# 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
 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
    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
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.
referring to Newton’s
Laws.
Now remove the floor
and draw the forces
acting on you.