EXPECTATIONS: Determine where gravity exists and what factors affect the force of gravity. Learn the difference between weight and mass. Calculate weight. Describe centripetal force and apply it to Earth’s satellites.

GRAVITY 1. Gravity - the force of attraction between two objects due to their mass. 2. Objects fall to earth because of the pull of earth’s gravity. Galileo found all objects fall towards the Earth with the same acceleration. 3. An object’s acceleration near the surface of the earth is 9.8m/sec/sec.

4. The acceleration due to gravity of an object in real life is effected by air resistance. -If there was no air, which would hit the ground first: a feather or an elephant?

Notice the large and small rocks both have the same acceleration!

-If you add air resistance, which would hit the ground first: a feather or an elephant? http://www.physicsclassroom.com/mmedia/newtlaws/efar.cfm

Notice the ball is accelerating as it goes down.

5. Weight and mass are not the same thing. Mass = a measure of the quantity of matter in an object. Weight= mass X acceleration due to gravity (9.8 m/sec/sec) *Notice that weight is just the unbalanced force from Newton’s 2nd Law (F = m X a)

Find your weight on other worlds! http://www.exploratorium.edu/ronh/weight/

6. Newton determined the Universal Law of Gravitation. a. Every object attracts every other object. b.The force of gravity is directly proportional to the product (multiplied) of the objects masses. This means the larger the object(s), the more gravitational force. c. The force of gravity is inversely proportional to the square of the distance between the two objects. This means, the larger the distance between the two objects, the less the gravitational force.

7. The Law of Universal Gravitation formula.

8. Earth – Moon Interactions The Earth’s gravitational pull on the moon is always pulling the moon towards the Earth. Why doesn’t it ever collide? Newton reasoned that if the cannon projected the cannon ball with exactly the right velocity, the projectile would travel completely around the Earth, always falling in the gravitational field but never reaching the Earth, which is curving away at the same rate that the projectile falls. b. The moon is a just the right distance and velocity that it is constantly in orbit.

Centripetal force is a center- directed force that continuously changes the direction of an object to make it move in a circle. When you spin a bucket of water over your head without spilling a drop, you are also applying a centripetal force. If you let go of the bucket, it will move in a straight line.

What is exerting the centripetal force in these examples?

What is providing the centripetal force here?

http://www. teachersdomain. org/resource/ess05. sci. ess. eiu http://www.teachersdomain.org/resource/ess05.sci.ess.eiu.moonorbit/ Video explaining why the moon does fall into the Earth.