Lecture 5 G. Bare Bones Physics Study Sheet
0. Galileo: Neglecting air resistance, light & heavy objects of fall at same speed on Earth.
- If lighter objects fall more slowly, Galileo said, then you should be able to
slow down a heavy object by adding a light one to it!
1. Newton's First Law: change in an object's direction or speed means a force
is acting on that object.
- If an object turns, speeds up, slows down, stops, or starts, then a force is acting on
it!
2. Newton's Second Law: more force is required to alter a more massive object's motion the
same amount.
- It requires more force to stop a truck than a bicycle going same speed!
3. Newton's Third Law: forces always come in equal and opposite pairs.
- you're exerting an opposite force on whatever exerts a force on you!
4. Gravity: F = G x M1 x M2 / R2
- Gravity is weaker farther away from attracting mass; also, alter either mass, and
gravity changes by same amount.
5. Angular momentum is conserved.
- Remember figure skaters -- moving arms in makes them rotate faster!
6. Kepler's First: Planets' orbits are ellipses.
7. Kepler's Second: Line from Sun to planet sweeps out equal areas in equal times.
- just like a ball you toss away from Earth, planets are slowest far from Sun, and
fastest near it
8. Kepler's Third: (period)^2 = (distance)^3
- (longer periods = longer distances) or (smaller periods = smaller distances)