Physical Science Newton

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Physical ScienceNewtons LawsAnd Forces
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• GALILEO
• Since he experimented to get EVIDENCE for his
  conclusions, he is considered to be the
• father of experimental physics.

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He also figured out that
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• Things in motion tend to STAY IN MOTION they do
  NOT tend to SLOW DOWN OR STOP ON THEIR OWN.
• In fact, Galileo figured out that it TAKES a
  force to make something slow down or stop. The
  usual force is (he discovered) FRICTION.

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• So in fact, GALILEO figured out the principle
  behind what we call
• Newtons 1st Law

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NEWTONS 1ST LAW

• An object at rest tends to stay at rest, and an
  object in motion tends to stay in motion in a
  straight line at constant velocity unless acted
  on by an outside net force.

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INERTIA refers to Newtons 1st Law

• Inertia is the TENDENCY of ANY MASS to KEEP DOING
  what it is ALREADY DOING (resting, or going in a
  straight line at a constant speed).
• A FORCE is a push or a pull, and INERTIA IS NOT A
  FORCE!!!
• IT IS A TENDENCEY OR CHARACTERISTIC!

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INERTIA

• Inertia is a measure of an objects RESISTANCE to
  CHANGE in state of motion. (Thingslike
  peopledont want to change!)
• The word inertia comes from the Italian word for
  laziness.
• Inertia is DIRECTLY PROPORTIONAL TO MASS ONLY.
  (More mass means more inertia.)
• Inertia has nothing to do with size, speed, or
  anything else.

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What is the difference between mass and weight?

• WEIGHT is the pull due to gravity.
• Weight CHANGES due to location!
• Weight is a FORCE!

MASS is the amount of MATTER in an object. Mass
does NOT change, regardless of location. Mass is
measured in kg.
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inertia

• If you are floating around in space outside the
  space shuttle, and go up to it and give it a
  kick, what will be the results?

• The space shuttle will go flying off, of course,
  since it has no weight!
• b) You will go flying off in the opposite
  direction with a hurt foot, of course, since the
  space shuttle has the same amount of mass (and
  inertia) in space as it does here on earth!

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• WHAT IS VOLUME?
• The amount of space something takes up
• WHAT IS DENSITY?
• The amount of mass per unit of volume D m / V

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• WHAT HAS MORE VOLUME A kilogram of lead, or a
  kilogram of bread?
• THE BREAD TAKES UP MORE SPACE, OF COURSE!
• WHAT HAS A HIGHER DENSITY A kilogram of lead, or
  a kilogram of bread?
• THE LEAD DOESIT IS MORE COMPACTit has more
  matter packed into a smaller space!

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What is force?

• A push or a pull.
• A NET force is the leftover (or unbalanced)
  amount of force after you add up all the forces
  acting in a certain direction.

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• What is ACCELERATION?
• A CHANGE in motion!
• That is ANY change in SPEED AND/OR DIRECTION!!!
• Only NET forces cause accelerations!
• No net force means NO CHANGE in speed or
  direction!

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Newtons 2nd Law

• The BIGGER the amount of the force,
• the BIGGER the acceleration!
• The BIGGER the mass,
• the LESS the acceleration!
• In fancy terms?
• The acceleration of a body is directly
  proportional to the net force on it, and
  inversely proportional to the mass.

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FORCE UNITS

• Think of Newtons 2nd law F m a
• N kg m/s2
• Since mass is in kg, and a is in m/s/s, or m/s2,
  F or Forces are measured in kg m/s2.
• That is the SAME as a Newton, or N.

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F ma 100N 100kg X 1.00m/s2 a
F/m 1.00m/s2 100N / 100kg
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Newtons 2nd Law

• This makes sensethe more massive something is,
  the harder it is to accelerate. And the more
  force there is, the easier something will
  accelerate.
• Zero net force means zero acceleration.

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F ma

• A 2 kg mass accelerating at 3 m/s2 has how much
  net force on it?

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SOLUTION

• A 2 kg mass accelerating at 3 m/s2 has how much
  net force on it?
• F ma 2kg X 3 m/s2 6 N

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F ma W mg

• If you weigh 150 pounds, your mass is about 68
  kg. (1 kg 2.2 lbs.) What is your WEIGHT in
  Newtons here on Earth?

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SOLUTION

• If you weigh 150 pounds, your mass is about 68
  kg. (1 kg 2.2 lbs.) What is your WEIGHT in
  Newtons here on Earth?
• W mg 68kg X 10m/s2 680 N
• F ma

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F ma a F/m

• A force of 16 N is pulling on a 2 kg wagon. If
  there is no friction, how fast is the wagon
  accelerating?

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SOLUTION

• A force of 16 N is pulling on a 2 kg wagon. If
  there is no friction, how fast is the wagon
  accelerating?
• a F/m 16N / 2kg 8 m/s2

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F ma a F/m

• If the wagon above is going at a CONSTANT
  VELOCITY with the 16N pull, how much friction is
  there?

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• SOLUTION
• If the wagon above is going at a CONSTANT
  VELOCITY with the 16N pull, how much friction is
  there?
• 16 N ! If going constant velocity, acceleration
  is 0, net force is 0 so all forces are BALANCED
  (equal)
• in any 1 direction.

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Newtons 3rd Law

• Every action has an equal and opposite reaction.
• There are NO single forces. They are always an
  action/reaction pair.

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• For example, you touch the table with 1N of
  Force, it touches you back with 1N of Force
  SIMULTANEOUSLY (not a little later!).

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• Newtons 3rd Law says that an action reaction
  pair would be hands pushing on barbell, barbell
  pushing on hands.
• Then HOW can the barbell be ACCELERATED upward?
• What OTHER action reaction pairs are involved?

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More on Newtons 3rd

• If you smash the wall with your fist with 80 N of
  force, the wall will hit you right back with 80
  N.
• But what if you hold a piece of paper in the air
  and try to hit it with 80 N?

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If the paper

• cannot support or hit you back with 80 N, can YOU
  really hit IT with 80 N?
• If the paper can only hit you back with 5 N, what
  happens to the other 75 N from your punch??!

HINT
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How do they accelerate?
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Force of friction

• Opposes motion
• Occurs between surfaces in contact

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Gravitational force

• Is the WEAKEST of all the forces, but acts over
  the GREATEST distances!

You are pulling and pulled by EVERY ATOM IN THE
UNIVERSE!!!
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Electromagnetic forces

• Are the forces that act due to electron
  configuration in atoms
• These forces are responsible for the PROPERTIES
  or characteristics of elements, compounds, and
  materials

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• This force makes paint stick to a wall, makes
  diamonds extremely hard, makes gold malleable,
  rubber stretchy, water a bipolar molecule, etc.

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