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Transcript
Gravity
brought to you by: mass and Laura Akesson
scienceoverdrive.org
NASA for Educators
• nasa.gov
For Educators
Find Teaching Materials
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Four Fundamental Forces
Force
Order of
Magnitude
Strong
1040
10000000000000000000000000000000000000000
Electromagnetic
1038
100000000000000000000000000000000000000
Weak
1015
1000000000000000
Gravity
1
100
What causes gravity?
MASS
• Every piece of matter
attracts every other
piece of matter
• The net force of gravity
acts between the center
of masses (can be
estimated to be the
radius of the earth).
Exactly how attractive am I?
NEWTON’S UNIVERSAL LAW OF GRAVITATION
Dude, that guy’s
everywhere…
m1m2
Fg  G 2
r
G is the gravitational constant = 6.67 x 10-11, m1 and m2 are
masses in kg, and r is the distance between their centers
in meters.
Less attractive
more attractive
Take your mass and your neighbor’s mass
in kilograms. Calculate the force of gravity
between you. F  G m m G = 6.67 x 10
1
g
r
2
-11
2
Why are we all not flying towards
eachother?
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On Earth:
All objects fall at the same rate
g = 9.8 m/s2
•
Because an object’s inertial mass is equal to its gravitational mass
• Ignore air resistance
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Galileo’s Gedanken Experiment
 2 men stand side by side. One fires a bullet
horizontally out of a gun at the SAME
MOMENT the other man drops a bullet.
Which bullet hits the ground first?
Mythbusters:
Part 4 (4 min)
Part 5 (6 min)
CODA
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Conservation of Energy
It’s the Law
Energy is neither created nor destroyed.
It is transformed from one form to another.
Etotal = constant
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Mechanical Energy
• Gravitational Potential Energy (GPE)
• Kinetic Energy (KE)
• Elastic Potential Energy
Non-mechanical Energy
• Friction (Heat)
• Light
• Sound
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KE and GPE
Energy of
motion
1 2
KE  mv
2
GPE  mgh
UNITS of energy: Joules (J)
Etotal = constant = 50 000 J
Energy of
position
PhET: Energy Skate Park
http://phet.colorado.edu/en/simulation/energy-skate-park
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APPENDIX
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Inertial vs. Gravitational mass
Fg = mg
Inertial mass
g is the acceleration due to gravity
Gravitational mass
m1m2
Fg  G 2
r
mrock mEarth
mrock g  G
2
rEarth
mEarth
g G 2
rEarth
Since G, mEarth and rEarth are constant, g is constant
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Comparative accelerations due to
gravity around the world
The table below shows the gravitational acceleration in various cities around the world; amongst these cities, it is
lowest in Mexico City (9.779 m/s²) and highest in Oslo and Helsinki (9.819 m/s²).