Lecture Four Flashcards
Kepler’s first law
The orbit of each planet around the Sun is an ellipse with the Sun at one focus
What is an eclipse?
Elongated circle with two foci
Kepler’ second law
As a planet moves around its orbit, it sweeps out equal areas in equal times. This means that a planet travels faster when it is nearer to the Sun and slower when it is farther from the Sun.
What is the perihelion and aphelion?
Perihelion - close to Sun
Aphelion - away from sun
Kepler’s third law
More distant planets orbit the Sun at slower average speeds, obeying the relationship
Kepler’s third equation
p2 = a3
History of ideas on how objects move. Three key thinkers.
History of ideas rests on three key thinkers:
Galileo: first Theory of Relativity
Newton: Laws of Motion
Einstein: Special Theory of Relativity & General Theory of Relativity
Galileo’s theory of relativity
- Free motion is constant in speed and direction
- A freely falling body is constantly accelerated
- A body sliding without friction down an inclined plane experiences a constant acceleration gsinθ
- It is not possible to tell if a ‘vehicle’ is in constant motion
Why is there no such thing as an observer at rest?
F
Types of motion
- Speed: rate at which an object moves
speed = distance time units of m/s - Velocity: a speed in a particular direction
- Acceleration: any change in velocity
Acceleration due to gravity
All objects fall at the same rate. On earth g is about 10m/s, meaning speed increase 10m/s every s
Momentum equation
Mass X velocity
Mass v weight
Mass - amount of stuff in a regs body
Weight - the net force acting on a body (usually gravitational)
