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

Forms of Energy a.Heat energy b.Electric energy c.Sound energy d.Light energy e.Nuclear energy The use of energy in daily life a.Solar energy b.Geothermal Energy c.Wind energy d. Tidal energy e.Water energy f. Nuclear energy

 Non renewable › Oil (petroleum) Oil (petroleum) › Natural gas Natural gas › Coal Coal › Uranium (nuclear) Uranium (nuclear)  Renewable › Solar Solar › Wind Wind › Geothermal Geotherma › Biomass Biomass › Hydro Hydro › Ocean

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

 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.

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

m1m1 m m2m2 m m 2 bigger than m 1

 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

 We can write formula kinetic energy KE = ½ m v 2 › KE = kinetic energy (joule) › m= mass of moving object (kg) › V = velocity of moving object (m/s)

 Unit of kinetic energy in SI system is: › Joule › Kg m 2 /s 2 › N.m › Watt. Second  Another unit is: › Kalori 1 Kalori = 4.2 joule

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

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

 Unit of potential energy in SI system is: › Joule › Kg m 2 /s 2 › N.m › Watt. Second  Another unit is: › Kalori

Example

Exercise : 1.If the acceleration due to gravity in a certain place is 10 m/s 2, 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 gram at the height of 6 x 10 6 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 ?

 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.

 Look at the picture

 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

 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

 Formula of mechanical energy E m = E k + E p  E m = mechanical energy  E p = Potential energy  E k = kinetic 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

h ground Highest point Mechanical energy is in the form of potential energy lowest point Mechanical energy is in the form of kinetic energy.

Em = Ep Em = Ep + Ek Em = + Ek

Em = Ep Em = Ep + Ek Em = + Ek

1. 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 ?

Work W = F x d Gravitational Potential energy PE = m.g.h Conservation of mechanical Energy EM initial = EM final The law of Conservation Of energy Lever Pulley Ramp (incline plane) Gear Simple machines Solar energy Electric energy Nuclear energy Geothermal energy Mechanic energy WORK ENERGY Helped byexamples Mathematically formula fulfillneeds examples Kinetic energy KE = ½ m.v 2 Consists of WORK and ENERGY

Exercise 1.What is the work needed to push the table with force of 50 N as far as 2 m ? 2.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/s 2 ? 3.A car moves as far as 0.5 km with work 3,750 joule. What is the magnitude force of the car ? 4.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 ? 5.A car with a mass of 800 kg moves with velocity of 10 m/s. what is the kinetic energy of the car ?

1. 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 ?