Transcript amanda`sGravity and Free Fall

Gravity and Free Fall
By Amanda Stevens
Physical Science
5th period
How does it work?
Why do objects fall to the ground? What
keeps the planets in motion in the sky?
Law of Universal Gravitation
Sir Isaac Newton realized they were two
parts of these questions.
He generalized his observations on gravity
into a law.
The law states that all objects in the
universe attract each other through
gravitational force.
Universal Gravitational Equation
F=Gm1m2
d2
Gravitational force increases as one or
both masses increase. The gravitational
force decreases as the distance between
the masses increases.
All Matter Is Affected By Gravity
Whether two objects are big or small, there
is gravitational pull on them.
Larger objects (such as the earth) the force
is easy to detect.
Gravitational Force Decreases as
Distance Increases
The force also depends on the distance
between two objects.
If the distance between two balls the same
size is doubled, the gravitational force
decreases to ¼ its original value.
Free Fall
Skydivers are considered to be in free fall
before the parachute opens, but that is not
the case.
Free Fall and Weight
Free fall- the motion of a body when only
the force of gravity is acting on it.
The free-fall acceleration of an object is
directed toward the earth at 9.8m/s/s
Because air resistance is absent, all
objects near earth’s surface fall at the
same rate no matter what their mass is.
A feather and an apple dropped from 3 ft
high, would hit the ground at the same
moment.
Free fall acceleration is constant
Here, three balls, all
weighing different
are being dropped at
the same time. They
will hit the ground
at the same time.
weight equals to mass times freefall acceleration
Weight = mass X free-fall acceleration
w = mg
Astronauts seem to be weightless, but truth
is, nothing can ever be weightless.
Gravitational force is not as strong on the
moon as is on earth, making the
astronauts, making them to seem to “float”
Velocity is constant when air
resistance balances weight
Terminal velocity-the constant velocity of a
falling object when the force of air
resistance is equal in magnitude and
opposite in direction to the force of gravity.
A falling object stops accelerating when the
force of air resistance becomes equal to
the gravitational force.
Free fall and motion
An object is in free fall only if gravity is
pulling it down and no other forces are
acting on it.
Because air resistance is a force free fall
can occur only where there is no air. (a
vacuum or in space)
Objects in space are in free fall because
there is no air. They fall at the same rate of
acceleration, no matter how great or small
their individual masses are.
Orbiting objects are in free fall
Why do astronauts appear to “float” in a
space shuttle? Is it because they are
weightless in space?
The gravitational force will be there, though
almost undetectable in space, because it is
so far away, but nothing can ever be
weightless. You would still have mass.
Astronauts “float” in orbiting spaceships,
not because they are weightless, but
because they are in free fall.
Projectile Motion and Gravity
The orbit of the space shuttle around earth
is an example of projectile motion
Projectile motion- the curved path that an
object follows when thrown, launched, or
otherwise projected near the surface of the
earth; the motion of objects that are moving
in two dimensions under the influence of
gravity.
The downward acceleration due to gravity
does not change a projectile’s horizontal
motion, and that does not affect the
downward motion.
Sources
Yahoo Images