Friction Gravity Forces Review A force is a

Friction & Gravity

Forces Review �A force is a push or pull on an object. �Forces have both size and direction. �Forces can be balanced or unbalanced.

Friction �Based on your prior knowledge, what is friction?

Friction �Friction is a force that RESISTS motion. (works against it) �Occurs when two objects are in contact with one another.

Examples �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

Examples cont. . . � Which force represents friction in a car driving down the street? 525 N 1025 N

Increasing Friction � Change the surface of the objects › Rougher surface=Greater Friction � Increase the force keeping the objects in contact › Ex. Rubbing your hands together

Decreasing Friction � 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)

Friction �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.

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

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.

Increasing Gravity � 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?

Decreasing Gravity � 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.

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