A force is a push or pull on an object.

Forces have both size and direction.

Forces can be balanced or unbalanced.

Based on your prior knowledge, what is friction?

Friction is a force that RESISTS motion. (works against it)

Occurs when two objects are in contact with one another.

What two objects are experiencing friction in these examples?› A person walking› A car driving on the street› A boat sailing on a lake› An airplane flying in the air

Which force represents friction in a car driving down the street?

525 N

1025 N

Change the surface of the objects› Rougher surface=Greater Friction

Increase the force keeping the objects in contact› Ex. Rubbing your hands together

Change the surface of the objects› Smoother surface=Less Friction

Decrease the force keeping the objects in contact› Ex. Rubbing your hands together

Use a lubricant (ex. Oil, grease, water)

Why does a surface covered in ice have less friction than a surface not covered in ice?

Think of some activities that would change if there was no friction.

Based on your prior knowledge and observations, what is gravity?

Gravity is a force that attracts objects to each other.

Every object has its own force of gravity.

Gravity PULLS objects towards the center of the object.

The strength of gravity depends on the objects MASS. › More MASS=More GRAVITY› Most objects are too small to exert a

detectable amount of gravity Gravity increases as you near the

center of the object. What objects gravity do we experience

the most?

The Less MASS an object has the Less GRAVITY it exerts.

The farther away from the objects center, the less gravity exerted by that object.

Why do astronauts experience less gravity on the moon?

Denver is on average a mile above sea level while New Orleans is on average 100ft below sea level. At which city will you experience more gravity from the Earth?