STUDY GUIDE #2 FOR ASTRONOMY 100,
Schneider & Arny,
Dr. Hedin
Units 1725 and Units 3234
1.
Know the definition of “escape velocity” (in words), and generally how the
mass and radius of a planet affect the escape velocity from that planet.
Escape velocity is the minimum velocity needed to escape a gravitational
field.
i
n physics,
escape velocity
is the speed at which the kinetic energy plus the
gravitational potential energy of an object is zero.
Imagine that a spaceship of mass
m
is at a distance
r
from the center of mass of the planet, whose mass is
M
. Its initial
speed is equal to its escape velocity,
v
e
. At its final state, it will be an infinite distance
away from the planet, and its speed will be negligibly small and assumed to be 0.
Kinetic energy
K
and gravitational potential energy
U
g
are the only types of energy
that we will deal with, so by the conservation of '
energy'
,
The escape velocity is
proportional to the square root of the mass divided by the radius.
The smaller the
radius the higher the escape velocity.
Light is 300,000 km./second.
2.
Know that visible light, radio waves, xrays, etc. are all part of the
electromagnetic spectrum, and know how they compare in wavelength or
frequency.
How do frequency and wavelength and the energy of the
photon relate?
(For example, blue light has higher frequency and energy,
and a shorter wavelength than red light.)
wavelength is difference
between peaks..
(lamda)
frequency is the number of cycles/second that
pass by a given point.
V= lamda * frequency.
A photon is a particle of
light.
Energy= H (constant) * Frequency
higher frequency means higher
energy.
Radio is low frequency hi energy.
Gamma rays high frequency
low energy.
No the whole spectrum
3.
Know which types of radiation are blocked by the Earth’s atmosphere
(thankfully
!). visible light and radio waves easily go through our
atmosphere.
The rest of the waves are blocked.
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 Spring '10
 Duncan
 Accounting, Solar System, Energy, Light

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