“If I have seen farther than other men, it is because I stood on the shoulders of giants” -Isaac newton CHAPTER 5

5-1 Galileo and newton Kepler discovered the 3 laws of planetary motion, but he did not understand WHY the planets move along their orbit. (Make sure you review and know all 3 laws for the chapter 4 and 5 test!!) He thought that maybe it was a magnetic force or angels pushing the planets along.

5-1 Galileo and newton Newton was born in England- the year Galileo died He refined Kepler’s model of planetary motion, but did not perfect it Newton discovered gravity (the concept of), but did not understand what gravity was.

5-1 Galileo and newton Aristotle- 4 elements Earth, Water, Air and Fire Believed objects fall downward because they are moving toward their proper place. Called these motions natural motions vs violent motions, push and object and make it move other than its proper place.

5-1 Galileo and newton Galileo- before building his first telescope he studied motion and conducted his own experiments. Dropping objects- he found the velocities were so great and the time it took the object to drop was short, it was difficult to measure accurately. rolling balls down a gently sloping incline- found bodies do not fall at constant rates, but are accelerated Objects move faster with each passing second (9.8m/s)= Acceleration of gravity

5-1 Galileo and newton Apollo 15 astronaut David Scott

5-1 Galileo and newton Galileo – noticed that object going down an incline accelerated, while objects going up an incline decelerated “any velocity once imparted to a moving body will be rigidly maintained as long as the external causes of acceleration are removed”- law of inertia

Newton’s 3 laws of motion 5-1 Galileo and newton Newton’s 3 laws of motion 1) a body continues at rest or in uniform motion in a straight line unless acted upon by some force Astronauts drifting in space will travel at constant rates in straight lines forever if no forces act on them Objects continue to move because they have momentum (a measure of its amount of motion) = velocity x mass

5-1 Galileo and newton Newton’s 3 laws of motion 2) The acceleration of a body is inversely proportional to its mass, directly proportional to the force, and in the same direction as the force F=ma F= force m= mass (measure of the amount of matter) a= acceleration (change in velocity) Velocity= directed rate of motion (speed with direction)

Newton’s 3 laws of motion 5-1 Galileo and newton Newton’s 3 laws of motion 3) To every action, there is an equal and opposite reaction Forces must occur in pairs directed in opposite directions.

5-1 Galileo and newton Newton wondered if the force that holds the moon in its orbit could be the same force that causes apples to fall --- gravity Inverse square law- strength would decrease as the square of the distance increased (gravitation pull is weaker the farther away the object is)

5-1 Galileo and newton If Earth pulls on the moon then the moon must pull on Earth. (mutual gravitation) F= - GMm r2 G= gravitation constant R= distance between the masses M= mass of object 1 m= mass of object 2

5-2 Orbital motion and tides How gravity pulls on an object 1) An object orbiting Earth is actually falling towards Earth’s center- misses Earth because of its orbital velocity 2) objects orbiting each other actually revolve around their center of mass 3) closed orbits vs open orbits- need enough velocity to follow an open orbit

5-2 Orbital motion and tides Circular Velocity- lateral velocity the object must have to remain in circular orbit Earth’s gravity extends to infinity Escape velocity- velocity required to escape from the surface of an astronomical body The escape velocity from Earth is about 25,000 miles/hr

5-2 Orbital motion and tides Affected by how gravity pulls on different parts of an object Tides are caused by small differences in gravitational forces

5-2 Orbital motion and tides The side of Earth facing the moon is about 4000 miles closer to the moon than is the center of Earth Moons gravitation pull is slightly stronger when it acts on the near side vs the center This creates a bulge on the near side

5-2 Orbital motion and tides The ocean tides are caused by the accelerations Earth and the oceans feel as they move around that center of mass As Earth turns it carries you into a tidal bulge, the water deepens as it moves away from the bulge, the water becomes shallow Bulges are on opposite sides of the Earth The tides rise and fall twice a day

5-2 Orbital motion and tides Spring tides- occur 2 x a month during a new and full moon- strong pulls Neap tides- weaker pulls

5-3 Einstein and relativity notebook page 52 Special relativity First postulate: definition Ex: Second postulate: The General Theory of Relativity General theory of relativity Equivalence principle Gravity according to general relativity