TAKS Objective 5

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TAKS Objective 5

• Motion , Forces
• and Energy

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Energy

• Is defined as the Ability to do Work
• Energy has Two
• Types

Kinetic (Energy of Motion) and Potential (Stored
Energy)
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Kinetic Energy

• KE ½ m v 2
• Ex A moving car has the ability to
• do work on the light pole if it hits it.

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Gravitational Potential Energy or Will it fall?

• GPE m g h
• m is the mass of the
• object in Kg,
• g is the acceleration
• due to gravity which is
• 9.8 m/s2 on earth and
• h is the height in meters

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Use the formula page! PE mgh

• 41 What is the potential energy of the rock?
• A 59,900 joules
• B 64,600 joules
• C 93,100 joules
• D 121,600 joules

m 95 kg g 9.8 m/s2 h 100 m 95 kg x
9.8 m/s2 x 100 93,100 joules C
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Electrical Energy - Moving electrons in a path
is electricity

• Electrical Potential Difference (v) is measured
  in Volts
• The rate of moving electric charges, Electric
  Current (I), is measured in Amperes
• Resistance or opposition to the movement of the
  energy is called Resistance (R).

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Circuits 2 types

• Series circuits are the most simple.
• One (1) path for the current to travel.
• Contains an energy source, a path, and a load
  (something for it to do, like a lamp)

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Circuits 2 types

• Parallel circuits provide more than one path for
  the current to travel.
• Most circuits are parallel, since if one lamp
  goes out, the others can stay lit.

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• Which switches, if opened, will
• cause the light bulb to stop glowing?

• Q
• R
• H. S
• J. T

It is the only switch in series to both the
battery and light.
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USE THE FORMULA SHEET!!

• What is the current in a copper wire that has a
  resistance of 2 ohms and is connected to a 9 volt
  electrical source?
• A. 0.22 amp
• B. 4.5 amps
• C. 11.0 amps
• D. 18.0 amps

V I R so, 9V I x 2 ohms or 4.5 amps
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Heat- Transfer of Thermal Energy
Three forms of heating

• 1. Conduction-direct contact, a pot heating on a
  stove (solids)
• 2. Convection- heating by circulating fluids,
  (gas and liquid) heating from a fireplace
• And. . .

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3. Radiation Transfer of Electromagnetic (E.M.)
Energy

• Objects are heated when exposed to infrared
  radiation
• The suns heats the earth by sending infrared
  radiation along with other forms of E.M. energy
  3.0 x 108 meters through empty space

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Heat moves by conduction in solids since the
particles are close together and vibrate. . .

• 43 Heat convection occurs in gases and liquids.
  Heat convection does not occur in solids because
  solids are unable to
• A absorb heat by vibrating
• B transfer heat by fluid motion
• C emit radiation by reflecting light
• D exchange heat by direct contact

Solids do radiate heat to their surroundings
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2 The primary way liquids and gases transmit heat
is by the process of

• F reflection
• G conduction
• H radiation
• J convection

Fluid heat movement is convection. Fluid motion
occurs in liquids and gases.
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50 A solar heater uses energy from the sun to
heat water. The heaters panel is painted black
to
Convection is movement of heat in fluid matter,
heat loss would be from a solid exterior Not G

• F improve emission of infrared radiation
• G reduce the heat loss by convection currents
• H improve absorption of infrared radiation
• J reduce the heaters conducting properties

Painting a substance will not change its
conductivity That is a property of metals. It
would have to be made of a different substance to
change that Not J
Emission is giving off we want to absorb Not F
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Waves - Energy carried by rhythmic disturbances

• Two types
• 1. E.M. radiation move through empty space
• 2. Mechanical require a medium (air, water or any
  type of matter) for movement

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Waves - 2 Types
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All waves have similar properties

• Frequency- the number of vibrations per second or
  the speed of the movement of the vibrating
  particles
• Amplitude the size of the movement of the
  vibrating particles
• Both are controlled by the disturbance that
  created the waves

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Velocity of all waves - vf ?

• f-frequency and ? is wavelength (distance between
  identical points on two consecutive waves)
• Reflection- bounce off barriers in regular ways
• Refraction- waves can change direction when speed
  changes

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And the answer is?
J 3300 Hz

• 38 At 0C sound travels through air at a speed of
  330 m/s. If a sound wave is produced with a
  wavelength of 0.10 m, what is the waves
  frequency?
• F 0.0033 Hz
• G 33 Hz
• H 330 Hz
• J 3300 Hz

Use the formula chart!!! Velocity f ? OR 330
m/s f x 0.10 m
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Sound Waves move through matter not through empty
space.

• 32 One tuning fork is struck and placed next to
  an identical fork. The two forks do not touch.
  The second tuning fork starts to vibrate because
  of
• F interference
• G the Doppler effect
• H resonance
• J standing waves

Resonance is the vibration of another object
struck by a wave of the correct frequency. Since
the forks are identical, the second one receives
the correct frequency to begin vibrating.
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Forces and Motion

• Forces can create changes in motion
  (acceleration)
• Deceleration is negative acceleration

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Velocity Graphs V distance time

• Velocity (v) is the slope (rise over run) of a
  position (d) vs. time (t) graph

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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? F Q G R H S J
T
How do we work this one? Calculate v d/t for
each segment.
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Acceleration Graphs

• Acceleration (a) is the slope of a velocity (v)
  vs. time (t) graph
• Plotted on a distance vs. time graph,
  acceleration is an exponential curve

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Acceleration is a change in an objects velocity
(speed or direction)

• When an objects speed changes over time it is
  accelerating (or decelerating)
• A vfinal vinitial
• time
• Units for acceleration m/s/s or m/s2

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Definition of a Force

• A Force is a push or a pull

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Balanced Force

• A force that produces no change in an objects
  motion because it is balanced by an equal,
  opposite force.

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4 The picture shows the position of a ball every
0.25 second on a photogram. Using a ruler,
determine the velocity of the ball.

• F 3.5 cm/s
• G 10.5 cm/s
• H 14.0 cm/s
• J 28.0 cm/s

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Use the ruler on the side of the chart and the
equation for velocity. The answer was H.
Measure from the center of ball 1 to the center
of ball 2 and divide by .25.
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Unbalanced Forces

• Are forces that results in an objects motion
  being changed.

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Friction

• A force that acts in a direction opposite to the
  motion of two surfaces in contact with each other.

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Friction

• Friction causes an object to slow down and stop.
• Since the amount of energy stays constant, the
  energy becomes heat.

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Newtons 1st Law of Motion

• Object in motion stays in motion

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Newtons 1st Law of Motion

• And Objects at rest stay at rest

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Newtons 1st Law of Motion

• Until they are acted upon by unbalanced forces.

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Inertia or Newtons 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

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Newtons 2nd Law of Motion

• Force Mass X Acceleration
• Fma
• Weight (pull of gravity) is a
• commonly measured force, calculated by Fmg, g
  is the acceleration due to gravity 9.8 m/s2

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Newtons 2nd Law of Motion

• The greater the mass of an object, the greater
  the force required to change its motion.

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Newtons 2nd Law of Motion

• The greater the acceleration of an object, the
  greater the force required to change its motion.

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11 The frog leaps from its resting position at
the lakes 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 lakes bank when leaping?

• A 0.2 N
• B 0.8 N
• C 1.5 N
• D 6.0 N

Formula chart says Fma, m is mass in kg, a is
acceleration in m/s2. So, .5 kg x 3 m/s2 1.5 N
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Newtons 3rd Law of Motion

• For every action force there is an equal and
  opposite reaction force.

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Newtons 3rd Law of Motion

• All forces come in action-reaction pairs
• Ex feet push backward on floor, the floor pushes
  forward on feet

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27 A ball moving at 30 m/s has a momentum of 15
kgm/s. The mass of the ball is

• A 45 kg
• B 15 kg
• C 2.0 kg
• D 0.5 kg

Formula Page says that Momentum Mass x Velocity
So 15 kg.m/s M x 30 m/s solving for M it
is
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Work

• Work using a force
• for a distance
• W F x d
• The work done by forces on an object changes in
  energy for that object.
• Work and Energy are measured in Joules
• 1 Joule1 Newton meter

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• 42 How much work is performed when a 50 kg crate
  is pushed 15 m with a force of 20 N?
• F 300 J
• G 750 J
• H 1,000 J
• J 15,000 J

Use the formula Work Force x distance Force
of 20 N x 15 meters 300 Joules Answer
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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 IMAFout/Fin
• A machine can only make this happen by moving the
  input force through a farther distance than the
  output force
• Fin dinFout dout

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• 48 The diagram shows an electric motor lifting a
  6 N block a distance of 3 m. The total amount of
  electrical energy used by the motor is 30 J. How
  much energy does the motor convert to heat?
• F 9 J
• G 12 J
• H 18 J
• J 21 J

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Work Input 30J done by the motor
Work Output Resistance Force x Resistance
Distance Workout 18J 6N x 3m
The difference is lost as heat due to friction,
which is 30J 18J 12J Answer G
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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
• Win

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Machines use power

• Power the rate at which energy is used (work is
  done)
• PWork/time
• Power is measured in H.P. or watts
• 1 watt 1 Joule
• 1 sec

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45 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

Work Force x Distance Work 0 Force 100
N so 0 J 100 N x d distance must be 0 It
did not move!
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Universal Law of Gravitation

• All objects in the universe attract each other by
  the force of gravity

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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
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On Earth gravity 9.8 m/s/s

• For every second that an object falls its speed
  increases by 9.8 m/s

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Weight Mass (m) X gravity (g)

• Weight Unit of mass kg
• Unit of acceleration m/s/s
• Unit of weight Newton
• 1 Newton about ¼ pound