1. 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

2. 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 J?
h= GPE/(mg)
GPE=240.2 J
m= 7.26 kg
g= 9.81 m/s2
h=?
h= J/ [(7.26 kg)(9.81 m/s2)]
h= 3.37 m

3. 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)= kg
v= 625 m/s
KE= ½( kg)(625 m/s)2
KE= ½( kg)(390,625 m2/s2)
KE= 2832 J or 2830 J

4. 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

5. 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

6. 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

7. 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!!

8. 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

9. 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= 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

10. 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 = kg
c= 3.00 x 108 m/s2
E= ?
E= mc2
E= kg (3.00 x 108 m/s)2
E= x 1016 kg* m2/s2
E= 1.24 x 1016 J

11. 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

12. 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

13. 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……………………….

14. 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