Transcript Newton`s Second Law of Motion

Newton’s Laws of Motion
Learning Objectives
 State Newton’s first law of motion.
 State Newton’s second law of motion.
 State Newton’s third law of motion.
Warm up
 Define these words
 inertia
10/30
Isaac Newton
“If a horse draws a stone tied to a
rope, the horse (if I may so say)
will be equally drawn back towards
the stone....”
—Sir Isaac Newton
Newton’s First Law of Motion
An object at rest will remain at rest unless acted upon by a
nonzero net force
AND
an object moving at a constant velocity will continue moving at a
constant velocity unless acted upon by a nonzero net force.
Inertia: resistance to
change in motion
At rest
Constant motion in a straight line
Inertia Depends on Mass
The greater the mass of an object, the greater its inertia
and the greater the force required to change its motion.
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3
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Newton’s Second Law of Motion
An object’s acceleration depends on its mass and on the net
force acting on it.
Si Unit: Newtons (N)
Newton’s Second Law of Motion
The sled’s acceleration will increase if:
passengers are removed to
decrease the mass.
more dogs are added to
increase the force.
OR
Newton’s Second Law of Motion
Practice:
What is the net force on a 1,200-kg
race car accelerating at a rate of
3 m/s2?
3,600 N
Newton’s Third Law of Motion
If one object exerts a force on
another object, then the second
object exerts a force of equal
strength in the opposite direction
on the first object.
For every action, there is an
equal and opposite reaction.
Action
Reaction
Action-Reaction Forces
Force on hands
Force on ball
Force on ball
Laws of Motion in Action
1. Use one of Newton’s laws to explain why the driver was
thrown forward when she braked.
Newton’s first law says that objects
in motion stay in motion. The car
stopped, but the driver’s inertia
kept her moving forward.
Laws of Motion in Action
2. Use one of Newton’s laws to explain how the seat belt
stopped the driver’s body from moving too far forward.
Newton’s third law says that for every
action force, there is an equal and opposite
reaction force. The driver’s body exerted
an action force on the seat belt. The seat
belt exerted a reaction force on the driver
that stopped her motion.
Laws of Motion in Action
3. Use one of Newton’s laws to determine how much force
the driver will need to exert to make it to her appointment
on time.
Newton’s second law is represented by
the formula F = ma.
F = (1,100 kg)(2 m/s2)
F = 2,200 N
Patterns in Newtons Laws
Q: What pattern of motion identifies with the law of inertia?
• A: objects resist a change in their motion
Q: What pattern exists in the law of force and acceleration?
• A: as force increases, so does acceleration if the mass is
constant
• A: as acceleration increases so does force if the mass is
constant
• A: As mass increases, acceleration decreases if the force
is constant
• A: As mass decreases, acceleration increase if the force is
constant
Patterns in Newtons Laws
Q: What pattern exists in the law of action-reaction?
• A: Every action force has a corresponding reaction force
Q: What are the action- reaction forces?
• A: Whenever one object exerts a force on a second object,
the second object exerts an EQUAL and OPPOSITE force
on the first object.