Forces, Motion, and Newton

8th Grade

Unit 5

Mr. Olsen

CAR CRASH INTRO

“Understanding Car Crashes – it’s basic physics!”

Visualize

Visualize the physical reactions you would experience during a car ride.

Close your eyes and listen to the scenario that Mr. Olsen will tell you. While you are listening, visualize how you might react to the different situations that are presented.

Forces

What is force?

Is it this ------>

Forces

No that’s not it.

Really what is

force?

Force

Force

Do you give up yet???

Do you think Mr. Olsen can use “THE FORCE” to knock over a row of dominoes

Force

Now maybe you can tell me what the definition of a force is.

Domino Demonstration

Force

It is a push or a pull in a certain direction

Force

Now that you know what a force is, what

do forces do?

Forces

2 types of force:Contact

Example: Lifting a book with your hand. Your hand is in CONTACT with the book causing it to move.

Non-Contact The earth pulling down on the book with the force of

gravity. Gravity is a NON-CONTACT force.

Forces

Other Non-Contact forces include:

Electric forces

Magnetic forces

Other Contact forces include:

Friction

Buoyancy

Forces

Every time a force is exerted, the force has:

AGENT (who exerts the force)DIRECTION (in what direction is the push or

pull)RECEIVER (who/what gets pushed or pulled)RESULT (what happened because of the force

being exerted)

Forces

If forces always change the motion of an

object, why might a block of wood

standing upright on a table stay at rest

when the Earth’s gravity is pulling down

on it?

Forces

Forces are measured in Newtons (N)One Newton is a magnitude of force

required to accelerate an object with a mass of one kilogram – one meter per second.

Forces

What are some examples of some forces that can be found on this planet?

Gravity

Gravity is an example of a force that many of you might be familiar with.

What is Gravity?

Gravity is the word we use to describe the pull between masses.

Things with more MASS produce a greater Gravity

pull on each other.

Gravity

Newton’s Law of Gravity:

Every massive particle in the universe

attracts every other massive particle with

a force which is directly proportional to the

product of their masses

A Little Song About Gravity

Click on the music note to

hear the gravity song!

Gravity controls….

A roller coaster’s ride

A diver’s dive

A skier’s jump

A baseball’s fall

What word describes how much of you there is?

Mass

Your mass is the amount of material that your body contains. How can you gain mass?

I’d eat a looott of yummy bread to

gain mass!

Does something that is bigger always have more

mass?

Does bigger = more mass?

So, having more mass does not mean taking up

more space!

Mass vs. Weight

Do things that have more mass always

weigh more?

When you stand on a bathroom scale, the scale is made of springs. The farther down you push the springs, the higher the number on the scale. The number tells you your weight. On earth it is true that the more mass you have, the more weight you have.

Weight? Mass? I am totally confused!

Pretend That You Are in Space!

You are floating around. You drift over to a floating bathroom scale and put your feet on it. Your feet do not push down on the scale at all. The scale shows that you weigh 0. You have lost your weight—but did you lose your mass?

Oh where, oh where, has my weight gone? Oh where, oh where

can it be?

All my body parts are still together—so I still have

mass!

On a space flight, your mass would be the same; but your weight would change.

Summing up Mass and Weight

Your MASS is the amount of material in your body.Your MASS doesn’t depend on where you are.Your WEIGHT is how much your body pushes down on a scale.Your WEIGHT depends on how much MASS you have and where you are.

Where would you weigh the most?

EARTH MARS

Remember, gravity describes the pull between masses. You have mass, and the earth has mass. There is a pull between you and the earth. We measure this pull with a scale. The more the gravity, the greater the squeeze on the springs of the scale…and the more you weigh.

Gravity and Weight Summary

Your weight on earth is a measure of the GRAVITY pull between you and the earth. Bodies with more MASS produce a greater GRAVITY pull on each other.

On Earth

So, if I ate a lot of yummy tuna fish

while standing on the scale, I would gain

mass.

The pull between the earth and me would

become greater—and I would weigh more!

MARS

During my trip to MARS, my mass does

not change, but the moon has much less mass than the earth.

Still on MARS!

There is less gravity pull between you and MARS. If you stood

on the scale on MARS—you would weigh less than on

EARTH!

Imagine…..