Energy

ENERGY Energy- the ability to do work SI unit for energy is Joules (J) 2 basic forms Potential energy- energy of position Kinetic energy- energy of motion Energy is classified by its source Mechanical potential energy Common example is gravitational potential energy

Energy Gravitational potential energy GPE= mgh EX. How high has a 7.26 kg shot put been thrown if it has a potential energy of 240.2 J? h= GPE/(mg) GPE=240.2 J m= 7.26 kg g= 9.81 m/s2 h=? h= 240.2 J/ [(7.26 kg)(9.81 m/s2)] h= 3.37 m

Kinetic Energy Kinetic energy- energy of motion KE= ½ mv2 What is the kinetic energy of a 14.5 g rifle bullet moving at 625 m/s? KE=? m= 14.5 g (convert to kg)= 0.0145 kg v= 625 m/s KE= ½(0.0145 kg)(625 m/s)2 KE= ½(0.0145 kg)(390,625 m2/s2) KE= 2832 J or 2830 J

Chapter 6 Energy Thermal Energy- the sum of all of the kinetic energies of all the particles in an object Theoretically, At 0 Kelvin all particle movement stops, but this is not achievable on earth Acoustic Energy- involves random vibrations and motion of particles Produces sound must travel through matter-cannot exist in a vacuum Moves in periodic motion- back and forth vibrations

Energy Electrical Energy- forces acting on other electrical charges Opposite attract, like repel Natural sources- lightning, electric rays and eels Man made sources- batteries, generators, etc Magnetic Energy-ability to do work through the influence of a magnetic field Radiant Energy- also called electromagnetic energy- does not require matter through which to travel, can travel in a vacuum Most common form is visible light

Energy Chemical Energy- potential energy stored in chemical bonds During chemical reactions atoms rearrange their bonds and energy is released or absorbed Energy can be released as thermal, radiant, or acoustic energy Note: we will go over this in more detail in Chapters 18 and 19

Energy Nuclear Energy- this is the energy associated with the nucleus of an atom Can be released in 2 ways Fusion- is the combining of 2 or more nuclei to form a larger nuclei stars 2 H atoms combine to form He Fission- is the splitting apart of a nucleus into 2 more smaller nuclei Man made nuclear power plants to generate power Nuclear energy always releases radiation-DANGER REMEMBER- energy cannot be created nor destroyed only transferred- all energies in the end must equal that with which you started!!

Energy Mass Energy- this is the largest source of potential energy in the universe It is the energy equivalent to all matter itself This is where Einstein’s theory is applied E= mc2 Energy is equal to the mass times the speed of light squared

E=mc2 What is the energy equivalent of the mass of a 0.01 g plant mite, a tiny spider-like animal? (remember that c= 3.0 x 108 m/s) E=mc2 E=? m= 0.01g (you have to convert to kg, divide by 1000) m= 0.00001 kg or 1.0 x 10-5 kg c= 3.0 x 108 m/s E= 1.0 x 10-5 kg (3.0 x 108 m/s)2 E= 1.0 x 10-5 kg (9.0 x 1016 m2/s2) E= 9.0 x 1011 kg m2/s2 E= 9.0 x 1011 J

Example 6-3 How much mass energy, in joules, could be obtained from the complete conversion of a compact 138 g media player? m= 138 g = 0.138 kg c= 3.00 x 108 m/s2 E= ? E= mc2 E= 0.138 kg (3.00 x 108 m/s)2 E= 1.242 x 1016 kg* m2/s2 E= 1.24 x 1016 J

Energy Conservation 1st Law of Thermodynamics- conservation of energy energy cannot be created nor destroyed only transferred, therefore the energy before the transformation must equal the energy after Sometimes when energy is transferred some energy is ‘lost’ to the surrounding, Because of this we measure the efficiency This a comparison of the measurement of the amount of usable energy produced with the amount available before the transformation

Energy Conservation Energy can be transferred to one or more forms of energy Chemical energy from food becomes thermal energy in our cells and mechanical energy in our muscles The 1st Law of thermodynamics is easily demonstrated by a pendulum Consists of a heavy weight at the end of an arm that swings back and forth on a pivot point at its upper end

Collisions and Energy As we have discussed before momentum and kinetic energy are properties of motion Momentum is a vector defining a system’s quantity of motion Kinetic energy is a scalar quantity describing the mechanical energy of a moving system Collisions……………………….

Collisons There are 3 types of collisions 1. Elastic collisions- occurs when 2 objects collide and bounce (rebound) off from one another The sum of their momentums and the sum of their kinetic energies are the same before and after the collision 2. Partially elastic collisions – occurs when one or both objects in a collision are deformed before rebounding 3. Inelastic collision- occurs when two objects collide and stick together REMEMBER ENERGY IS NOT LOST BUT TRANSFERRED