# Newton Laws

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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.

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
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
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
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.

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