Post on 20-Dec-2015
Review: Kepler's Laws
1. Planets travel aound the sun in elliptical orbits with the sun at one focus of the ellipse.
2. A line connecting the Sun and a planet sweeps out equal areas in equal times.
3. The square of a planet's orbital period is proportional to the cube of its semi-major axis. (P2 α a3)
Review: Newton's Laws of Motion
1. Every object continues in a state of rest or a state of uniform motion in a straight line unless acted on by a force. (Inertia)
2. F = m*a
3. For every action there is an equal and opposite reaction.
Newton's Law of Gravity: F =G m
1
m2
R2
Orbit of Earth around Sun
Gravity and Orbits
• Throwing an object fast enough will put the object into orbit! (Neglecting air resistance)
• Moon is continually “falling” towards the Earth in its orbit (Gravity vs. inertia)
Correction to Kepler’s Third Law
Earth and sun actually rotate about their common center of mass
Corresponds to a point inside sun
Used to detect extrasolar planets
Question
The force of gravity between two objects decreases rapidly with the:
A) product of the two masses.
B) elipticity of the orbit.
C) separation distance.
D) orbital velocity.
Question
The acceleration experienced by a falling object due to Earth's gravity _____ the mass of the object.
A) increases with
B) decreases with
C) is independent of
That one was complicated, because we need to remember:
Fg = G m m
E
R2
AND
a =
Fg
m
So, a =G m m
E
m R2 =
G mE
R2
Chapter 2: EM Waves
What is a wave?
What are the main properties of waves?
What two things do all waves transport?
Waves are a type of disturbance that can propagate or travel.Waves carry information and energy.
Properties of a wave
wavelength ()
crest
amplitude (A)
velocity (v)trough
is a distance, so its units are m, cm, or mm, etc.
Period (T): time between crest (or trough) passages
Frequency (f): rate of passage of crests (or troughs), f
v = f
1T(units: Hertz or cycles/sec)
Equilibrium position
Waves bend when they pass through material of different densities.
swimming pool
air
water
prism
airairglass
Refraction
All radiation (including visible light) travels as Electromagnetic waves.
That is, waves of electric and magnetic fields travelling together.
What are some examples of objects with magnetic fields:
What are some examples of objects with electric fields:
All radiation (including visible light) travels as Electromagnetic waves.
That is, waves of electric and magnetic fields travelling together.
What are some examples of objects with magnetic fields:
a bar magnetthe Earththe Sun
What are some examples of objects with electric fields:
} "charged" particles that make up atoms.
Anything with too many or to few electrons!
Electrical appliancesLightningProtonselectrons
Electric Force - opposites attract, likes repelOscillating charges radiateAll objects have temperatures greater than absolute zero - random thermal motionAll objects radiate!Why don’t we see the radiation coming from many ordinary objects?
Dog whistle analogy
Electromagnetic Radiation
(How we get information about the cosmos)
What are some examples of electromagnetic radiation and what are the different ways in which we might experience them or make use of them?
Electromagnetic Radiation
(How we get information about the cosmos)
What are some examples of electromagnetic radiation and what are the different ways in which we might experience them or make use of them?
Light (see)Infrared (heat)Ultraviolet (sunburn)Microwaves (cooking, communication)AM radio (communication)FM radio (communication)TV signals (communication)Cell phone signals(communication)X-rays (medical applications)