Essential Questions

What is a force? What are the different kinds of forces? What is friction? How can friction be increased or

decreased?

For 800 years the Leaning Tower of Pisa has been tilted. Located in Italy, officials worried that it would fall over. What forces are acting on the Leaning Tower of Pisa?

When you jump up in the air, what pulls you back down to Earth?

What pulls a magnet together or pushes it apart?

The answer is….

A FORCE is a push or pull that causes changes in motion.

Forces can affect motion in several ways:

→ They can make objects start moving. → They can make objects move faster. → They can make objects move slower. → They can make objects stop moving. → They can make objects change

direction.

Forces Nothing can change position, speed, or

direction unless a force acts on it. A book doesn’t just fall off of a table by

itself. A force has to push it! Think about this how do you get your

backpack on your back? You have to lift it and pull it onto your

shoulder. Without a force, your backpack can’t move!!

Measuring Forces

Forces are measured in Newtons (N)

Forces are measured using a spring scale.

Types of Forces

FrictionGravityMagnetic

Friction When a soccer ball is kicked across the

grass, it eventually slows down. Why?

•Friction is a force that works against motion• Friction can make things slow down or stop, or it can keep things from moving at all.

Erasable Friction When you use an eraser, you are

creating friction as your eraser touches the paper.

More About Friction

Friction is greater between rough surfaces than between smooth ones.

Ice skaters glide along the ice because there is little friction between the blades and the ice.

Heat it Up!

Rub your hands together for a minute. You feel heat!

This is because you are creating friction between your hands.

Friction

If you pour oil onto a wooden surface, its friction would be reduced. This is because it makes the surface slippery.

Let’s Review

Oreo likes to race small toy cars. He wants to race them on a surface that will let the cars go further faster. What kind of surface would you suggest? Why?

Let’s Review

The bike tires felt hot from __________ after the boy skidded.

A. magnetism

B. gravity

C. friction

Mr. Gates mops the gymnasium floor every day. When he finishes mopping, he puts up the sign shown below. The effect of which force is weakened when the floor is wet?

A. friction

B. gravitation

C. inertia

D. magnetism

Let’s Review

A puck slides along an icy surface. What makes it slow down?

A. It runs out of push

B. It rubs against the ice

C. It runs out of electricity

Let’s Review

A boy sits halfway down a grassy slope. What keeps him from sliding?

A. Weight

B. Gravity

C. Friction

Let’s Review

Which of the following is an example of trying to increase the friction?

A. Squirting oil in hinges

B. Spreading grit on icy roads

C. Waxing the underneath of skis

Let’s Review

On which surface will a toy car travel the farthest?

A. Ice

B. Wood

C. Carpet

Let’s Review

Which of the following is NOT true?

A. Friction can only slow things down

B. Friction is never useful

C. Friction can stop things from moving