Mechanics Kinematics and Newton's Laws by umsymums37

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									Newton’s Laws
   of Motion
 (and force!!)
A force is a push or pull on an object
   control over movement:
    desired motion
    or preventing undesirable movement
       EXAMPLES of forces:
            Contact Forces
  muscles
  machines/mechanical
         ropes and wires
   Friction  adhesion
 EXAMPLES    of FORCES TOO:
  Non-contact   forces:

 Nuclear
 Electrical/magnetic
 Gravity  weight
Non-contact
Forces
such as
gravity,
magnetic, and
electric
forces.
 Like   Velocity and Acceleration…..

FORCE has both magnitude
       AND
       Direction!!!
   Net FORCE (unbalanced force)
          results in motion (for an
  object at rest), or a change in velocity of
  the object already in motion
    Equilibrant Force
           Net Force = 0 …..means,
               an object at rest remains
  at rest OR an object moving with
  constant motion will continue at that
  constant motion.
 FORCE IS MEASURED IN NEWTONS
 One NEWTON (N)  1 kg x 1m
                       s2
Think about it….
              Force = mass X acceleration

 thatgives a 1 kg object, an acceleration
  of 1m/s2
 Inertia tendency of an object to
  RESIST a change in motion
    Example: velocity of an object
  remains constant unless a force
  changes it
           the greater the mass, the
  greater the inertia
Newton’s First Law of Motion
   An object continues in a state of rest
   or in a state of motion at constant
   speed along a straight line…
                  unless compelled to change
                  that state by a net force.

                                an object
                                moving at a
                                constant velocity
                                remains at that
                                velocity unless a
                                NET FORCE
                                (>0) acts upon it
Inertia plays
a central role
in one type of
seat belt
mechanism.
 Friction    force of adhesion
               depends on the surface
  and force acting between surfaces
     EXAMPLES OF FRICTION: air,
  fluid, solids
The Normal Force & Friction
The Normal Force & Friction
       Newton’s Second Law of Motion
When a net force F acts on an object
of mass m, the acceleration a that
results is directly proportional to the
net force and is inversely proportional

                                                F
to the mass.

If: net F = m X a            then….          a
                                                         m
direction of acceleration = direction of the net force

    SI Unit of Force: kg • m/s2 = newton (N)
AND ONCE AGAAAAAINNN!!!
A NEWTON (not the “fig” variety)
   ….is the amount of force
   required to accelerate a
      1 kg object 1 m/s2
               m = 1850 kg
                             With two guys pushing…….
                                      What are
                                  the net forces???




 F  + 275 N + 395 N  560 N = +110 N
     a
          F   110 N  0.059 m/s              2

           m         1850 kg
If the airplane’s mass is 13 300 kg,
what is the magnitude of the net
force that the catapult and jet
engine exert on the plane?
                  F  ma  (13 300 kg)(31m/s )
                                             2


                       = 4.1105 N
The Normal Force
GRAVITY (gravitational force)
 the pull an object exerts on another object
           the amount of gravitational force
  is dependent on:
                 1) Mass of the two objects
                 2) distance between objects
  the greater the mass, the greater the
  gravitational pull on that object
 Weight  measure of gravitational force
  varies dependent on proximity to EARTH

      Weight vs Mass
Mass  is the measure of…
the matter of an object
      AND
an object’s resistance to
  change in motion
Newton’s Third Law of Motion
 Whenever a body
 exerts a force on a
 second body, the
 second body exerts
 an oppositely
 directed force of
 equal magnitude
 on the first body.
Newton’s          3 rd   Law……
 action force = reaction force
  for every action, there is an equal and opposite
  reaction!!
EXAMPLES:
   tires of a car push against the road, and the road
  in turn pushes back on the tires,
                    OR
  a swimmer pushes the water backward, and the
  water pushes swimmer forward

in both examples, the net Force is > Zero, otherwise
   the object wouldn’t move!!!
Newton’s Third Law
For every action there is an equal and
    opposite reaction.
        Free Body Diagrams
A Free Body Diagram distills the
  problem’s complexity down to only
  those actions that are interacting with
  the object of interest.
Consider the following
 situation: You are
 standing in the middle
 of the room.

Are there any forces
   acting on you?
Is there net force acting
   on you?
Draw the forces acting
   on you.
Justify your answer by
   referring to Newton’s
   Laws.
Now remove the floor
 and draw the forces
 acting on you.

 What is your state of
 motion now?

Characterize it by
 stating something that
 we can calculate.

								
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