Transcript Gravity - TeacherWeb

Gravity
8th Grade
Investigation 7
Force and Motion
Gravity
• Gravity: a force pulling masses toward
each other.
– On Earth, the gravitational force is the
force of attraction between Earth (one of
the masses) and another object.
Gravity
• The strength of the gravitational force
depends on the size of the masses.
– Larger objects pull with more force than do
smaller masses.
Free Fall
• Gravity is the force that makes things
fall toward Earth.
– Because the force applied all of the time,
any object that is not retarded by another
force will accelerate toward Earth = Free
Fall.
Acceleration Due to
Gravity
• All objects fall with the same
acceleration when they are in free fall
(9.8 m/s2).
– Objects like cotton balls & feathers don’t
fall as fast as rocks and shoes because
they are slowed by air resistance.
Air Resistance
• Air resistance is like friction, it acts to resist
motion.
• The force of air resistance acts in the
direction opposite to the force of gravity.
– The net force pulling the cotton ball toward Earth
is less than the force of gravity, so it takes longer
to fall than an object in free fall.
Free-Fall
• The force of gravity makes heavy and
light objects free-fall at the same
acceleration.
– Galileo discovered that objects of different
masses fall together, hitting the ground at
the same time.
– Example: Foil ball vs. paper ball.
Force of Gravity
• The force of gravity accelerates objects
in free fall and objects rolling down hill.
• Gravity is a universal force of attraction
between masses.
Acceleration Due to
Gravity
• Example: Speedometer - measures
speed.
– If a boulder dropped from a cliff, it would
fall 10 m/s faster than it was in the
previous second due to gravity.
Acceleration Due to
Gravity
• The change of velocity in the boulder
example is the acceleration due to
gravity.
• The velocity of an object during its fall
can be calculated by the velocity
equation: v = a x t