Newton’s Laws

Solar System Galileo & Copernicus explained: Kepler explained: Planets have elliptical orbits around the Sun Planets orbit at different speeds. Planets cover equal area in equal time. The farther the distance from the Sun, the greater the orbital period. The Sun was in the center of the solar system

Isaac Newton (1642 – 1727) One of the most brilliant theoreticians to ever live. Explained WHY the planets move as they do. He formulated three laws of motion and the law of universal gravitation.

Terms to describe motion FORCE: A push or pull that changes the motion of an object VELOCITY: Describes how fast (speed) an object moves in a direction

Newton’s 1st Law of Inertia: Objects in uniform straight line motion continue in straight line motion unless an outside force is applied to change their motion Once in orbit, a planet will CONTINUE its orbital motion at constant velocity until an outside force (asteroid, another planet?) acts on it to change its orbit.

Gravity Gravity: a FORCE that pulls every mass toward every other mass Since Earth is the largest mass around – gravity pulls everything toward the center of Earth You have mass. Are you gravitationally attracted to the person sitting next to you?

Gravity is Universal

“To every action there is an equal and opposite re-action.” Newton’s Third Law “To every action there is an equal and opposite re-action.” Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first object. Forces are interacting in PAIRS – one object on another Mass #1 Mass #2

Gravity is the way that masses communicate with each other! Every mass in the universe is attracted to every other mass. I’m attracted to you more! I feel your force of attraction 2 kg 1 kg

Gravity is related to Mass The more mass an object, the more gravity!! Which planet has more gravitational pull? VS

“center’ of gravity There are A LOT of particles in an object We say that the force on an object acts as though all the mass was concentrated at the CENTER of the object. Example: d

Law of Universal Gravity Mass attracts mass

Newton’s Law of Gravity Formula? Fg = Gm1x m2 d2 Mass of one object Mass of a second object squared Distance between them

Big “G” is a constant (a multiplier) It’s the ‘amount’ of force of attraction between two bodies each with a mass of 1 kilogram 1 meter 6.67 x 10-11 N*m2/kg2 or .0000000000667

Rotate around the room to find masses and distances for complete the table

Calculate the force of gravity by dividing the masses by the distance2

1 kg 1 kg 2 kg 2 kg

Force of gravitational pull 1 2 4 8 16 64 MASS x MASS kg

Distance and Gravity Does gravity get more, less, stay the same as you go further DISTANCE from earth?

1 kg 1 kg 2 kg 2 kg

Predicted trend for Distance vs. Gravity If distance between objects increases, Then the force of gravity will decrease

11 1/4 (.25)

According to Newton’s Law of Gravity, Can the orbiting space station get away from the Earth’s gravity? Is there such a thing as “zero” g? NO! Then why do the astronauts appear to be floating? What would happen to the space station is it was free from Earth’s gravity?

If the Earth’s gravity force is attracting the moon, Then Why doesn’t the moon get pulled into Earth? The moon has VELOCITY! It’s moving with a constant speed in a direction – straight. As long as the FORCE of gravity toward Earth is EQUAL to the forward motion of velocity of the moon it will ORBIT

PHET on Orbits Bell work The force of gravity (pulls, pushes) masses. The more mass, the ____ gravitational pull. The more distance, the ________ the gravitational pull. What 2 forces keep an object in motion: Diagram what would happen to an orbiting planet if: gravity was turned OFF The planet slowed down in orbit (decreased velocity) The planet increased its speed (velocity)

Gravity Facts Attractive force between all objects with mass Universal – everything with mass has it and is affected by it Mass & gravity = directly proportional m↑, g↑ Distance & gravity = inversely proportional d↑, g↓ Attractive force is from centers of objects NEVER be zero