PPT ON WORK AND ENERGY BYG.MOTHY K.V.NO.1 UPPAL

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IT IS A PPT ON WORK AND ENERGY

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WORK AND ENERGY

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CONTENT WORK ENERGY FORMS OF ENERGY KINETIC ENERGY POTENTIAL ENERGY POTENTIAL ENERGY OF AN OBJECT AT A HEIGHT ENERGY CONVERSION LAW OF CONSERVATION F ENERGY RATE OF DOING WORK

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Work Work is said to be done when a force acts on an object and the object is displaced in the direction of force. The work done on an object is the product of the force applied and the displacement. Work done = force x displacement W = F X s The unit of work is joule (J).

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If F is 1 Newton and displacement is 1 metre then the work done is 1Nm or 1 joule (J). So 1 joule is the amount of work done when a force of I Newton displaces an object by 1 metre. Eg :- If a force of 5 N acts on an object is displaced through 2 m in the direction of force, then work done is 5 N x 2 m = 10 Nm or 10 J

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The work done by a force may be positive or negative. The work done by a force is positive if the force and displacement are in the same direction. The work done by a force if negative if the force and displacement are in opposite directions. The work done by a force is zero if there is no displacement. The work done by a force is zero if the force is perpendicular to the displacement. POINTS

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Eg :- When we lift an object the object moves upward in the direction of force. Here the work done is positive. But there is the force of gravity acting downward on the object. The work done by the force of gravity is negative. Eg :- A porter lifts a luggage of 15 kg from the ground and puts it on his head 1.5 m above the ground. Calculate the work done by him on the luggage. Mass of luggage m = 15 kg, displacement = 1.5 m, Acceleration due to gravity = 10 ms Work done W = F x s = mg x s = 15 kg x 10 ms x 1.5 m = 225 kg ms = 225 N m = 225 J

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Energy Energy exists in many forms. Energy can be moved from one object to another. Energy can be changed from one form to another. Energy cannot be created or destroyed.

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Energy the “stuff” that makes “stuff do stuff” OR the ability to do work. (W=F x D) (F=force d=distance)

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The energy of an object is its capacity for doing work. The unit of energy is the same as that of work that is joule(J ). 1 joule is the energy required to do 1 joule of work. 1000 J = 1 kilo joule (kJ ). EG. When a fast moving cricket ball hits a stationary wicket ,the wicket is throw away. Energy :

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Eg. When a raised hammer falls on a nail placed on a piece of wood, it drives the nail into the wood. Eg. When a car or bus starts moving

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We use energy every day. Energy is need to operate machines, to heat and cool our homes and schools, to cook, to provide light and to take people from place to place .

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THE SUN Almost all of the energy we use comes from the sun. The sun is like a giant energy factory. The easiest way to get energy from the sun is to use its light.

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James prescott joule was an outstanding british physicist. He is best known for his research in electricity and thermodynamics. Amongst other things, he formulated a law for the heating effect of electric current. He also verified experimentally the law of conservation of energy and discovered the value of the mechanical equivalent of heat. The unit of energyand work called joule, is named after him.

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Forms of Energy

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Forms of energy Mechanical Heat Chemical Electrical Electromagnetic Nuclear

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Mechanical Energy Energy of motion or position Sound, wind, waterfall, compressed spring KE or PE Not 100% efficient much lost to heat

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Heat The internal motion of an objects atoms and molecules. Measured by temperature. The faster particles move, the more thermal energy they have. KE only

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Chemical Energy Energy stored by chemical bonds in an object. When bonds are broken energy is released. PE only gasoline, food, coal, wood

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Electrical Energy Moving electrical charges. Electricity from batteries, power lines, lightning KE

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Electromagnetic Energy energy that travels in waves; have electrical and magnetic properties Light, Magnetism, X-Rays, Radio waves, microwaves, ultraviolent and infrared radiation KE

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Nuclear Energy Energy stored in center(nucleus) of an atom Fission (breaking apart) Fusion (forming) The sun Most powerful PE only

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Six Forms of Energy Mechanical Chemical Electrical Heat Light Nuclear

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Kinetic Energy The energy of motion is called kinetic energy. The faster an object moves, the more kinetic energy it has. The greater the mass of a moving object, the more kinetic energy it has. Kinetic energy depends on both mass and velocity.

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The kinetic energy possessed by an object of mass m and moving with uniform velocity v is E = mv Eg :- An object of mass 15 kg is moving with a uniform velocity of 4 ms . What is the kinetic energy possessed by the object ? Mass of the object m = 15 kg. Velocity of the object v = 4 ms E = mv = x 15 kg x 4 ms x 4 ms = 120 J The kinetic energy of the object is 120 J

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Kinetic Energy

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Kinetic Energy Energy of a moving object

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Examples of Kinetic Energy… Shooting a rubber band. Water falling over the fall. A Yo-Yo in motion. Releasing the arrow from the bow.

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The kinetic energy of an object is the energy possessed by the object due to its motion. All moving objects possess kinetic energy. A falling coconut, a speeding car, a flying aircraft, flowing water, blowing wind, a running athlete etc. possess kinetic energy. The kinetic energy of an object depends upon its speed. An object moving faster has more kinetic energy than an object moving slower.

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What is Potential Energy? Energy that is stored and waiting to be used later

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Examples of Potential Energy The energy in matter due to its position or the arrangement of its parts

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Potential Energy Potential Energy is stored energy. Stored chemically in fuel, the nucleus of atom, and in foods. Or stored because of the work done on it: Stretching a rubber band. Winding a watch. Pulling back on a bow’s arrow. Lifting a brick high in the air.

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Gravitational Potential Energy Potential energy that is dependent on height is called gravitational potential energy.

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Gravitational Potential Energy A waterfall, a suspension bridge, and a falling snowflake all have gravitational potential energy.

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Gravitational Potential Energy If you stand on a 3-meter diving board, you have 3 times the G.P.E, than you had on a 1-meter diving board.

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Energy Conversion

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Changing forms of Energy An example of transforming chemical energy is a car engine. Chemical potential energy in gasoline is transformed into kinetic energy of the car as it moves!!

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Steam Engines Transform Energy Potential energy is stored in fuel. Chemical change produces heat energy. Heat changes water to steam. Steam provides mechanical energy.

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Mechanical energy moves the ship . A moving ship has kinetic energy. Steam Engines Transform Energy

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The Steam Engine Steam turns large turbines. Turbines turn a series of gears. The gears reduce the turning speed of the shaft.

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Potential to Kinetic Potential Energy (fuel) Heat Energy (steam) Mechanical Energy (engine parts) Kinetic Energy (ship moves)

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Energy Conversion

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Kinetic-Potential Energy Conversion Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride.

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Kinetic-Potential Energy Conversions As a basketball player throws the ball into the air, various energy conversions take place.

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Figure 10:Common Energy Transformations Every day, energy transformations are all around you. Some of these transformations happen inside you!

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Energy Transformation in Juggling Any object that rises or falls experiences a change in its kinetic and gravitational potential energy. Look at the orange in Figure 11. When it moves, the orange has kinetic energy. As it rises, it slows down. Its potential energy increases as its kinetic energy decreases.

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At the highest point in its path, it stops moving. Since there is no motion, the orange no longer has kinetic energy. But it does have potential energy. As the orange falls, the energy transformation is reversed. Kinetic energy increases while potential energy decreases.

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Energy Transformation in a Pendulum In a pendulum, a continuous transformation between kinetic and potential energy takes place. At the highest point in its swing, the pendulum in Figure has no movement, so it only has gravitational potential energy. As it swings downward, it speeds up. Its potential energy is transformed to kinetic energy.

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The pendulum is at its greatest speed at the bottom of its swing. There, all its energy is kinetic energy. As the pendulum swings to the other side, its height increases. The pendulum regains gravitational potential energy and loses kinetic energy. At the top of its swing, it comes to a stop again. And so the pattern of energy transformation continues.

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Energy Transformation in a Pole Vault A pole-vaulter transforms kinetic energy to elastic potential energy, which then becomes gravitational potential energy. The pole-vaulter you see in Figure has kinetic energy as he runs forward. When the pole-vaulter plants the pole to jump, his velocity decreases and the pole bends.

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His kinetic energy is transformed to elastic potential energy in the pole. As the pole straightens out, the pole-vaulter is lifted high into the air. The elastic potential energy of the pole is transformed to the gravitational potential energy of the pole-vaulter. Once he is over the bar, the pole-vaulter ’ s gravitational potential energy is transformed back into kinetic energy as he falls toward the safety cushion.

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Law of Conservation of Energy With every transformation, some energy is converted to less useful forms. Energy conversions are not 100% efficient. The energy output for the intended purpose is seldom the same as the energy we put in. 100 J electricity in 95 J heat out 5 J light out

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The Law of Conservation of Energy The Law of Conservation of Energy states that energy cannot be created or destroyed. The big picture… the total energy in the universe remains constant.

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But how? If I stop pumping while I’m swinging, I stop!! So, where’s the energy? Example of law of conservation of energy

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Conservation of Energy You need to remember friction… As you slow down on the swing, the hooks and the chain rub against each other and air pushes against the rider.

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Friction causes some of the mechanical energy of the swing to change to thermal energy and the temperature of the hooks and chain heat up a little. The energy is still there, just in a different form!!

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Conservation of Energy Energy is conserved . Conservation of energy means it can change forms between kinetic and potential, but it never disappears.The total amount of energy is always the same.

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Conservation of Energy In both the cases Energy is transformed… not destroyed!! The total amount of energy stays the SAME!!

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Energy in Your Body Even the energy converted in your body follows the law of conservation of energy. Chemical potential energy is transferred to kinetic energy that allows your body to move!!

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Rate of doing work (Power) Power is the rate of doing work. If W is the work done in time t, then work done W Power = ---------------- or P = --- time taken t The unit of power is watt (W). 1 watt is the power of an agent which does work at the rate of 1 joule per second. 1 watt = 1 joule / second or 1 W = 1 J s 1 kilowatt = 1000 watts 1 kW = 1000 W 1 kW = 1000 J s

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Commercial unit of power The commercial unit of energy is kilowatt hour (kW h). 1 kilowatt hour is the energy used in one hour at the rate of 1 kilowatt (or 1000 J s ). 1 kW h = 1 kW x 1 h = 1000 W x 1 h = 1000 W x 3600 s = 3600000 J 1 kW h = 3.6 x 10 J The electrical energy used in homes and industries are expressed kilowatt hour. The electrical energy used during a month is expressed in ‘units’. Here 1 unit means 1 kilowatt hour. -6

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G.MOTHY (G.L) MADE BY

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THANK YOU

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