Please form up into
groups of 2-4 as soon
as you get into class!
EXAM 1 REVIEW
FORMAT
Key topics will be briefly discussed.
Review questions will be posted. Each
group will have a few minutes to discuss
the question.
One group will be chosen at random to
address the question for the class
OVERVIEW OF KEY TOPICS
What is science?
SI Units: tools for measuring our universe
Models of our solar system
Kepler’s Laws
Newton and Motion
Gravity
Current Exploration of Our Solar System
WHAT IS SCIENCE?
Scientific Theories must
be falsifiable.
The only acceptable
authorities in science are
experiments and
observations.
Science attempts to
explain patterns found in
nature.
REVIEW QUESTION 1
Give an example of a non-scientific
theory and explain why it is not
science.
UNITS: SI and the Metric
System
SI – System Internationale
Mass – kilogram (kg)
[thought question: what is mass?]
Distance – meter (m)
Time – second (s)
Temperature – Kelvin (K)
Many quantities are measured as a combination
of these units.
Example: acceleration is measured in m/s2
METRIC SYSTEM
pico 10-12 : picometer , picogram, picosecond
nano 10-9 : nanometer
micro 10-6 : micrometer
milli 10-3 : millimeter
centi 10-2 : centimeter
deci 10-1 : decimeter
deca 10+1 : decameter
kilo 10+3 : kilometer
mega 10+6 : megameter
giga 10+9 : gigameter
terra 10+12 : terrameter
REVIEW QUESTION 2
Astronaut Neil Armstrong felt a gravitational
acceleration of 1.6 x 10-9 km (ms)-2
(kilometers per square millisecond) when he
walked on the moon. Convert this value to SI
units.
ANSWER:
1 kilometer = 1000 meters
1 second = 1000 milliseconds
(so 1 s2 = 10002 ms2)
Thus 1.6 x 10-9 km (ms)-2 = 1.6 m s-2
MODELS OF OUR UNIVERSE
Know these names and what they contributed to
science and/or their theories on the nature of our
universe:
Plato
Anaxogoras
Aristotle
Eratosthenes
Ptolemy
Copernicus
Tycho Brahe
Johannes Kepler
Galileo Galilei
Sir Isaac Newton
It will also be helpful to know what observations
they used to support their theories
REVIEW QUESTION 3
Name 3 observations that led Galileo to support
the Copernican model of the solar system.
ANSWER:
1. Phases of Venus - Difficult to explain with the
Ptolemaic model
2. Craters on the moon - the celestial bodies are
not the perfect spheres proposed by Aristotle
3. The moons of Jupiter – the Jupiter system
appeared to Galileo as a mini-solar system; all
the smaller bodies orbiting the largest body
KEPLER’S LAWS
1.
Planets move about the Sun in elliptical
orbits with the Sun at one focus.
2. The line joining a planet to the Sun
sweeps over equal areas in equal
intervals of time.
3. The square of the time of one revolution
of a planet about the Sun is proportional
to the cube of the orbit’s semi-major axis.
REVIEW QUESTION 4
Neptune has an orbital period of approximately
165 years. What is its semi-major axis?
ANSWER:
From Kepler’s Laws:
P2 = (1yr2/AU3) *a3
a3 = P2/1
= (165 yrs)2 = 27225 AU3
a = (27225AU3)1/3 = 30 AU
NEWTON’S LAWS OF MOTION
1. An object remains at rest or in constant
velocity unless acted on by a force.
2. Force equals mass times acceleration
(F=ma).
3. Each action has an equal and opposite
reaction.
GRAVITY
All bodies with mass exert a gravitational
force on each other.
The force of gravity depends directly on
the product of their masses, i.e. bigger
masses, bigger force.
The force of gravity gets weaker the
farther two bodies get from each other.
REVIEW QUESTION 5
Which of these planets experiences the smallest
solar gravity:
Mercury
Jupiter
Uranus
Earth
Answer:
Uranus. Distance is the most important
factor in determining the effects of gravity in a
single solar system. Since Uranus has the
longes semi-major axis, that planet experiences
the smallest solar gravity
GRAVITY CONTINUED
The force of gravity between two objects of
masses M and m at a distance r can be
determined by:
F = G M m / r2
Acceleration due to gravity experience by mass
m can be found from this law of gravity and F =
ma:
ma = GMm/r2
a = GM/r2
ADDING KEPLER’S LAWS
From Newton, we can know fully determine
Kepler’s third law for any solar system:
3
r
=
2
(GM/4π )
2
P
REVIEW QUESTION 6
If planet Angel orbits star Buffy with a semimajor axis of 6 AU and Buffy is 3 times as
massive as the Sun, what is Angel’s
period?
ANSWER:
P2 = 4π2r3/GM
P2 = 4π2(63)/ G(3M☼)
P2 = (4π2/GM☼)*(63/3)
P2 = 72 years2
P ~ 8.5 years
MORE GRAVITY TOPICS
Be sure to be able to answer these question:
What is the difference between mass
and weight?
What is escape velocity?
How do we calculate escape velocity?
CURRENT EXPLORATION
Three spacecrafts were discussed in class.
Be able to briefly describe these missions
and their goals:
Phoenix Mars Lander
Messenger
Lunar Reconnaissance Orbiter
REVIEW QUESTION 7
Which mission discussed in class is the first
spacecraft to orbit the body it is
investigating?
ANSWER:
The LRO will be mapping the Moon,
and the Phoenix mission will land on Mars.
Of the three only Messenger orbits a body
that has not previously been orbited,
Mercury.
GOOD LUCK!
Be sure to come to office hours after class
for further clarification
A practice exam will be posted this
afternoon for even more review questions!