Transcript Slide - Fort Lewis College

Charles Hakes
Fort Lewis College
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Chapter 1
Newton
and Gravity
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Fort Lewis College
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Outline
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Notes
Kepler Review
Newton’s laws
Gravity
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Fort Lewis College
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(Lab) notes
• Remove folder debris
• Do Kepler small group lab this week.
• Due Friday at 6:30 P.M.
• In box outside room 671.
• Sunset 2 - you MUST have Sunset 1
completed and returned FIRST
• Due Friday in one week.
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Fort Lewis College
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Review
• Did not get thrown into the abyss: 1
• Other favorite answers…
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The speed of light.
I don’t know - I’m not king!
My Holy hand grenade blew it up
“42”: (mixing your fiction).
I’m from Oklahoma and have no clue
… for a chimney swallow while hunting
mosquitoes….
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Fort Lewis College
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Review
• What was the most important thing
you learned?
• A circle is actually a special kind of ellipse
with only one focal point
• A square is to a rectangle as a circle is to an
ellipse
• The semi-major axis is half of the major axis.
• If the semi-major axis of two bodies is the
same, they take the same amount of time to
orbit.
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Fort Lewis College
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Group Exercise
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Assume a comet has a period of 5.2
years, with eccentricity very close to 1.
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Fort Lewis College
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Group Exercise
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Assume a comet has a period of 5.2
years, with eccentricity very close to 1.
Calculate the semi-major axis.
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Fort Lewis College
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Group Exercise
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Assume a comet has a period of 5.2
years, with eccentricity very close to 1.
Calculate the semi-major axis.
p2 = a 3
What is the major axis?
What is the maximum distance this comet
might ever get from the Sun?
Include copy of work in your folder.
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Fort Lewis College
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Figure 1.20
Isaac Newton (1642-1727)
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Fort Lewis College
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An iron weight and a styrofoam ball are dropped
from the same height at the same time.
Which hits the ground first?
A) The iron weight
B) The styrofoam ball
C) They hit at the same time
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Fort Lewis College
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Newton’s “Laws”
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Fort Lewis College
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Newton’s 1st Law
If there are no external forces on an object,
then:
• If it is at rest, it will stay that way - forever.
• If it is moving, it will keep doing so at constant
velocity, in a straight line - forever.
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Fort Lewis College
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Newton’s 1st Law
• Inertia - the natural tendency of an object
to stay at rest, or remain moving with a
constant velocity.
• Mass is a quantitative measure of inertia.
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Fort Lewis College
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Momentum
• Momentum - the product of mass and
velocity.
momentum = mass x velocity
• A concept related to Inertia
• Momentum (both linear and angular) must be
conserved.
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Fort Lewis College
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Which object has the most momentum?
A) A cruise missile
B) A ship
C) A glacier
D) Need more information
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Fort Lewis College
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Which object has the most momentum?
A - A cruise missile
1000 kg
100m/s
B - A ship
10 million kg = 107 kg
10 m/s
C - A glacier
1012 kg
1 m/day (~10-5 m/s)
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Fort Lewis College
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Which object has the most momentum?
A - A cruise missile
B - A ship
C - A glacier
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Fort Lewis College
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Angular momentum demonstration
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Fort Lewis College
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Angular momentum demonstration
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This is why planets move faster
closer to the sun.
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Fort Lewis College
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Newton’s 2nd Law
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The net force on an object is equal to the mass
of the object times the acceleration of the object
F =ma
net
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The SI units of force are newtons (N).
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Fort Lewis College
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Newton’s 2nd Law
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Force - something that is capable of changing
an object’s state of motion (it’s velocity)
Fnet - the sum of all forces on an object
Dynamics - the study of changes in motion and
what causes those changes
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Fort Lewis College
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Newton’s 2nd Law
Fnet = m a
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Fort Lewis College
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Newton’s 3rd Law
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…the one hard to believe…
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Fort Lewis College
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A brick hits a glass window. The brick breaks the glass,
so the magnitude of the force of the brick on the glass is
A: is greater than the magnitude of the force of the glass on the brick
B: is smaller than the magnitude of the force of the glass on the brick
C: is equal to the magnitude of the force of the glass on the brick
D: none of the preceding
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Fort Lewis College
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Newton’s 3rd Law
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For every action (force) there is an equal and
opposite reaction (force).
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Important note - the action-reaction force
pairs do NOT act on the same object.
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Fort Lewis College
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A brick hits a glass window. The brick breaks the glass,
so the magnitude of the force of the brick on the glass is
A: is greater than the magnitude of the force of the glass on the brick
B: is smaller than the magnitude of the force of the glass on the brick
C: is equal to the magnitude of the force of the glass on the brick
D: none of the preceding
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Fort Lewis College
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Gravity
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Fort Lewis College
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Figure 1.22
Gravity
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Fort Lewis College
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Figure 1.24
Sun’s Gravity
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Fort Lewis College
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Gravity
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Any object having Mass will exert a gravitational
force on other massive objects.
Force is proportional to mass of each object
F  M1 M2
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Fort Lewis College
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Gravity
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Any object having Mass will exert a gravitational
force on other massive objects.
Force is proportional to mass of each object
Force decreases with the square of the distance
between the two objects
F  M1 M2 / r2
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Fort Lewis College
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Figure 1.23
Gravitational Force
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Any object having
Mass will exert a gravitational
force on other massive
objects.
F  M1 M2 / r2
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Fort Lewis College
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Gravity
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Any object having Mass will exert a gravitational force on
other massive objects.
Force is proportional to mass of each object
Force decreases with the square of the distance between
the two objects
Proportionality constant is “G”, the universal gravitational
constant
G = 6.67x10-11 (N m2/kg2)
F = G M1 M2 / r2
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Fort Lewis College
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Gravity
F = G M1 M 2 / r 2
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Fort Lewis College
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Newton
• Modification to Kepler’s 1st Law
• Both the Sun and the planet orbit
about the center of mass of the
system.
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Fort Lewis College
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Figure 1.25
Orbits
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Fort Lewis College
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Newton
• Modification to Kepler’s 3rd Law
• That “math” law - updated
P2 (years) = a3 (astronomical units)
Mtotal(solar units)
• For planets around the Sun, this
makes very little difference except for
(even for) Jupiter (0.1% Msun)
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Fort Lewis College
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Which mass pair has the greatest
gravitational force between them?
1: A 5Msolar mass and a 4Msolar mass separated by 4 AU.
2: A 4Msolar mass and a 3Msolar mass separated by 3 AU.
3: A 3Msolar mass and a 2Msolar mass separated by 2 AU.
4: A 2Msolar mass and a 1Msolar mass separated by 1 AU.
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Fort Lewis College
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Which mass pair has the greatest
gravitational force between them?
1: A 5Msolar mass and a 4Msolar mass separated by 4 AU.
2: A 4Msolar mass and a 3Msolar mass separated by 3 AU.
3: A 3Msolar mass and a 2Msolar mass separated by 2 AU.
4: A 2Msolar mass and a 1Msolar mass separated by 1 AU.
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Fort Lewis College
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Group Exercise
Calculate the force between those two masses.
A 2Msolar mass and a 1Msolar mass separated by 1 AU.
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Fort Lewis College
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Three Minute Paper
• Write 1-3 sentences.
• What was the most important thing
you learned today?
• What questions do you still have
about today’s topics?
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Fort Lewis College
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