The Nature of EnergyWhat is energy?Energy is the ability tocause a change or Mechanicalthe ability to do work Electrical Energy EnergyWhat Solar Energy are the differentforms of energy? Heat Energy Nuclear Energy
The energy of different objects may fall intotwo main categories:Kinetic Energy and Potential EnergyKinetic Energy is the energy of a movingobjectPotential Energy is stored energy. Thiscan be thought of in two ways. Storedenergy in our bodies or in a battery is calledchemical potential energy. Stored energy energydue to the position of an object above thesurface of the earth is gravitationalpotential energy.
Calculating Kinetic EnergyKinetic Energy depends upon two factors: the mass ofthe object and its velocity.Mass is measured in kg and velocity is measured in m/sWhen the units are multiplied, the result is kg m2/s2Since a Newton (N) is a kg m/s2, therefore kg m2/s2 isthe same as a N-m, which is the same as a joule (J).Hence, the unit of kinetic energy is the joule.
Practice ProblemsHow much energy does a soccer player with amass of 75 kg and a velocity of 5.5 m/s possess?KE = ½mv2 KE = ½(75 kg)(5.5 m/s)2KE = 1.1 X 103 kgm2/s2 1 kgm/s2 = 1NKE = 1.1 X 103 Nm 1 Nm = 1 Joule (J) KE = 1.1 X 103 Joules (J)
Solve the following:What is the velocity of a car with a mass of 675kg and a kinetic energy of 1690 joules?2(KE)=2( ) 2KE = mv ½mv 2 2 2KE = v2 m 2KE = v v= 2(1690J) m 675 kg v = 2.24 m/s
Calculating Gravitational Potential EnergyGravitational Potential Energy (GPE) depends uponthree factors: the mass of the object, the height of theobject from the surface of the earth, and the gravitationalacceleration constant (on earth = 9.8 m/s2)Notice how the units multiply :mass (kg) x m/s2 x height (m). Hence the unit is kg m2/s2which is the joule (J).Let’s do a practice problem…
Potential EnergyCalculate the energy possessed by a rock onthe side of a cliff. The rock has a mass of 237kg at an elevation of 45 meters.PE = mgh PE = (237 kg)(9.8 m/s2)(45m)PE = 1.0 X 105 kgm2/s2PE = 1.0 X 105 NmPE = 1.0 X 105 Joules
What is the Law of Conservation of Energy? EnergyEnergy cannot be created nor destroyed….but….Energy can be transformed from one type toanother. In this diagram, electrical energy is converted into thermal (heat) energy and light energy.
There are many energy transformations in anautomobile.The explosion of the gasoline involves therelease of chemical energy.The chemical energy causes the pistons inthe engine to move (mechanical energy)The moving pistons affect many moving partsincluding a generator which produceselectrical energy which keeps the batterycharged.The moving pistons and other moving partsalso produce heat energy.
Objects can convert potential energy to kineticenergy or kinetic energy to potential energy.The diagram below illustrates this relationship.
In nuclear reactions some mass is converted intoenergy.
The major source of energy is the SUN.In photosynthesis plants convert sunlight intostored energy in the plants.Animals and humans eat the plants to getenergy.The human body “burns” this stored energy inunits called Calories.One Calorie is equal to 4.18 J.The human body stores energy in Calories andwill utilize “burn” this energy as needed.
Particles of matter are in constant motion. Thismotion relates directly to the state of matter of theobject (solids, liquids, or gases).Temperature affects how fast these particlesmove. The higher the temperature the faster theparticles move. Moving particles possess kineticenergy.Temperature is defined at the average kineticenergy of the particles of an object.
Thermal Energy is the sum total of all of theenergy of the particles of an object.Thermal energy and temperature are relatedthough DIFFERENT.Temperature is the average kinetic energy of theparticles of an object.Thermal energy is the total amount of energy ofthe particles of an object.A bathtub full of water at 100oF has more thermalenergy than a thimble of water at 100oF. Thetemperature is the same but the total amount ofenergy is different. The bathtub has more energy.
What is heat? heatHeat is thermal energy that flows fromsomething at a higher temperature tosomething at a lower temperature.What is specific heat? heatSpecific heat is a property of matter whichdetermines how readily a material is to absorbheat and change temperature.Specific Heat is defined as the amount of heatenergy needed to raise the temperature of 1kg of a substance by 1 oC or 1 K.
Did you notice that water has a very high specificheat, whereas iron has a low specific heat?Water requires a lot of heat energy to raise itstemperature.
Metals require little energy to raise itstemperature.Thermal energy can be calculated using thefollowing formula:
Try this one!! Answer = 376 J/kg K Did you do this problem?
Transferring Thermal EnergyHow is Thermal Energy Transferred? YOU MUSTKNOW THIS!!!!!Conduction – direct contactConvection – through a fluidRadiation – by electromagnetic waves
What is heat transfer by conduction? conductionHeat transfers as particles of an object increasetheir collisions as heated. These collisionstransfer the heat energy through the object bycolliding with adjacent particles.
What is heat transfer by convection? convectionHeat is transferred through a substance throughcurrents. This occurs in fluids (liquids ANDgases)Convection currents are caused by heating of aliquid or gas, the liquid or gas rises, then coolsand falls. This occurs in the mantle of the earthAnd in the atmosphere.Most of our weather patterns are the result ofconvection currents in the atmosphere.
What is heat transfer by radiation?Radiation is heat transfer by electromagneticwaves. These wave may pass through all statesof matter and also through NO matter – such asthe vacuum of space.This energy is often called radiant energy.Radiant energy from the sun travels through thevacuum of until it reaches the earth.
How is heat flow controlled?Insulators – a material which does not allow heatto pass through it easily. Some animals have good insulation to survive severe winters.
Buildings and houses are insulated so that heatdoes not pass out of (winter time) and into(summer time).
Using heat – How do we use heat in our lives?Forced-Air Systems – a fuel is burned in afurnace and a fan circulates the heat in the house
Radiator Systems – closed metal containers thatcontain hot water or steam. The thermal heat istransferred to the air and circulated by convectioncurrents.Electric radiators – heat metal coils whichtransfer the thermal heat to the surrounding air.
Automobile engines are usually four-strokeengines since each four-stroke cycle convertschemical/thermal energy to mechanical energy.
Refrigerators, air conditioners, and heat pumps –how do they work?A coolant is circulated through pipes by acompressor. When the pipes get small andnarrow the coolant compresses and changes to aliquid giving off heat energy. When the pipes getlarger, the coolant changes from a liquid to a gas(evaporates) causing the area to absorb heat andget cooler
The human coolant - In-built cooling systemThe human body has a cooling system whichfunction automatically – perspiration – sweat. Like a refrigeration system, the evaporation of the sweat from the surface of the body causes energy to be absorbed from the skin, causing the skin to feel cooler. No sweat!!!
Thank youEfforts by:-ESHA DHIRXII-SCIENCE (2011-12)FAITH ACADEMY
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