MassMass is the amount of
“stuff” (matter) in an object.Measured in grams (kg,
mg, cg, etc.)Mass will not change
unless matter is added or taken away.
Weight Weight is the gravitational force
exerted on an object by Earth (or the moon, Jupiter, Sun, etc.)
It is a FORCE so it’s measured in
Newtons (N). Weight can change
depending on where
you are located.
Galileo Galilei 1564-1642
Italian astronomer and physicist
First true “Experimentalist”.
Set forth the basic ideas of Motion.
All objects fall at the same rate.
(heavy or light!)
Quick Review of Newton’s discoveries…
Laws 1st Law – The Law of Inertia 2nd Law – acceleration = Force mass 3rd Law – Forces occur in action-reaction pairs
Acceleration due to gravity, g All objects regardless of their mass are accelerated
equally by gravity Since this acceleration is so important to the motion
of all objects on the surface of the earth it is assigned g = 9.8 m/s2 (or 10 m/s2)
Gravity Continued…
Freefall - An object accelerates as it falls.
Near the earth objects fall at the same rate regardless of their mass.
g = 9.8 m/s2
Gravity continued… Law of Universal
Gravitation
This law states that the force of
Gravity acts between all
objects in the universe.
Newton & Gravity Isaac Newton was the first
to deduce that the force that makes an apple fall is the same force that keeps the moon in its orbit.
But then he asked himself… Does the falling apple exert a
force on the earth? Why doesn’t the moon fall into
the earth?
Gravity . . .
The apple DOES exert a force on the Earth! Does the Earth notice? Why?
The moon IS falling! HUH?!? Satellite Motion!
Newtonian Mountain
The Story of 9.8… From before we know that a 1 kg mass
exerts a force of 9.8 N on the Earth because…
Fweight = mass x gravity
Fw = (1kg)(9.8 m/s2)
Fw = 9.8 N
Where did this “9.8” come from in the first place?
The Story of 9.8…
F = 9.8 N
1 22 2
becomes... object Earth
Earth
m mmmF G F G
d r
Earth
1 kg mass
distance = radius
11 2 22
1 5.97 x 1024 kg6.67 10 /
6.38 x 106 m
kgF N m kg
Acceleration due to Gravity at Different Places on Earth…
g varies slightly due to differences in the distance from the center of the earth (altitude or latitude) North Pole g = 9.832 m/s2
Panama Canal g = 9.782 m/s2
New York City g = 9.803 m/s2
Denver g = 9.796 m/s2
Acceleration due to gravity on Different Planets…
Jupiter 2.54 x gNeptune 1.20 x gSaturn 1.06 x gUranus 0.92 x gEarth 1.00Venus 0.92 x gMercury 0.38 x gMars 0.38 x gPluto uncertainMoon 0.16 x g
These depend on the planet’s mass and radius.
Guess your weight on Mars!
This website will tell you how much you would weigh if you were on any of the other planets.
http://www.exploratorium.edu/ronh/weight/index.html
Newton’s Universal Law of Gravitation
Depends on… Mass of the two attracting objects (m1 & m2)
Directly proportional
Distance between the two objects (d) Inversely proportional
Universal Gravitation Constant (G) G = 6.67 x 10-11 Nm2/kg2
Who are you attracted to??
Maybe not Romantically by
definitely Gravitationally!
Two bodies are attracted to each other due to their mass and the
distance between them.
Why don’t we always feel a gravitational attraction?
In order for a gravitational attraction to be felt the mass of one of the bodies must be very large. The earth is many times more massive than you are. You can sense the Force of Attraction.
Kepler’s First LawAll planets move about the sun in an
elliptical orbit. In an elliptical orbit the distance between the planet and the sun is continuously varying:
What does the earth’s revolution around the sun
cause?The earth is
tilted on its axis 23.5 degrees. to the plane of the earth’s orbit around the sun
APHELION / PERIHELION
“Helios” - Greek word for sun
Prefix “Ap” - means farthest
Prefix “Peri” - means closest
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