Newtons Laws and Force

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Newtons Laws and Force
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Newtons Law of Motion

• Isaac Newton developed his laws of motion in the
  mid 1600s.
• Much of his work is based upon the published
  works of others such a Galileo and Keppler

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Newtons First Law

• If all forces acting on an object are balanced,
  that is opposing forces cancel each other out,
  then its velocity remains constant.

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Newtons First Law

• This does not mean that balanced forces result in
  no motion, rather they result in no CHANGE in
  motion
• The velocity of the object may be zero (stopped)
  or it may be moving at a constant velocity

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Newtons First Law

• Also called the law of inertia
• Inertia is the resistance to a change in motion
• The greater an objects mass, the more inertia it
  has.

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Newtons Second Law

• The first law is about what happens when all the
  forces cancel each other out i.e. they are
  balanced.
• The second law is about what happens when one
  force is greater than another, i.e. they are
  unbalanced

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Newtons Second Law

• If a net external force (unbalanced) acts upon an
  object, it will accelerate.

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Newtons Second Law

• The acceleration will be directly proportional to
  and in the direction of the force and inversely
  proportional to the mass.

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Newtons Third Law

• An objects motion does not change in isolation.
• In fact, as described by the first two laws, most
  object tend to have multiple forces acting upon
  them.
• The third law describes how objects exerting
  forces on one another interact.

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Newtons Third Law

• When objects interact, the force exerted by one
  object is equal in magnitude, but opposite in
  direction to the force exerted by the other.

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Newtons Third Law

• As you step forward off of a boat while it moves
  backward. . .
• As you stand on a skate board and push backward
  on the ground to move the board forward . . .
• As you walk . . .
• The third law of motion is acted out!

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Newtons Second Law

• When a rocket takes off, the hot gases of the
  rocket engine are pushed out of the rocket In
  response, the molecules of hot gas push upward on
  the rocket.

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Newtons Laws

• Basics F m a
• F force (Newton)
• m mass (kg)
• a acceleration (m/s2)
• So, 1 N 1 kgm/s2
• If the units of mass, distance and time are not
  in agreement, YOU MUST CONVERT THEM

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Newtons Laws

• Free Body Vector
• Diagram Diagram
• R

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Newtons Laws

• Finding R and q
• R
• Use Pythagorean Eqn
• and Tangent

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q
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Newtons Laws

• Finding Components when you know R and q
• R Fy
• Fx
• Use Sin and Cos

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q
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Newtons Laws

• Problem set A due Thursday

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Newtons Third Law

• Terminal velocity the maximum velocity reached
  by a falling object
• Gravity causes a free falling object to
  accelerate (Second Law Fma) . . .
• But as the velocity increases, the force of air
  resistance increases (Third Law). . .
• Until it balances gravitys force and the object
  falls at a constant velocity (First Law)

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Newtons Third Law

• One very effective example of the terminal
  velocity is a parachute.
• The chute catches the air, increasing resistance
  . . .
• So the velocity is slower.

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Newtons Third Law

• Quiz Wednesday!
• Do your study guide and know it so you dont have
  to be afraid!

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Forces Weight

• Weight is the force of gravity acting on an
  object. (Fwt)
• Since it is caused by gravity, what direction is
  weight?

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Forces Normal Force

• Normal is the big time physics word for
  perpendicular.
• The normal force (FN) is the force perpendicular
  to the surface.
• If the surface is level, what direction is
  normal?

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Forces Friction

• Friction is the only force that does not cause an
  object to increase its velocity.
• So, if F ma, how can it be a force?

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Forces Friction

• Friction is a resisting force due to the
  interaction of two surfaces.
• Its formula is Ff m FN
• FN is the normal force it involves the force
  holding the surfaces together

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Forces Friction

• Remember, FN is the normal force it involves the
  force holding the surfaces together

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Forces Friction

• mu (m) is the coefficient of friction and
  quantifies how the surfaces interact.

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Forces Working Problems
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Forces Working Problems
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Forces Working Problems
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Forces
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