WORK and ENERGY

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The Definition of Energy Energy is the ability to
conduct work. The unit of energy in SI is joule
(J). The other unit for energy is calorie (cal).
The relation between joule and calories is as
follows. 1 calorie 4.2 joule or 1 joule
0.24 calorie
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• Forms of Energy
• Heat energy
• Electric energy
• Sound energy
• Light energy
• Nuclear energy
• The use of energy in daily life
• Solar energy
• Geothermal Energy
• Wind energy
• Tidal energy
• Water energy
• Nuclear energy

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ENERGY resource

• Non renewable
• Oil (petroleum)
• Natural gas
• Coal
• Uranium (nuclear)

• Renewable
• Solar
• Wind
• Geothermal
• Biomass
• Hydro
• Ocean

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The form of energy exchange

• Energy can be transformed into many forms, such
  as
• Light to heat
• Electric to light
• Electric to heat
• Electric to sound
• Chemical to electric

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The form of energy exchange

• Energy can be transformed into many forms, but
  the amount of energy is constant. There is no
  increasing or decreasing.
• Only the form of energy has changed, not its
  amount.

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KINETIC Energy

• Kinetic energy is the energy in the form of
  movement, such as
• The running children
• The rock fall
• The running car

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Compare the picture bellow
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Compare the picture bellow
m
m1
m2
m
m2 bigger than m1
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Variable that have

• Kinetic energy depend on the mass and velocity of
  the moving object
• The larger the mass, the larger its kinetic
  energy
• The thing move faster, its kinetic energy become
  larger

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Formula of kinetic energy

• We can write formula kinetic energy
• KE ½ m v2
• KE kinetic energy (joule)
• m mass of moving object (kg)
• V velocity of moving object (m/s)

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Unit of kinetic energy

• Unit of kinetic energy in SI system is
• Joule
• Kg m2/s2
• N.m
• Watt. Second
• Another unit is
• Kalori 1 Kalori 4.2 joule

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Example

• A car have mass 50 kg, it move10 m/s. Calculate a
  mount of kinetic energy!

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POTENTIAL Energy

• Its amount depend on
• its the position or condition of the object
• If its position so higher, its potential energy
  is greater
• Its mass
• The higher its mass, its potential energy is
  greater

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Formula of gravitational potential energy

• We can write formula gravitational potential
  energy
• PE m g h
• PE gravitational potential energy (joule)
• m mass of object (kg)
• h high (m)

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Unit of potential energy

• Unit of potential energy in SI system is
• Joule
• Kg m2/s2
• N.m
• Watt. Second
• Another unit is
• Kalori

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Energy Transformation on a Roller Coaster
Example
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How High Will It Go?
Example
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• Exercise
• If the acceleration due to gravity in a certain
  place is 10 m/s2, then calculate the potential
  energy of a body, which mass is
• a. 4 kg at the height of 25 m above the ground
• b. 1.5 x 10-5 gram at the height of 6 x 106 cm
• 2. Calculate the kinetic energy owned by
• a. car of 2500 kg which moves velocity of 72
  km/hour
• b. a ball 80 gram which moves with velocity of
  15 m/s
• 3. A car is pushed by 3 people. They are Iman
  with pushing force of 300 N, Ferry of 500 N, and
  Dias with pushing force of 600 N. The car moves
  as far as 200 m from the initial place.
• a. What is work of each people ?
• b. What is total force that moves the car ?
• c. What is total work of the three people ?

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Example

• What is the potential energy if the rock that
  have mass 2 kg stay on the table that have high
  1.5 m.
• The water have potential energy 36,000 joule,
  stay on the mountain that have high 500 m,
  calculate amount of water.

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Conservation of Energy

• Look at the picture

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Conservation of Energy

• See in the picture
• When its goes down, its potential energy change
  to kinetic energy
• At the slowest point, its kinetic energy is
  greatest and potential energy is smallest.
• When it goes up, the kinetic energy changes to
  potential energy.
• At the highest point, its potential energy is
  greatest

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Conservation of Energy

• From example
• The potential energy is changed from kinetic
  energy continuously.
• Potential and kinetic energy together in form
  mechanical energy.
• It is a sum of potential and kinetic energy in a
  system

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Conservation of Energy

• Formula of mechanical energy
• Em Ek Ep
• Em mechanical energy
• Ep Potential energy
• Ek kinetic energy

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Conservation of Energy

• Energy can be transformed in one form to another,
  but its total energy is constant. In other word,
  energy is conserved.
• That is called the law of energy conservation
• Em1 Em2 Em3 Constant

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Conservation of Energy
Highest point Mechanical energy is in the form
of potential energy
lowest point Mechanical energy is in the form of
kinetic energy.
h ground
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Conservation of Energy
Em Ep
Em Ep Ek
Em Ek
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Conservation of Energy
Em Ep
Em Ep Ek
Em Ek
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Questions

• Calculate the K.E of
• a. 1 kg trolley traveling at 2 m/s
• b. 2 g bullet traveling at 400 m/s
• 2. What is the velocity of an object of mass 1 kg
  has 200 j of K.E ?

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WORK and ENERGY

• Lever
• Pulley
• Ramp (incline plane)
• Gear

Work W F x d
Simple machines
Helped by
examples
Mathematically formula

• Solar energy
• Electric energy
• Nuclear energy
• Geothermal energy
• Mechanic energy

ENERGY
The law of Conservation Of energy
fulfill
needs
examples
WORK
Gravitational Potential energy PE m.g.h
Conservation of mechanical Energy EMinitial
EMfinal
Consists of
Kinetic energy KE ½ m.v2
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• Exercise
• What is the work needed to push the table with
  force of 50 N as far as 2 m ?
• How much work you must do to lift an object with
  a mass of 1.5 kg for 2 m high if the
  gravitational acceleration in that place is 10
  m/s2 ?
• A car moves as far as 0.5 km with work 3,750
  joule. What is the magnitude force of the car ?
• A body is placed 10 m high from the ground and
  has a mass of 10 kg. If the acceleration due to
  gravity is 9.8 m/s2, what is the potential energy
  that body has ?
• A car with a mass of 800 kg moves with velocity
  of 10 m/s. what is the kinetic energy of the car
  ?

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Home Work

• A car of mass 1200 kg is moving a constants speed
  of 72 km/h
• a. find the speed of car in m/s
• b. calculate the kinetic energy of car ?
• 2. A bullet of mass 20 g leaves a gun with
  kinetic energy of 10 kJ. Calculate the speed of
  bullet ?