friction is about the force that exists between two surfaces that are in contact with each other.

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

What Is Friction?

Friction is defined as a resisting force that is present when two surfaces that are 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 surface of sandpaper, then compare it with the surface of glass.

  • 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 - in this case 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, let's take a look at the example below where a crate is pushed across a concrete surface:

crate friction

Notice that one small contact area of the wooden crate and the concrete pavement across which it is moving is magnified in this diagram. Look closely at each surface, and you can see they are not smooth at all!

Wood and concrete both feel rocky or rough. The rocky surfaces have the tendency to lock into each other when they are in contact and, therefore, make it difficult to slide past each other.

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

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

If you said it would be easier, you are correct. The ice surface is much smoother than concrete pavement. Surfaces that are less rocky 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 pushed.

  • Do you think friction is still present if the crate does not move?

The answer is yes!

This is a common misconception about the force of friction. A lot of people think that since one object did not slide past another object, 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 a lot more pushing force from you!

If your push is able to overcome these surfaces locking-in, then the crate will start moving. We know the surfaces sliding past each other makes the friction force more evident.

Friction: Advantages and Disadvantages

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

Take a look at the following examples and discover how high friction forces have some advantages and disadvantages! Friction actually is something we cannot live without even though it can also be hard to live with.

Soles of Your Shoes

footprints

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, and you will see how difficult it is.

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

Ice Skates

ice skates

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

In this situation, the two surfaces in contact are metal blades and ice. 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, we'll review the basic concepts of friction force and explore other examples of the application of friction force!

  • Are you ready?

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