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GRAVITY
Chapter 9.2
Assignment #11
What is Gravity?
• GRAVITY
• A force of attraction
between objects that
is due to their masses
– All matter has mass
SO all matter is
affected by gravity
– Universal force
Gravity and the Earth
• Earth’s gravitational
force
• Large mass
– Large gravitational
force
– Everything is pulled
toward the center of
Earth
Mass vs. Weight
• MASS
• Amount of matter in an
object
– Does not change
– Unit = kilogram (kg)
• WEIGHT
• Measure of the
gravitational force on an
object
– Changes when
gravitational force changes
– Unit = newton (N)
Mass vs. Weight
Your weight on the moon would be about onesixth of your weight on Earth, but your mass
would be the same.
Weight…FYI
• When you use the bathroom scale, you
are measuring the gravitational force
between your body and Earth…so, you
are measuring your weight, which should
be given in newtons!
Galileo Galilei
• Galileo Galilei
• Proved that the mass
of an object does not
affect how long it
takes for the object to
fall to the ground
Background Information:
Acceleration
• Velocity
• Acceleration
• Tells how fast an
object is moving
(speed) and which
way it is going
(direction of motion)
• Change in velocity
over time
– Change in speed or
direction
Gravity & Acceleration
• Acceleration due to
gravity
• Objects fall to the ground
at the same time because
the acceleration due to
gravity is the same for all
objects
• Acceleration depends on
force and mass
– More mass, more
gravitational force
– BUT more difficult to
accelerate
Gravity, Acceleration, & Velocity
• Acceleration due to
gravity (g)
• Objects accelerate
toward Earth at 9.8
m/s2
• Change in velocity
(∆v) of falling objects
• ∆v = g x t
1) 9.8m/s2 x 2s = 19.6 m/s downward
2) 9.8m/s2 x 4.5s = 44.1 m/s downward
3) 98m/s / 9.8m/s2 = 10 s
4) 14.7m/s / 9.8m/s2 = 1.5 s
Air Resistance
• AIR RESISTANCE
• The force that
opposes the motion of
falling objects
– Depends on size,
shape, and speed of
the object
Terminal Velocity
• TERMINAL
VELOCITY
• The constant velocity
of a falling object
when the force of air
resistance (upward
force) equals the
force of gravity
(downward force)
• Acceleration stops at
terminal velocity
Gravity and Projectile Motion
• PROJECTILE
MOTION
• The curved path that
an object follows
when it is thrown or
launched near the
surface of Earth
– Two parts:
• Horizontal motion
• Vertical motion
– Produced a curved
path when combined
Horizontal vs. Vertical Motion
• Horizontal motion
• Motion parallel to the
ground
• Vertical motion
• Motion perpendicular
to the ground
– Affected by gravity