Download Newton's Three Laws of Motion

Forces
Unit 1 Lesson 3
FORCES
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Force = push or pull
Force has size and direction
Force is labeled in Newtons (N).
Forces must act on an object
Forces DO NOT always cause movement
FORCES
• When objects “bump” into each other and
have contact = contact force
• Ex. Friction- rub your hands together quickly- contact
force of friction
• Force can act at a distance
– Ex. Gravity
Multiple FORCES
• Net force- more than one force working
together
• Add them together when they are working
in the same direction
• Subtract them if they are different directions
Multiple FORCES
• When net force is zero (0) then the forces
are BALANCED
• Balanced forced will not cause movement
or change motion
• When the net force is not zero, then the
forces are UNBALANCED
• Unbalanced forces change motion (speed,
directions or both) and cause acceleration
Newton's Three
Laws of Motion
Sir Isaac Newton
• Sir Isaac Newton
(1643-1727) an
English scientist and
mathematician
famous for his
discovery of the law
of gravity also
discovered the three
laws of motion.
First Law of Motion
An object at rest stays at rest; an object
in motion stays in motion at the same
speed and direction unless it experiences
an unbalanced force.
*This law is called the Law of Inertia.
First Law of Motion
Examples
When you hit a golf ball an unbalanced force
is put on the ball causing the ball to move.
Two teams are playing tug of war.
They are both exerting equal force
on the rope in opposite directions.
This balanced force results in no
change of motion.
If objects in motion tend to stay in
motion, why don’t moving objects
keep moving forever?
Things don’t keep moving forever because
there’s almost always an unbalanced force
acting upon it.
A book sliding across a table slows
down and stops because of the force
of friction.
If you throw a ball upwards it will
eventually slow down and fall
because of the force of gravity.
In outer space, away from gravity and any
sources of friction, a rocket ship launched
with a certain speed and direction would
keep going in that same direction and at that
same speed forever.
Second Law of Motion
The acceleration of an object depends on the
mass of the object and the amount of force
applied. (Force = mass x acceleration)
Pushing an empty shopping cart is much easier than pushing a full
cart. A larger force is required to accelerate a full cart compared
to an empty one.
Smaller Force
Larger Force
Third Law of Motion
Whenever on object exerts a force on a
second object, the second object exerts an
equal and opposite force on the first.
When you drop a ball and it
hits the floor, the ball pushes on
the ground. The floor also
exerts a reaction force on the
ball causing it to bounce in the
opposite direction.
Third Law of Motion
Examples
Why does it hurt so much
when you stub your toe?
When your toe exerts a force
on a rock, the rock exerts an
equal force back on your toe.
The harder you hit your toe
against it, the more force the
rock exerts back on your toe
(and the more your toe hurts).
More examples…
• Its your turn, using your book, your brain, and the
internet, find real world examples of Newton’s 3
Laws.
• Make a list in your notebook. You need to have 10
examples of each law. *They all need to be
DIFFERENT. For example, for law one if you have
an example of hitting a golf ball then you should not
have another example that is the same such as
kicking a soccer ball. *You cannot use the examples
from the power point, but you can use examples
from the book.