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2.3
• Define:
• Free Fall-the acceleration of
a falling object under the sole
influence of Earth’s
gravitational force.
• Example: Ball thrown upward
after the point at which it
leaves your hand.
• What is not an example of free
fall? Birds, helicopters,
airplanes
• Objects in free fall on Earth
accelerate downward at 9.8
2
m/sec . This is called the
acceleration due to gravity.
The letter g is used to
represent its value.
• To calculate an object’s speed,
you multiply the time it falls by
the value of g .
Describe what happens when you throw a ball
upward in terms of acceleration. (At least 3
sentences)
• The ball will decelerate (slow
down) as it moves upward at a
2
rate of 9.8m/sec . It will come to
a stop for an instant. Then the
ball will accelerate (speed up)
downward at a rate of 9.8m/sec2.
• Define.
• Velocity: Speed with
direction.
• Define.
• Weight: force of gravity on
an object.
• The symbol Fg stands for
“force of gravity” and is used
to represent weight.
Why can’t we use the terms weight
and mass interchangeably?
• Weight deals with the pull of
gravity on an object. Mass simply
deals with how much matter
something has.
• Weight is a force measured in
Newtons or pounds.
• Define.
• Air resistance: The opposing
force on a moving object due
to the resistance of air.
• Example: Feather accelerates at a
rate much less than 9.8m/sec2,
because of the friction of air. The
net force is the weight minus the
force of the air pushing up on the
feather as it falls.
Why does a baseball fall faster than a
feather? (at least 3 sentences)
• Shape
• Force of air resistance much smaller
relative to the ball’s weight.
• Net force is almost equal to the
ball’s weight, so it falls at nearly 9.8
m/sec2 downward.
• Define.
• Terminal Speed: The maximum
speed reached by an object in
free fall; the speed at which the
force of gravity and air resistance
are equal.
Why does a crumpled ball of paper
have a faster terminal speed than a flat
piece of paper?
• The flat sheet has more air
resistance even though the
paper’s weight is the same.