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					TAKS Objective 5: Day 2
  Energy

 Isthe ability to
  do Work
 Two Types:
   Kinetic (Energy
    of Motion) and
   Potential
    (Stored Energy)
Law of Conservation of Energy
   Energy can change
    forms, but is never
    created nor destroyed
   Loss in one form =
    gain in an another
    form
   A falling object speeds
    up as it falls to the
    ground; PE decreases
    as KE increases. The
    KE it has at impact =
    the PE it had before it
    fell.
Forces and Motion
   Forces can create
    changes in motion
    (acceleration)
   Deceleration is negative
    acceleration
   Motion can be described simply

 Motion  is a
  change in an
  object’s position
 Average velocity
  (speed) is the
  change of
  position of an
  object over time
  Velocity Graphs                        V = distance
                                                time

 Velocity(v) is                               Velocity
 the slope (rise
 over run) of a                   60




                   Distance (m)
 position (d)                     40                        Series1
 vs. time (t)                     20                        Series2

 graph                            0
                                       1 3 5 7 9 11 13 15
                                            Time (sec)
40 The diagram represents the total travel of a
teacher on a Saturday. Which part of the trip is
made at the greatest average speed?
FQ
GR       How do we work this one?
HS
         Calculate v = d/t for each segment.
J T
Acceleration is a change in an objects
velocity (speed or direction)

   When an object’s
    speed changes
    over time it is
    accelerating (or
    decelerating)
   A = vfinal – vinitial
             time
   Units for
    acceleration m/s/s
    or m/s2
       Acceleration Graphs
   Acceleration (a)                                      Acceleration
    is the slope of a




                        Velocity ((m/s)(m)
    velocity (v) vs.                         60
    time (t) graph                           40
   Plotted on a                             20
    distance vs. time                         0
    graph,                                        1   3    5   7    9       11   13   15
    acceleration is                                            Time (sec)
    an exponential
    curve
Forces
A pull or push
 (or lift) that
 can cause an
 object to
 start moving,
 stop moving
 or change
 direction.
Definition of a Force
   A Force is a push
    or a pull
Balanced Force

   A force that
    produces no
    change in an
    object’s motion
    because it is
    balanced by an
    equal, opposite
    force.
Unbalanced Forces
Are forces
 that results
 in an object’s
 motion being     +
 changed.
 Friction



A force that acts in a direction
 opposite to the motion of two
 surfaces in contact with
 each other.
 Friction
Friction causes an
 object to slow
 down and stop.
Since the amount
 of energy stays
 constant, the
 energy becomes
 heat.
Newton’s 1st Law of Motion

 Object   in
 motion
 stays in
 motion
Newton’s 1st Law of Motion

And
 Objects at
 rest stay
 at rest
Newton’s 1st Law of Motion

      they are acted upon by
 Until
 unbalanced forces.
     Inertia

   Tendency for an
    object to stay at
    rest or moving in
    a straight line at a
    constant speed.
   The mass (m
    measured in kg)
    of an object
    determines its
    inertia
Unit of Force –
Use the chart

 Unit of mass is kg
 Unit of Acceleration is m/s/s

 1 kg x 1 m/s/s = 1 kg x m/s/s
  = 1 Newton (N)
 Resulting in Force unit called
  a Newton (N)
 Newton’s 2nd
 Law of Motion
Force = Mass X
 Acceleration
F=ma
Weight (pull of gravity) is a
commonly measured force,
 calculated by F=mg, g is the
 acceleration due to gravity 9.8
 m/s2
Same floor = same friction
Same room = same air
Same car = same mass
 Newton’s 2nd Law of Motion

The greater the
 mass of an
 object, the
 greater the
 force required
 to change its
 motion.
  Newton’s 2nd Law of Motion


 Thegreater the
 acceleration of
 an object, the
 greater the force
 required to
 change its
 motion.
Your Turn!

8 How much force is needed to
  accelerate a 1,300 kg car at a rate
  of 1.5 m/s2?
F 867 N        F = m a or
G 1,950 N
                  = 1300Kg x 1.5m/s2
H 8,493 N
               F = 1950 N
J 16,562 N
  Newton’s 3rd Law of Motion
 Forevery
 action force
 there is an
 equal and
 opposite
 reaction
 force.
   Newton’s 3rd Law of Motion

All forces come
 in action-
 reaction pairs
Ex: feet push
 backward on
 floor, the floor
 pushes forward on
 feet
Newton’s 3rd Law of Motion
Rocket and Jets-
walls of the fuel
compartment
push backward on
igniting gases,
gases push
forward on the
fuel compartment
(and the rocket)
so it rises.
    Newton’s 3rd Law of Motion
   Rowing a
    boat
 Name    the Action
    Reaction pair of
    forces?

Action: Oar pushes water back.
Reaction: water pushes boat forward.
  Newton’s 3rd Law of Motion

 Bird   flying
 Name the Equal
 but Opposite
 Action--Reaction
 Forces?
Action: Wing pushes air down.
Reaction: Air pushes up on wing,
lifting bird.
    Machines do Work
 Work: the product of force
  times distance
W=Fxd
The work done by forces on an
  object = changes in energy
  for that object.
work and energy are
  measured in Joules
1 Joule=1 Newton • meter
Why use a machine?
   In an ideal
    (perfect)
    machine the
    work put into
    the machine
    (Win) = the
    work put out by
    that machine
    (Wout)
    Machines make work easier
   The ideal mechanical
    advantage of a machine (IMA)
    of a machine is the number
    of times the output force is
    larger than the input force
    IMA=Fout/Fin
   A machine can only make this
    happen by moving the input
    force through a farther
    distance than the output force
   Fin • din=Fout • dout
     Real Machines use Energy
   No real machine is
    100 % efficient. i.e.
    none put out more
    work than is put in
   Efficiency of a
    machine is work
    output/work input X
    100 %
   Eff = Wout X 100%
         W
             in
Machines use power
        Power:  the rate at
         which energy is used
         (work is done)
        P=Work/time

        Power is measured
         in H.P. or watts
        1 watt = 1 Joule
                   1 sec
  6 Types of simple machines
 Some   Simple
  Machines:
 Inclined planes

 Screws

 Pulleys

 Wheel and axle

 Levers

 Wedge
Universal Law of Gravitation

       All objects in
        the universe
        attract each
        other by the
        force of
        gravity
  Universal Law of Gravitation
     1) the mass of the object
     doing the pulling, and

Gravity varies depending
 on two factors:

    2) the distance from the center
    of that object
  On Earth gravity = 9.8 m/s/s

 Forevery
 second that an
 object falls its
 speed
 increases by
 9.8 m/s
   Universal Law of Gravitation
The acceleration
 due to gravity
 may be affected
 by the air
 resistance of the
 falling object.
 Weight= Mass (m) X
 acceleration due to gravity (g)

 Weight   Unit of mass =
  kg
 Unit of acceleration =
  m/s/s
 Unit of weight =
  Newton
 1 Newton= about ¼
  pound_
52 Objects of the same mass but of
different sizes and shapes were dropped
from a given height. Their rates of free fall
were measured and recorded. Which of the
following is most likely the question this
experiment was designed to answer?
F How does height affect the force of
gravity?
G How does gravity affect objects of
different densities?
H How do mass and weight affect falling
objects?
J How do size and shape affect an object’s
rate of free fall?
The End…

of TAKs Physics as we know it.

Now its your turn. Take the quiz on
 the overhead. Be sure to write
 down your answers. You must turn
 them in to get your coupon.