Ch 4
Section 2
Gravity
Gravity
!  The gravity between two objects depends on the
distance between them and their size.
!  Gravity is one of the 4 basic forces in the universe
Law of Universal Gravitation
m1m2
F =G 2
d
F= force
G=gravitational constant 6.67 × 10 −11 m 3 /kg • s 2
m=mass of two objects
d=distance between two objects
€
Gravitational force equation
F = mg
F= force
m=mass
g= acceleration due to gravity (9.8m/s2)
weight
!  Your weight is due to the force that gravity pulls your
mass down towards the center of the earth.
Weight and Mass
!  They are not the same.
!  Your weight can change while your mass can be the
same.
!  Your mass may not change but your weight on the moon
is different than when you’re on earth.
Weightlessness
!  Objects in freefall appear to be without any weight.
!  Think of an astronaut in space floating.
!  Astronauts are actually falling in space and appear to
be floating
Projectile motion
!  When ever something is thrown or shot through the air
it is known as projectile.
!  Gravity exerts an unbalanced force pulling the projectile
down
!  This vertical motion is why a projectile appears to travel
with a curved path.
Centripetal force
!  When an object is traveling in a curved path, the
objects net force is towards the center of the circle it is
traveling in.
!  Earths gravity is what keeps the moon in orbit traveling
in a curved path.