Download of an object

Force Unit
Part 2: Gravity
Objectives




Explain the law of universal gravitation and
how applies to objects on Earth both still and
falling and in space.
Explain how free-fall acceleration and terminal
velocity are connected.
Describe the difference between mass and
weight and their connection to gravity.
Explain how projectile motion works and how
we use it to our advantage in sports and in
space
Questions


Have you ever seen a
videotape of the first
astronauts on the moon?
Why did the astronauts-who were wearing heavy
spacesuits—bounce so
easily on the moon?
Law of Universal Gravitation
Established by Sir Isaac Newton
 It states that all objects in the universe
are attracted to each other through
gravitational force
 Mathematically it is defined as:
F = G m1m2
d2
G = _______________________
d = _________________________________

Fundamentals of Gravity



All matter is
affected by
gravity
Gravitational
force increases as
mass _________
Gravitational
force decreases
as distance
____________
Free Fall Acceleration




Happens when ________ is the only
force acting on an object
The free-fall acceleration of an object
is directed toward the center of Earth
It is abbreviated as g and equals
___________
Near the Earth’s surface it is constant
when neglecting air resistance
Weight




It is the amount of gravitational force
acting on the ________ of an object
It is equal to mass times free-fall
acceleration
SI unit is the _____________
Weight also influences shape
The Velocity
Connection


Velocity is a constant
when air resistance
balances weight
During free-fall, an
object stops
accelerating and
reaches its maximum
velocity, which we call
_______________
Free Fall and Motion




An object is only in free fall if gravity
is the only force acting on the object
Air resistance is a force on falling
objects
Free fall can only happen where there
is no ___, such as in a vacuum or space
Orbiting objects, such as moons and
planets, are in free fall
Questions

Do sky-drivers experience free fall
acceleration? Why or why not?

Are you weightless in space? Explain.

Why do astronauts “float” in space?
Projectile Motion


Projectile motion is a curved path that
an object follows when thrown,
launched or otherwise projected near
the surface of the Earth
The orbit of a space shuttle around
Earth is an example of projectile
motion
Projectile Motion Continued



Has two components:
_____________________________
These two components are independent
of each other and thus have no effect
on one another
The two components together form the
curved path of motion for the object
Questions


Because objects in projectile motion
accelerate downward, where should I
aim when throwing a football at my
teammate?
If I want to hit a bulls-eye , where
should I aim the arrow? Why?
True or False Quiz
1.
Disregarding air resistance, free-fall
acceleration near Earth’s surface depends on
mass.
2.
The mass of an astronaut on the moon is the
same as it is on Earth.
3.
Terminal velocity is reached when the forces
on a skydiver become balanced.