Introduction to Newton

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Introduction to Newtons Laws
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Are heavier objects harder to stop when moving
than light objects? Why do you move to the
side of a car when the car turns a corner?
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Back in the day
Aristotle tried to answer the question of why
objects fall to Earth? By explaining that objects
would seek their natural position.
-This also explain why Earth didnt move. It was
already in its natural resting place at the
center of the universe.

• 
  This was, until Copernicus
• came along and explained that the Earth orbited
  the sun.
• This was later backed up by Galileo and Newton
  when they explained forces and motion in the
  universe.

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Comparison between Aristotle and Galileo

• ARISTOTLE
• Things at rest were at their natural resting
  place.
• Objects that are moving away from their natural
  resting place need to be continuously forced to
  keep them moving

• Galileo
• Objects at rest stay at rest until something
  forces them to do otherwise.
• Objects in motion stay in motion unless something
  forces it to do otherwise

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Newtons Laws
What are Newtons 3 Laws of motion?

• 1st Law An object at rest will stay at rest,
  and an object in motion will stay in motion at
  constant velocity, unless acted upon by an
  unbalanced force. (Law of Inertia)
• 2nd Law Force equals mass times acceleration.(F
  ma)
• 3rd Law For every action there is an equal and
  opposite reaction. (All forces come in pairs)

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Newtons 1st LawLaw of Inertia
An object at rest will stay at rest, and an
object in motion will stay in motion at constant
velocity, unless acted upon by an unbalanced
force.
What does this all mean?
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What gives an object a lot of Inertia?

• Is it volume?

Volume the amount of space an object takes up
NO!!!!!!
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What gives an object a lot of Inertia?

• Is it weight?

Weight the effect that gravity has on an object
NO!!!!!!
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What gives an object a lot of Inertia?

• Is it mass?

Mass the amount of matter an object
possesses. -the amount of stuff something has
YES!!!!!!!!!!!!!!!!!
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Inertia
Inertia is an objects ability to resist a change
in motion.

• Derived from Latin meaning idleness or
  laziness

Mass is directly related to Inertia. The more
mass you have, the more inertia you have.
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Newtonss 1st Law and You
Dont let this be you. Wear seat belts. Because
of inertia, objects (including you) resist
changes in their motion. When the car going 80
km/hour is stopped by the brick wall, your body
keeps moving at 80 km/hour.
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If Newtons 1st law is true
Why then, do we observe every day objects in
motion slowing down and becoming motionless
seemingly without an outside force?
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Friction!

• In the absence of a force of friction, an object
  you
• push would continue in motion with the same speed
  
• and direction - forever! (Or at least to the end
• of the table top.)

Friction is a type of force.
A force is a push or pull. -force is a vector
quantity (it has a size and direction)
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Up until this point, we have only been dealing
with objects at rest or moving with a constant
velocity.
Can we describe the motion of objects that dont
move at a constant velocity?
Yes!!! Things that arent moving at a constant
velocity are accelerating.
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Acceleration
Acceleration is how much velocity changes in a
certain amount of time.
Acceleration is a vector quantity.
The units for acceleration are meters per second
per second, or m/s2
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Newtons 2nd Law
F ma
The net force of an object is equal to the
product of its mass and acceleration
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Newtons 2nd Law
If F ma then the units for force are kgm/s2
We call kgm/s2 Newtons (N)
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How much force is needed to accelerate a 1400
kilogram car 2 meters per second/per second?
Write the formula
Fill in given numbers and units
Solve for the unknown
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Another form of F ma
We can write this as What does this mean in
English?
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What is a net force?
The sum of all forces acting on an object in a
given direction.
1 N
3 N
2 N
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Free Body Diagrams
A free body diagram is a vector diagram that
shows how forces act on an object. - We
represent these forces with vectors (arrows) that
pull from the center of mass of the object.
10 N
5 N
If you push this box to the right with 5 N and
you push to the left with 10 N, what is the net
force on the object?
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Special types of Forces
Normal force is the force that is always
perpendicular to the surface of what ever an
object is sitting on. It generally opposes the
downward force of gravity.
When you sit in your chair, your body exerts a
downward force on the chair (your weight) and the
chair exerts an upward force on your body (known
as the Normal Force).
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Normal Force
Draw a Free Body Diagram of a 60 kg box sitting
on the floor.
F ma
FN 600 N
So m 60 kg a 10 m/s2
What is the net Force?
60 kg
F 60 kg x 10 m/s2 Fgravity 600 N
Fg 600 N
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Friction

• Friction is a force that opposes the motion of an
  object.
• In other words, friction will push in the
  opposite direction of the way an object is
  moving.
• It slows down motion!

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Friction
Draw a free body diagram of a 30 kg box sitting
on a table. It is being pushed with a 20 N force
to the right, and there is a frictional force of
15 N.
FN 300 N
30 kg
Fp 20 N
Ff 15 N
Fg 300 N
What is the net force?