Download 06 Newton`s Laws of Motion

Forces change the motion of
an object in very specific
ways.
So specific in fact that
scientist and inventor, Sir
Isaac Newton
(1642-1727)
was able to find commonality
in all things in the universe.
He was very original in
naming them the
1st, 2nd and 3rd
Laws of Motion.
These laws describe the
effects that forces have on
objects.
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Newton’s 1st Law of Motion – Inertia
INERTIA
the tendency for an object to resist its change in motion.
Basically, it wants to keep doing what it’s doing.
No mom,
I don’t
want to
go!
1st Law states that…
An object in motion tends to stay in motion,
and an object at rest tends to stay at rest
until another force acts upon that object. 2
Newton’s 1st Law of Motion - Continued
Think about it like this…the book is
sitting on the table (it is at rest).
The book will stay there until (remain at rest)
until another force moves it (the outside force).
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Newton’s 1st Law of Motion - Continued
Another way to think about it is that
the greater the mass of the object –
the greater it’s inertia – the greater
its’ resistance to move.
Which wrestler would have the
greatest inertia? Why?
Let’s look at a few examples of the 1st Law of
Motion in action!
http://www.youtube.com/watch?v=WPngMOfJcFw
http://www.youtube.com/watch?v=uOSBC0SXVR4
http://www.youtube.com/watch?v=iDGvBWmUcFU
Newton’s 2nd Law of Motion - Acceleration
When the golfer hits the ball,
where is the ball going to go?
Wherever they hit the ball,
hopefully in the direction of
the pin!
2nd Law states that…
a force acting on an object causes the
object to accelerate in the direction
of that force.
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Newton’s 2nd Law of Motion - Continued
Let’s think about this one…
if the Jorge kicks the soccer ball –
which direction will the soccer ball go?
Force causes acceleration of the object to
accelerate in the direction of that force
(the kicking of the ball).
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Newton’s 2nd Law of Motion - Continued
Another way to look at the 2nd law is that force
causes acceleration.
The greater the mass – the greater the resistance
to acceleration.
Think about it like this…
If the blue truck has a mass of 25,000kg and
the red truck has a mass of 30,000kg which
truck is going to take longer to speed up?
Right, the RED Truck because it has a greater
mass…5000kg more than the BLUE truck!
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Newton’s 2nd Law of Motion - Continued
Let’s look at a video of the 2nd
Law of Motion in action!
http://www.youtube.com/watch?v=UhCG0qoY9Dc
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Newton’s 2nd Law of Motion – The Formula
Force = Mass X Acceleration
divide
F
m
F = ma
a
multiply
Acceleration units = m/s2
Mass units = kilograms (kg)
Force units = kg.m/s2 OR Newton
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Newton’s 2nd Law of Motion – Calculations
Problem: What force is exerted on a 1000kg car accelerating
at a speed of 15m/s2?
GUESS
Read the problem, draw a picture and write down
what is given in the problem.
1000kg
GUESS
Given
M = 1000kg
A = 15m/s2
15m/s2
Write down the unknown variables in the problem.
Unknown
Equations Needed
Substitute including units
Solution
Force
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Newton’s 2nd Law of Motion – Calculations
Problem: What force is exerted on a 1000kg car accelerating
at a speed of 15m/s2?
GUESS
Given
M = 1000kg
A=
15m/s2
Write down the equation needed to solve the problem.
Unknown
Force
Equations Needed
F = ma
Substitute including units
F = 1000kg x 15m/s2
Solution
F = 15,000
kg.m/s2 OR
F = 15,000 N
GUESS
Substitute the known variables into the equation
including the UNITS.
GUESS
Solve the equation including the UNITS.
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Do problems 1-3 in
your notes.
Using all the correct
steps!
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Newton’s 2nd Law of Motion – Gravity
The acceleration for any object
moving under the sole influence of
gravity on Earth is 9.8m/s2.
Any moving object being acted upon
ONLY by the force of gravity is
said to be "in a state of free fall”
because these objects do not
encounter air resistance.
9.8m/s2
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Newton’s 2nd Law of Motion – Gravity Diagram
Assuming that the position of
a free-falling ball dropped
from a position of rest is
shown every 1 second, the
velocity of the ball shown to
increases as the time
increases.
What relationship do you notice
about the distance per every 1
second?
So…what type of acceleration
does the ball have? Positive or
Negative.
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Newton’s 2nd Law of Motion – Gravity
More on this later when we discuss
potential and kinetic energy….
But for now, all you need to remember is
that acceleration for any object moving
under the sole influence of gravity on Earth
is 9.8m/s2.
15
Newton’s 3rd Law of Motion – Action/Reaction
3rd Law states that…
for every ACTION, there is an equal
and opposite REACTION.
Action / Reaction forces act in PAIRS.
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Newton’s 3rd Law of Motion – Continued
In this example, when the lady is
walking, her feet push against the
ground while the ground pushes
against her feet.
Thus action/reaction – pair is
the feet and ground pushing off
of one another.
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Newton’s 3rd Law of Motion - Continued
Another example:
Let’s think about this one…what
are the pairs of forces that are
acting against each other in
order for the shuttle to launch?
Let’s look at how the 3rd Law of Motion
made the NASA affected the astronauts.
http://www.youtube.com/watch?v=PrJnWTcW55s
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Newton’s 2nd Law of Motion – Momentum
The property
of a moving
object due to
both its mass
and its velocity.
MOMENTUM
An increase in
either mass or
velocity causes
an increase in
momentum.
For example, if both football players had the
same mass of 95kg, but the one in the Yellow
helmet was traveling at 10m/s and the one in
the Orange helmet was traveling at 12m/s,
would that make a difference?
Let’s find out…
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Newton’s 2nd Law of Motion – Momentum Formula
Momentum = Mass X Velocity
divide
P
m
P = mv
v
multiply
Velocity or Speed units = m/s
Mass units = kilograms (kg)
Momentum units = kg/m/s
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Newton’s 2nd Law – Momentum Calculations
Problem: What is the momentum of the football players in the
orange and yellow helmets? Which player has the
greater momentum?
G U E S S in order to solve the problem!
Remember both players had the same
mass of 95kg, but the one in the Yellow
helmet was traveling at 10m/s and the one
in the Orange helmet was traveling at
12m/s.
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Newton’s 2nd Law – Momentum Calculations
GUESS
Given
Read the problem, draw a picture and write down
what is given in the problem.
V = 10m/s
V = 12m/s
M = 95kg
M = 95kg
Unknown
V = 12m/s
M = 95kg
Momentum
V = 10m/s
Momentum
M = 95kg
GUESS
Equations Needed
Substitute including units
Solution
Write down the unknown variables in the problem. 22
Newton’s 2nd Law – Momentum Calculations
Given
V = 12m/s
M = 95kg
V = 10m/s
M = 95kg
Unknown
Momentum
Momentum
Equations Needed
Substitute including units
Solution
P = mv
P = 95kg x 12m/s
P = 1140
kg.m/s
P = mv
P = 95kg x 10m/s
P = 950
kg.m/s
GUESS
Write down the equation needed to solve the problem.
GUESS
Substitute the known variables into the equation including
the UNITS.
GUESS
Solve the equation including the UNITS.
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Newton’s 2nd Law – Momentum Calculations
Back to our original questions…
Problem: What is the momentum of the football players in the
orange and yellow helmets?
P = 1140 kg.m/s
P = 950 kg.m/s
Which player has the greater momentum? Orange
Even though they had the same mass, did it make a
difference that the orange player was traveling at a
greater velocity in terms of momentum? Absolutely!
24
Do problems 4 & 5 in
your notes.
Using all the correct
steps!
25
In the examples given in
your notes, identify if they
are representing Newton’s
1st, 2nd or 3rd Laws or
multiple laws.
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