Transcript WHAT IS FORCE?

WHAT IS INERTIA?
Newton’s Laws
Standard 8-5.6
Summarize And illustrate the
concept of inertia.
Newton’s First Law of Motion
(“the law of inertia”)
An object at rest will remain
at rest unless acted on by
an unbalanced force.
An object in motion
continues in motion with
the same speed and in the
same direction unless
acted upon by an
unbalanced force.
WHAT IS INERTIA?
The tendency of an object to resist change in its
motion.
Whether an object is moving or at rest, every object resists any
change to its motion.
Examples:
**Air hockey puck will ride on air once you push it
** Tennis ball flies through the air once you hit it with a racket
In both of these cases, the object continues to move even
after you remove the force.
Inertia explains common events like:
When you are in a car and stop suddenly,
you will continue to move forward.
(WHY YOU NEED TO WEAR SEAT
BELTS!!)
Passengers in a moving car have inertia. Therefore a
force is required to change their motion. That force is
exerted by the safety belt. If the safety belt is not
worn, that force is exerted by the windshield instead.
What is more difficult to move?
A 1 quart jar of pennies or a 1
quart jar of feathers?
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Obviously the pennies…. Why?
What is the difference between a quart of
pennies and a quart of feathers?
Both jars occupy the same amount of
space and have the same amount of
volume.
The difference is the amount of MASS.
What is Mass?
Mass is the amount of matter in an
object.
The amount of inertia an object has
depends on how much mass it has.
The greater the mass of an object,
the greater its inertia!!
Mass can also be defined as a measure of the inertia of
an object.
Newton’s 2nd Law of Motion
• The net force on an object is equal to the
product of it’s acceleration and mass.
• Force = Mass x Acceleration
– Remember, the unit of force is a Newton.
• Acceleration is the rate at which velocity
changes.
Newton’s Second Law of Motion
• Acceleration will increase when you
increase the FORCE on the object.
• Acceleration will increase when you
decrease the MASS of an object.
Examples:
• You are pulling a wagon with two dogs in
the back. If one dog jumps out, will the
acceleration increase or decrease?
• Suppose you know the acceleration of a
shopping cart as it rolls down a super
market isle. You want to find the force
with which it was pushed. What other
information do you need in order to find
the force?
Newton’s Third Law of Motion
• Newton’s third law states that 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.
• In other words, every action has an
equal, but opposite reaction.
Newton’s Third Law of Motion
• A squid applies Newton’s third law of
motion to move itself through the water.
– When a squid pushes water out, the expelled
water pushes back and forces the squid to
move ahead.
Water pushed out is the
action.
Squid being propelled
forward is the reaction.
Newton’s Third Law of Motion
• When a rocket lifts off from the ground.
– The force of the air pushing out of the rocket
towards the ground propels the rocket in the
opposite direction
Reaction Force
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Action Force