Transcript Newton`s First and Second Laws

Key Concepts
•What is Newton’s first law of motion?
•What is Newton’s second law of motion?
Key Terms - Inertia
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An object at rest will remain at rest, and an
object moving at a constant velocity will
continue moving at a constant velocity,
unless acted upon by an unbalanced force
Clothes on the floor will stay there unless
someone uses a force to pick them up
A tennis ball that was hit will continue until a
force stops it
Gravity and friction are the 2 forces on Earth
that often change an object’s motion
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Tendency of an object to resist a change in
motion
Newton’s first law is also called the Law of
Inertia
Example – a person continues to move
forward when a car stops
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The greater the mass of an object, the greater
the inertia
The greater the inertia, the greater the force
needed to move the object, and the greater
the force needed to change its motion
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Acceleration depends on
the object’s mass and the
net force acting on the
object
Acceleration = Net Force
Mass
 Force = mass * acceleration
Units = Newton (N) = kg
*m/s2
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Calculating Force: A speedboat pulls a 55kg water
skier. The force causes the skier to accelerate at
2.0m/s2. Calculate the net force that causes this
acceleration.
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Information given:
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What quantity are you trying to calculate?
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◦ Mass of water skier =55kg
◦ Acceleration of water skier= 2.0 m/s2
◦ Net force Fnet
What formula should you use?
A = fnet
or Fnet = m*a
m
Perform calculation – 55kg *2.0m/s2 = 110kg*m/s2
= 110N
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What is the net force on a 1,000 kg object
accelerating at 3 m/s2?
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What net force is needed to accelerate a 25
kg cart at 14m/s2?
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If you keep the mass constant, a change in
force will have the same change in the
acceleration
If you keep the force constant, an increase in
mass will cause a decrease in acceleration
Opposite is also true – If the force is constant,
a decrease in mass will cause an increase in
acceleration
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http://www.physicsclassroom.com/class/new
tlaws/u2l1b.cfm
http://www.rcs.k12.va.us/csjh/sieber/Physic
alSci_1stSem.htm