Newtons Laws of Motion

1
Newtons Laws of Motion

• Kinematic equations can describe where and object
  will be and how it will move at any given time,
  but they do not address what causes the
  acceleration that changes the motion.
• Define a new concept to accomplish this task

2
Forces

• Intuitive definition something that pushes or
  pulls on an object.
• Strengths
• Stronger the push or pull, the more change in
  motion seen
• Includes direction
• Weaknesses
• Implies contact between objects is necessary
• Doesnt relate force to acceleration
  quantitatively

3
Quantifying force

• Use intuitive definition as guide
• Doubling the force doubles the acceleration
• Force and acceleration are in same direction
• Larger objects require more force than
  smaller objects for same acceleration
• Not physical size that determines large verses
  small
• heavier objects are harder to affect than
  lighter objects
• Note that heavier objects have more atoms and
  molecules, which in turn might have more
  particles in them.
• These objects are more massive than lighter
  objects.

4
Frames of Reference

• Split all frames of reference into 2 types
  inertial and non-inertial
• Inertial frames do not accelerate relative to a
  larger, fixed frame
• Non-inertial frames accelerate
• Only use inertial frames to study motion
• Acceleration of non-inertial frames acts like
  another force on objects

5
Pseudo-forces

• Surrounded by pseudo-forces
• Force pushing you back in your seat as you
  accelerate, or forward when you brake
• Centrifugal (outward) force on objects moving
  around a circle
• Coriolis force causes hurricanes to spin

6
Newtons First Law

• An object at rest will remain at rest, and an
  object in motion will continue to move in a
  straight line at a constant speed, unless acted
  upon by an net external force.

• Also known as Galileos Law of Inertia
• First discovered by Galileo by observing boats in
  Venice
• Contrary to common sense, in which moving
  objects stop unless acted upon.

7
Newtons Second Law

• When a net force acts upon an object, it is
  accelerated in the direction of the force. The
  strength of acceleration is proportional to the
  force and inversely proportional to the mass

• Mass is a measurement of inertia, or resistance
  to change in motion
• Sum of forces is important, not individual forces

8
Newtons Third Law

• Whenever object A exerts a force on object B, it
  experiences an equally strong force from object B
  back upon itself

• Commonly stated as For every action there is an
  opposite and equal reaction
• Only law of motion dealing with two objects
• Two forces called action-reaction pair, or couple