# G RAVITY AND M OTION *** What keeps the Earth and the Moon in Orbit? *** *** Why don’t they just fly off into space? ***

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G RAVITY AND M OTION *** What keeps the Earth and the Moon in Orbit? *** *** Why don’t they just fly off into space? ***

S IR I SAAC N EWTON First person to answer questions about gravity and motion. Discovered his theories in 1666 He realized there must be a force acting between the Earth and the moon and the Earth and the Sun.

GRAVITY Gravity  attracts all objects toward each other He didn’t invent or come up with gravity but he was the first person to realize it happens everywhere. Law of Universal Gravity  every object in the universe attracts every other object The strength of gravity between two objects depends on: The mass of the objects Distance between them

P ENNY EXPERIMENT

DISCOVER ZONE-GRAVITY Get into lab partner groups and then listen for directions You will need: A ruler, stack of pennies, a sheet of paper Procedure Place the stack of pennies on the table Write down a prediction if you were to swipe the bottom penny out Quickly slide a ruler along the surface of the table. Observe what happens to the stack Repeat several times, knocking more pennies from the bottom of the stack.

Why don’t we notice a pull between you and the book? Or you and the ball? Or you and the ground? The strength of gravity depends in part on the masses of each of the objects.

G RAVITY Mass is the amount of matter in an object The more mass an object has the more gravitational pull Weight is the force of gravity on an object This can change depending on place Distance between two objects. When the objects are close together the gravitational pull is stronger When the objects are farther apart the gravitational pull is less Mass and WeightDistance

5 lbs 20 lbs. 5lbs Regular Large small

M OVIE CLIP Look into the basics of gravity with a movie clip from discovery education: http://player.discoveryeducation.com/index.cfm?g uidAssetId=B8FD0AAA-0355-4617-ACD9- B7C08EC61262&blnFromSearch=1&productcode =US

I NERTIA AND O RBITAL M OTION Inertia  The tendency of an object to resist a change in motion. In the car, a seat belt An object with greater inertia is harder to stop Newton’s first law of motion  an object at rest will stay at rest and an object in motion will stay in motion with a constant speed and direction unless acted on by a force. Demonstration with a marble

W HY DO THE E ARTH AND THE MOON REMAIN IN THEIR ORBITS WITHOUT RUNNING INTO EACH OTHER ? View diagram to see how gravity and inertia are combine to keep the moon orbiting around the Earth.

A SSESSMENTS THINK, PAIR, SHARE 1. WHAT IS THE LAW OF UNIVERSAL GRAVITATION? 2. WHAT TWO FACTORS DETERMINE THE FORCE OF GRAVITY BETWEEN TWO OBJECTS?

3. SUPPOSE THE MOON WERE CLOSER TO EARTH. HOW WOULD THE FORCE OF GRAVITY BETWEEN EARTH AND THE MOON BE DIFFERENT? 4. WHAT TWO FACTORS ACT TOGETHER TO KEEP EARTH IN ORBIT AROUND THE SUN?

5. WHY DOESN’T EARTH SIMPLY FALL INTO THE SUN? 6. HOW WOULD EARTH MOVE IF THE SUN (INCLUDING IT’S GRAVITY) SUDDENLY DISAPPEARED? EXPLAIN.

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