Define MOTION
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Motion:
Change in position of an
object relative to a reference
point.
Describe SPEED and
VELOCITY
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• SPEED - is the rate of motion, or the
rate of change of position;
– a measurement of distance traveled over
time
– calculated by dividing the distance traveled
by the time taken
• VELOCITY - measurement of the rate
and direction of motion
– an object's speed and direction of motion
Describe
Friction
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FRICTION - the resistance to motion
encountered when one body is moved in
contact with another
Force opposing motion of two objects that are
in contact.
Describe
ACCELERATION
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• ACCELERATION - The rate at
which an object's velocity changes with
time.
– The rate of change of velocity.
– Change in speed or change of direction.
Create a diagram of a
distance-time graph and
a velocity-time graph
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A student stands on a skateboard as the skateboard
remains in place. When the student pushes his foot against
the ground, the skateboard moves forward. The harder he
pushes against the ground, the faster the skateboard
moves. A friend jumps on for a ride, and the skateboard
slows down. The student must push even harder to get the
skateboard moving again. Once they get going, they hit a
curb. The skateboard stops moving, but the students fly
onto the grass. Fortunately, everyone is fine.
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– Describe three instances in the above paragraph where
the skateboard was under the influence of unbalanced
forces. For each instance, identify the primary forces
involved, and explain why they were unbalanced.
Three situations where the skateboard is under
the influence of unbalanced forces are:
1. The student giving the initial push to move
the skateboard — unbalanced between
acceleration by the student and friction, as the
skateboard started moving.
2. Friend jumps on the skateboard —
unbalanced between acceleration by the
student and friction, as the skateboard started
slowing down.
3. Hitting the curb — unbalanced between
acceleration by the student and force exerted
by the curb, as the skateboard stops moving.
A group of students split up into two groups of
four for a tug-of-war. Each group pulls on one
end of a heavy rope.
– Draw a diagram showing what happens when
the forces on the rope are balanced. The forces
involved should be represented by arrows, and
any motion should be drawn and labeled. Your
diagram should include the students pulling on
the rope.
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A person jumps out of an airplane. At first, the
person speeds up during the fall. But then, the
person falls at a constant velocity known as
terminal velocity.
– Identify the two primary forces acting on the
person during the fall.
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The person experiences the primary
forces of gravity and air resistance
during the fall.
Explain inertia
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An object in motion will remain in
motion (keep moving), and an
object at rest will remain at rest
(not move) unless acted upon by
an outside force.
A student
stands on a skateboard as the skateboard remains in place.
When the student pushes his foot against the ground, the skateboard
moves forward. The harder he pushes against the ground, the faster the
skateboard moves. A friend jumps on for a ride, and the skateboard slows
down. The student must push even harder to get the skateboard moving
again. Once they get going, they hit a curb. The skateboard stops moving,
but the students fly onto the grass. Fortunately, everyone is fine.
– Describe three instances in the above paragraph where the skateboard
was under the influence of unbalanced forces. For each instance, identify
the primary forces involved, and explain why they were unbalanced.
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Three situations where the skateboard is under
the influence of unbalanced forces are:
1. The student giving the initial push to move
the skateboard — unbalanced between
acceleration by the student and friction, as the
skateboard started moving.
2. Friend jumps on the skateboard —
unbalanced between acceleration by the
student and friction, as the skateboard started
slowing down.
3. Hitting the curb — unbalanced between
acceleration by the student and force exerted
by the curb, as the skateboard stops moving.
A student stands on a skateboard as the skateboard
remains in place. When the student pushes his foot against
the ground, the skateboard moves forward. The harder he
pushes against the ground, the faster the skateboard
moves. A friend jumps on for a ride, and the skateboard
slows down. The student must push even harder to get the
skateboard moving again. Once they get going, they hit a
curb. The skateboard stops moving, but the students fly
onto the grass. Fortunately, everyone is fine.
Describe one instance in the above paragraph where
the skateboard was under the influence of balanced
forces. Identify the primary forces involved, and explain
why they were balanced.
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1
A situation where the skateboard is under the
influence of balanced forces is:
1. The student standing on the skateboard as
it remains in place — balanced between
gravity and force exerted by the ground, as the
skateboard remains motionless.
The speed of a person riding a
bicycle on a level, straight road is
measured and plotted in the above
graph.
– Identify and describe the two
primary factors acting on the bike
that affect its speed for each of the
following time periods:
– 0 min. to 1 min.
– 1 min. to 2 min.
– 2 min .to 3 min.
– 3 min. to 4
min.
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Acceleration by the biker and the friction are the
primary forces acting on the bike that affect its
speed.
During period 1, the forces are unbalanced,
because the bike is slowing down.
During period 2, the forces are balanced,
because the bike's speed stays constant.
During period 3 the forces are unbalanced,
because the bike is speeding up.
During period 4, the forces are balanced,
because the bike's speed stays constant.
In what direction is the force of
friction exerted?
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The force of friction is exerted opposite to
the direction of motion
What are two ways you can
change your velocity?
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Change speed or change direction
What is a net force?
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A net force is the sum of the
forces acting on an object
Describe work
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Work is done when a force
causes an object to move in
the direction of the force.