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					TAKS Objective 5.2
Write down your answers for the next 4
questions.

   Use the formula
    chart.
   Use a calculator.
   Don’t guess!
1. The diagram represents the total travel of a
teacher on a Saturday. Which part of the trip is
made at the greatest average speed?
AQ
BR
CS
D T
2.
3. How much force is needed to
  accelerate a 1,300 kg car at a rate
  of 1.5 m/s2?
A 867 N
B 1,950 N
C 8,493 N
D 16,562 N
4. A ball moving at 30 m/s has a momentum
of 15 kg·m/s. The mass of the ball is —


A 45 kg

B 15 kg

C 2.0 kg

D 0.5 kg
Check your answers, if they are all
correct, try the quiz at the end . . .

1. C
2. A
3. B
4. D
    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
   Force = Mass x
              Acceleration
   Units of force are
    Newtons (N)
   Motion can be described simply

 Motion  is a
  change in an
  object’s position
 Average velocity
  (speed) is a
  change of the
  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)
The diagram represents the total travel of a
teacher on a Saturday. Which part of the trip is
made at the greatest average speed?
       How do we work this one?
       Calculate v = d/t for each segment.
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
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.
     Law of Inertia is another name
     for Newton’s 1st Law

   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 or
the Law of Acceleration
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!

How much force is needed to
  accelerate a 1,300 kg car at a rate
  of 1.5 m/s2?
To solve this:

       F=ma      or
          = 1300Kg x 1.5m/s2
       F = 1950 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.
    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
    Machines make work easier
   The ideal mechanical
    advantage of a machine (IMA)
    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 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
 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_
Last quiz!
   For the next 7 slides, write the
    answers on your own paper. Label
    this one Obj. 5.2
   If you have time, check out TAKS
    Dr. Try to answer each question,
    and then see the answer and why it
    is correct. This is the practice test
    you took in September.
   GOOD LUCK!
1. The frog leaps from its resting position at the
lake’s bank onto a lily pad. If the frog has a
mass of 0.5 kg and the acceleration of the leap
is 3 m/s2, what is the force the frog exerts on
the lake’s bank when leaping?




         A 0.2 N           B 0.8 N
         C 1.5 N           D 6.0 N
2. If a force of 100 newtons was
exerted on an object and no work
was done, the object must have —


    A accelerated rapidly
    B remained motionless
    C decreased its velocity
    D gained momentum
3. How much work is performed when a 50 kg
  crate is pushed 15 m with a force of 20 N?
A 300 J
B 750 J
C 1,000 J
D 15,000 J
4.
5.
 6. Which lever arrangement requires
 the least effort force to raise a 500 N
 resistance?

A.                    C.




B.                     D.
7. The illustration below shows a student
standing on a skateboard about to throw a ball.
Which picture correctly shows the movement of
the skateboard after the release of the ball?
The End…Check your answers . . .
1. C 2. B 3. A 4. C 5. A 6. A 7. D

Turn in your answers with your name
 and your teacher’s name on it.
Now its your turn. Work through
 problems in the workbooks, ask for
 help if you need to from any science
 teacher, and attend the tutorials for
 objectives on which you did not
 score 100%.

				
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