Module 2 Notes
Kepler published his three laws of planetary motion in the early 1600s:
a) Kepler’s First Law: The orbit of each planet around the Sun is an ellipse with the Sun at one focus
Eccentricity was established whereby a circle has an eccentricity of zero and a straight line has an
eccentricity of 1; this is useful in determining the ellipses of orbits
b) Kepler’s Second Law: As a planet moves around in its orbit, it sweeps out equal areas in equal times
When a planet is closer to the Sun (around its perihelion) it moves faster along its orbit than when close
to the aphelion (further point from the Sun). The planet moves from A to B (perihelion) in the same
time that it takes to go from A’ to B’ (perihelion).
c) Kepler’s Third Law: The squares of the periods of any two planets have the same ratio as the cubes
of their semi-major axes
2 3
p = a where p is the orbital period in years, and a is the avg. distance from the Sun in AU
Galileo introduced the telescope to the world in the early 1600s and proved the Earth was not the
centre of the universe and in fact the Sun-centred model was correct.
Newton’s Universal Law of Gravitation: if the mass of either object is doubled, the force doubles
- also, if the distance between the masses doubles, the force diminishes by a factor of 4 (two squared)
Tides are a good example of this, and they are caused by the difference in gravitational attraction from
one side of the Earth to the other.
When the Sun, Moon and Earth are all lined up, the tides are highest and called spring tides.
During first and third quarter Moons, the tides are called neap tides The Scientific Method
a) Deductive reasoning – process of concluding that something is true because it is a special case of a
general principle that is known to be true
- logically valid and this is the fundamental method in which mathematical facts are shown to be true
b) Inductive reasoning – process of reasoning that a general principle is true because the special cases
you’ve seen are true; for example, if all the people you’ve met from a particular town have been
intelligent, you might say that “all the residents of this town are smart”
Any model, hypothesis or theory can never be “proved” – a theory always remains a theory until some
observation discredits it.
Pseudoscience – false science; ex. making predictions based on tarot cards, psychic determinations
Nonscience – predictions based on intuition, faith, political conviction and tradition
Cosmological Principal
- there is nothing special or unique about Earth; our location in the Universe is by chance
- the laws of physics and chemistry are valid throughout the universe
Orbital Motion
1. An object orbiting Earth, and any orbiting object, is actually falling (being accelerated due to the
gravitational force) toward Earth’s center
2. Objects orbiting each other actually revolve around their mutual center of mass
3. If you want to leave Earth and never return, you must give your spaceship a high enough velocity so it
will follow an open orbit
Momentum – the inertia an object has
p = m v whereby p is momentum, m is mass and v is velocity
Properties of a Wave
- wavelength – the length of one wave (λ)
- frequency – the number of waves passing a point in space per second (f)
- speed – how fast the wave moves through space (c)

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