# Friction

In this unit, students use propeller cars to explore the science phenomena of forces. They investigate action-reaction forces and see if a propeller car travels farther when its rubber band releases a smaller or larger force. Students then explore how friction affects motion by testing how far their car moves after rolling over smooth and rough surfaces. This page highlights elements of this lesson focused on friction.

## Science Background for Teachers:

The science background section provides teachers with more detailed information about the science phenomena being studied. In this unit, students explore how all motion in the world happens because of forces.

Energy is never created or destroyed, but it can be changed from one form to another. It can also transfer into or out of an object or system by force. Friction is one way that energy is transferred out of a system because it turns the kinetic energy of a moving object into heat. Friction is why your hands feel hot after you rub them together.

Some friction is helpful. You couldn’t walk without some friction. This is why it is hard to walk on ice. Ice is so smooth that there is very little friction between the ice and your shoes.

Car tires also need some friction to move. Car tires have deep grooves called treads, and they make the tire surface rougher. This helps the tires grip the pavement so they can move. Like car tires, running shoes have treads to make the bottom of the shoe rougher so there is more traction (friction) between your shoe and the ground.

## Science Lesson: Exploring Friction in Motion

Students build on their knowledge of forces and motion in this lesson with an investigation into how friction affects an object’s motion. They carry out an experiment to test how smooth and rough surfaces affect the distance a propeller car moves after rolling over each surface.

## Science Big Ideas

• An object can only change its motion when a force is applied, and energy is needed to provide force.
• Friction is a force that slows motion when two objects rub against each other by turning motion energy into heat.
• Some surfaces produce more friction than other surfaces.

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## Science Essential Questions

• Why do your hands get warm when they rub them together?
• Why do your hands have energy?
• How does the energy of your hands change when you rub them together harder or faster?
• How is rubbing your hands together similar to sliding down a slide?
• Have you ever tried walking on ice? If so, what happened?
• Why is it hard to walk on ice?
• Why are grass and pavement easier to walk on than ice?
• Would it be easier to push an object across a rough surface like grass or a smooth surface like ice?

## Common Science Misconceptions

Misconception: Objects at rest have no forces acting on them.
Fact: There are forces acting on everything on Earth at all times. For example, when you stand on the ground, gravity pulls you toward the center of Earth. In reaction, the ground has its own force that pushes back with an equal and opposite force.
Misconception: Forces do not always come in pairs.
Fact: Forces always come in pairs. These are called action-reaction forces—for every action, there is an equal and opposite reaction.

## Science Vocabulary

Action : a change caused by force; moving to a new place and going faster are two actions

Force : a push or a pull that acts on an object, changing its speed, direction, or shape

Friction : a force that slows motion when two objects rub against each other

Energy :  the ability to do work

Motion : the movement of an object from one place to another

Propel :  to push forward

Reaction :  an action that occurs as a result of another action

Work : any change in position, speed , or state of matter due to force

## Lexile(R) Certified Non-Fiction Science Reading (Excerpt)

Warming Up

Mariana forgot her gloves one morning. Her hands got cold. She rubbed them together quickly. Before long, her hands started to warm up.

Mariana’s hands became warm because of a force called friction. Friction occurs whenever two objects rub against each other.

Motion Energy

Friction turns motion energy into heat. Energy is the ability to do work. Work is any change in position, speed, or state of matter due to force.

All moving objects have energy. You use energy to rub your hands together. When you stretch a rubber band, you use energy to move your hands apart. This stores energy in the stretched rubber band. That energy changes back to motion energy when you release the rubber band.

Energy and Forces

Energy is needed to provide force. If a rubber band is stretched enough, it has the energy to provide enough force to move an object.

When you rub your hands together, each hand pushes on the other hand. These are action-reaction forces. The more force you use to rub your hands together, the more energy you use.

## Hands-on Science Activity

In this lesson, students use their propeller cars to carry out an investigation that tests how far it travels after rolling over a rough surface and a smooth surface. Then, students compare the distance their propeller cars traveled over the smooth surface (a transparency sheet) and the rough surface (felt). Students analyze the results of their experiment to describe, both verbally and in writing, what question they are seeking to answer, and how their investigation helps them answer it.

## Science Assessments

KnowAtom incorporates formative and summative assessments designed to make students thinking visible for deeper student-centered learning.

• Vocabulary Check
• Lab Checkpoints
• Concept Check Assessment
• Concept Map Assessment
• And More...

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