Transcript Newtons First Law

Come on People
This is not rocket
science
Oh, Wait
Yes it is!
Newtons First Law
Chapter 6
Section 2
Tuesday, March 29, 2016
Force
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An objects movement changes in
response to a force
A force is a push or a pull
Can be a contact force
• A push or a pull
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Can be a long range force
• Gravity
• Magnetism
Newton's First Law of Motion
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An object at rest stays at rest unless
acted on by an outside force
An object in motion stays in motion
unless acted on by an outside force
Force
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SI unit for force is the Newton (N)
About the force needed to lift 4
ounces of water
Newtons First Law
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An object in motion tends to stay in
motion unless acted on by an outside
force.
An object at rest tends to stay at rest
unless acted on by an outside force.
Also known as inertia
Inertia and Mass
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The more mass an object has the more
inertia it has
The more inertia an object has, the
harder it is to change its motion.
So lets look at Football Physics
Which would be better as a football
lineman?
Why?
Adding Forces
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The motion of an object changes only
if a force is acting on it
More than one force can act on an
object
If forces act in opposite directions
with equal force, no motion happens
Balanced Forces
Adding Forces
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If one force is greater than the other
the object will move in the direction
of the larger force
Motion only changes if forces are
unbalanced
Motion changes in the direction of
the greater force
Newton’s Second Law
Chapter 6
Section 3
The Second Law of Motion
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Used to predict Motion
An object acted on by an unbalanced
force will accelerate in the direction
of the force
This law is actually a formula
The Second Law of Motion
Acceleration = Force / Mass
Or
Force = Mass x Acceleration
Or
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F=MA
Force Measured
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The SI Unit for Force is the Newton
One Newton of Force will cause 1 kg
of Mass to Accelerate at 1M/S2
So 1N = 1M/S2/kg
Sample Problem
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A child has a mass of 71kg
Her Bike has a mass of 9 kg
They accelerated at a rate of 3.2M/S2
How much force was applied?
Well, force equals mass times
acceleration
So F = 80kg x 3.2M/S2 = 256
kg/M/S2
Or 256N
Force of Gravity
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Gravity is a force
The force of Earth’s gravity causes all
objects to accelerate at the same
rate when falling
The rate is 9.8M/S2
NASCAR Physics
“Physics is good stuff”
What in the wide, wide world of sports has
this stuff got to do with racing???
Well…..
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In scientific terms acceleration and
mass are inversely related.
If the force is the same (Like say
from the engine)
The more mass you have, the less
acceleration you get
Or the heavier the car, the slower the
acceleration given the same amount
of horsepower
So, which would be better as a
racecar driver?
Why?
That was heavy!
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Speaking of heavy
That leads us to weight
So wait around for the next
fascinating fact
The Bigger They Are The Harder
They Fall (But Not Faster)
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Weight = Mass X Acceleration due to
Gravity.
So…
If your mass is 60kg
60kg x 9.8 M/S2 = 588N
In science, weight is expressed as
Newtons
Silly Scientists!
Say What???
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Because weight is the force caused
by gravity acting on mass.
The same force is acting on you
whether you are falling or standing
on the ground.
Mass and Weight
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In common language mass and
weight are spoken of as the same
thing.
In zero gravity you have no weight
(that’s why we call it weightless)
But you have the same mass.
On the moon, you would have about
1/6th of you earth weight but the
same mass
A balance is used for measuring
mass because a balance
compares an object's mass to a set
of standard masses
A spring scale is used for measuring weight
because a spring scale measures the force of
gravity pulling objects downward.
1kg of bananas
weighs 9.8N on Earth.
1 kg of bananas have a
mass of 1.0 kg on Earth.
1kg of bananas
weighs 3.7N on
Mars.
1 kg of bananas have a
mass of 1.0kg on Mars
(even if they're Martian
bananas)
Football Physics
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Would the
advantage be the
same on the
moon?
Yes, the mass is
the same, the force
is caused by mass
not weight.
Friction
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A force that resists motion
But is essential to our lives
Could you get here without friction
No
Why?
Without Friction…
Moving is a bear
Three Types of Friction
Static Friction
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Why does the food
not slide off the
tray when the
waiter starts or
stops?
Static friction
resists movement
relative to the tray.
Sliding Friction
Will the glass make it?
What will slow it down?
What will make it slide better?
Rolling Friction
Air Resistance