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Force, Motion
and Energy
Force
• Any push or pull on an object
• Act in pairs
• Measured in Newtons (N)
• Every force has a magnitude and direction
• Forces can work together or against each
other
• Forces can be balanced or unbalanced
Balanced Forces
• Occurs when there is NO CHANGE in an
objects motion
• No acceleration – no change in motion
– objects are at rest or traveling at a
constant speed and direction.
Balanced forces
Unbalanced Forces
• Always cause a change in motion Acceleration
• Acceleration – change in speed or
direction of an object
•
•
•
•
•
Starting
Stopping
Speeding up
Slowing down
Turning
Net Force
• Combination of all forces acting on an
object.
• Add forces working in the same
direction.
• Subtract forces that are working in
opposite directions.
Vectors
• Lines with arrows that show force.
• Length of the line shows the amount of
force (magnitude)
• The arrow shows the direction of the
force.
Add forces acting in the
same direction
• Net Force: 14 Newtons (8+6=14)
• Direction of Force: Right
Subtract forces acting in
opposite directions
• Net Force: 2 Newtons (20-18=2)
• Direction of Force: Left
Net Force = 0
Forces are balanced
• Net Force = 0 Newtons (20-20=0)
• Forces are balanced - No change in motion
Net force and direction
• What is the net
force?
• What is the
direction of the
force?
• Why?
Newton’s Law of Inertia
Newton’s 1st Law of Motion
• An object at rest will stay at rest
unless acted on by an unbalanced force.
And
• An object in motion will stay in motion
at the same speed and direction unless
acted on by an unbalanced force.
What does this mean?
• Because of inertia, an object will keep
doing what it is doing unless forces
become unbalanced.
• Inertia is an object’s tendency to resist
change in motion
Law of Inertia (1st law)
The car stops but the man keeps
going because of inertia
Vehicle Restraints
• Describe how Newton’s 1st Law of
motion applies to vehicle restraints.
– Vehicle restraints, such as seat belts, are
the unbalanced force that stops you when a
car stops suddenly so that you don’t go
flying forward.
– This applies to all vehicle restraints.
Newton’s Law of Acceleration
• Newton’s 2nd Law
• The acceleration of
an object by a force
proportional to the
mass of the object
and directly
proportional to the
force applied.
What does this mean?
• The acceleration of an object depends
on the mass of the object and the
amount of force applied to the object.
• Acceleration is any change in motion!!!
– Starting, Stopping, Speeding up, Slowing
down, and changing directions (turning)
In other words…
• The less massive an object the greater
the acceleration
• The more massive an object the smaller
the acceleration.
• The less force applied the smaller the
acceleration
• The more force applied the greater the
acceleration.
Force = Mass X Acceleration
Calculate Force
Force = 1,000 kg X .05 m/s/s
Force = 50 Newtons
Practice Calculating Force
Which object would exert the greatest
amount of force?
– A 500 g object accelerating at 10m/s2
or
– A 10 g object accelerating at 10m/s2
– Use your formula chart to calculate Force
Force = Mass x acceleration
Answer
• 500g X 10 m/s2 = 5000 Newtons force
• 10g X 10 m/s2 = 100 Newtons of force
• The 500g object exerts a greater force
of 5000 Newtons.
Acceleration
• The rate of change in the motion of an
object.
• includes the velocity, speed and/or direction of
an object.
– Stopping, starting, speeding up, slowing down and
changing directions
• How to calculate Acceleration
– Acceleration = Force/Mass
• Measured in meters/sec2
Answer the following Questions
• If the mass of an object increases and
the force stays the same, what will
happen to the amount of acceleration?
– Acceleration will Decrease
• If the mass of the object decreases
and force stays the same, what will
happen to the amount of acceleration?
– Acceleration will Increase
What if the acceleration has to
stay the same?
• What will have to happen to the amount
of force needed if the mass of an
object increases?
– It would have to INCREASE
• What will happen to the amount of
force needed if the mass of an object
decreases?
– It would have to DECREASE
Newton’s Law of Action/Reaction
Newton’s 3rd Law of Motion
For every action, there is an equal
and opposite reaction
What does this mean?
• All forces act in pairs.
• An Action force causes a Reaction force that
is equal in size and opposite in direction.
Rocket Launches and Newton’s
Law of Action/Reaction
• A rocket taking
off creates an
action force of
gasses pushing
down that causes
the reaction
force of the
rocket going up.
Speed
• The rate at which an object covers a
distance (how fast an object moves)
Calculating Speed
Speed = distance/time
Practice Calculating Speed
• While on vacation, Lisa Carr traveled a
total distance of 440 miles. Her trip
took her 8 hours. What was her
average speed?
• Speed = 440 miles/8 hours
• Average speed = 55 miles/hour
Velocity
• Velocity tells an
objects SPEED and
DIRECTION!!!
– It includes the
direction an object
is moving as well as
the distance
traveled in a given
time (speed)
Calculating WORK
• Work is equal to the amount of force it
takes for an object to move a distance.
• Formula: Work = Force X Distance
• Work is measure in Joules
(Newton/meters)
Practice Calculating WORK
• How much work does it take to move a
box with 50 Newtons of force 10
meters?
Work = Force X Distance
50 X 10 = 500 Joules
Answer - 500 Joules
Range
• Range is the difference between the
highest and lowest values in a set of
data.
• Calculate the range of the following
test scores
– 89, 73, 84, 91, 87, 77, 94
– Subtract the lowest score from the
highest
• 94 – 73 = 21
• The range of these test scores is 21 points
Kinetic vs Potential Energy
• Kinetic Energy – Energy of motion
– The faster you are travelling the more
kinetic energy you have
• Potential Energy – Stored energy
– The more stored energy you have built up
the more potential energy you have
Where does the rollercoaster have
the greatest kinetic energy?
Where does the roller coaster have
the greatest potential energy?