Transcript Universal Gravitation

Universal Gravitation
Newton’s Law of Universal Gravitation
states that gravity is universal and that all
objects attract each other with some force
of gravitational attraction
You and the person next
to you are attracted to
each other with some
small force…maybe
around 2 x 10-7 Newtons
The formula for Universal Gravitation is:
F = Gm1m2/d2
G is the gravitational constant (it always
equals 6.67 x 10-11)
○ m1 is the mass of one object
○ m2 is the mass of the other object
○ d is the distance between the two objects
○
How changing the
mass effects the
gravitational force
In general, the
larger the
mass the
larger the force
!
How changing the
distance effects the
gravitational force
Example
Determine the force of gravitational
attraction between Earth, which has a
mass of 5.98 x 1024 kg, and a 70 kg
physics student who is standing at sea
level, a distance of 6.38 x 106 m from
Earth’s center.
F = Gm1m2/d2
F = (6.67 x 10-11)(5.98 x 1024)(70)
(6.38 x 106)2
F = 2.79 x 1016
4.07 x 1013
F = 685 N
Kepler’s Laws of Planetary Orbit
In the 1600’s Kepler came
up with the Laws of
Planetary Motion that are
still used today
These laws go against
what the church at the
time believed (in a Earth
centered solar system)
1st Law: Law of Ellipses
The path of the planets around the sun are
elliptical in shape with the center of the
sun being located at one focus
2nd Law: Law of Equal Areas
This law states that an imaginary line from
the sun to a planet sweeps out equal
areas in equal time intervals
3rd Law: Law of Periods
This law states that the square of the orbital
period (how long it takes the planet to orbit the
sun) is proportional to the cube of its distance
from the Sun
2
P
3
R
Basically, this means the farther
away a planet is from the Sun,
the longer it takes to orbit the
Sun and the relationships are
proportional!