Transcript Chapter 2, Section 1 Notes

Chapter 2, Section 1 Notes
Gravity and Motion
History
Aristotle was the first to discuss
gravity.
He believed that the amount of
gravity was dependent on an
object’s mass.
Galileo Galilei challenged Aristotle
He argued that mass of an object
does NOT affect the time it takes
that object to fall to the ground.
He tested this by dropping two
cannon balls of different masses
to the ground. They hit at the
same time!
Gravity and
Acceleration
Acceleration is the rate at which
velocity changes over time.
Objects fall to the ground at the
same rate because the
acceleration due to gravity is the
same for all objects.
Acceleration of all object toward
2
Earth= 9.8 m/s
Acceleration depends on force and
mass.
An object with a lot of mass does
have a larger force acting upon it,
but it is harder to accelerate. This
is why objects of different mass
can fall with the same
acceleration
Velocity of
Falling objects
• To calculate the change of velocity of a falling
object, use the following equation
•
V= g x t
•
•
= change
• V= velocity
• g= acceleration due to gravity, 9.8m/s2
• t= time( seconds)
Air Resistance and
Falling Objects
Air resistance is the force that
opposes the motion of objects
through air.
Air resistance is dependent on size,
shape and speed of an object. For
example, air resistance would affect
a flat piece of paper more than a
crumpled pieces of paper.
Increased speed = more air resistance
Air resistance will increase until it
is balanced with the downward
force of gravity.
Once the net force is 0 Newtons,
the object will fall at a constant
velocity known as its terminal
velocity
If there is no air resistance, and
object is said to be in free fall.
Free Fall occurs if the only force
acting on
an object is gravity.
Free fall can only occur where
there is no air, such as in a
vacuum.
Orbiting Objects are
in Free Fall
An object orbits when it travels
around another object in space.
A spacecraft that orbits Earth
moves forward, but is also in free
fall towards Earth, this causes the
spacecraft to orbit.
The 2 forces ( forward + down)
allows the shuttle to follow the
curve of the Earth’s surface, and
allows it to orbit.
The astronauts inside a spacecraft
are also in free fall, which is why
they float.
Other objects also
orbit in space.
( the moon, planets, star, etc)
Objects that orbit are in a constant
circular motion, and are always
changing direction. This is caused by
a constant unbalanced force, known
as centripetal force. This force is
caused by gravity.
Projectile Motion
and Gravity
Projectile motion is the curved
path an object follows when it is
thrown or propelled near the
surface of Earth.
There are two components to
projectile motion
• horizontal motion: motion that is
parallel to the ground
• vertical motion: motion that is
perpendicular to the ground(gravity)
Examples of projectile motion:
• frog leaping
• diving into a pool
• shooting an arrow