Download Energy

Energy
Energy is the ability to do work.
→ transferred from one object to another whenever work is done
→ comes in many forms that are interchangeable
→ can be stored and used at a later date
→ always conserved in a closed system
While total energy remains the same, it is not all available for our use. Heat energy which is
widely dispersed is considered waste energy. There are many kinds of energy:
Rest mass energy: total energy an object has because of its mass
E = mc2
Einstein predicted that mass can be converted to energy & vice versa. The energy produced
in a nuclear-fission power plant is an example of rest mass energy being converted into
thermal energy.
Ex: How much energy is released if 1.0 g of matter is completely converted into energy?
Nuclear energy: stored in the nucleus of an atom
This form of energy can be released in a number of ways:
→ spontaneously in the form of radioactivity
→ during nuclear fission (when a large nucleus breaks apart)
→ during nuclear fusion (when nuclei join together)
In a nuclear fission reaction, the difference in mass between the reactants and products is
called the mass defect.
Ex: When one nucleus of uranium undergoes nuclear fission, the total mass of the reactants
is 3.918472839 × 10-25 kg while the total mass of the products is 3.915360617 × 10 -25 kg.
Calculate the mass defect and the amount of energy released by this nuclear reaction.
There are about 1024 nuclei in 1 kg of uranium. Using the calculation above, what is the total
energy produced by 1 kg of uranium?
*Gravitational potential energy: result of the object's distance above a celestial body such
as Earth (We will take a closer look in the next section.)
Elastic energy: stored in an object when it is forced out of its normal shape
→ stretched bow, compressed string, flexed diving board, inflated balloon, ...
*Kinetic energy: energy of motion (We will take a closer look in the next section.)
Chemical energy: potential energy stored in molecules
→ when our digestive system breaks down food, energy is released and used to maintain
body temperature, exercise, etc
Sound energy: carried from molecule to molecule by longitudinal vibrations
→ sound travels from one place to another without the air molecules moving along with it
Thermal energy: result of the random motion of the object's molecules
Radiant energy: travels as electromagnetic waves
→ visible light, ultraviolet, infrared, radio waves
Electrical energy: associated with moving electric charge
→ lightning, current electricity
Unfortunately, more energy is always consumed than the useful work accomplished. Friction
is always present and the energy used to overcome friction becomes waste heat.
Energy is commonly measured in joules (or kilowatt hours in the case of electrical energy).
→ two golf balls raised to chest height have a gravitational potential energy of about 1 joule
→ three Olympic athletes racing at top speed have a combined kinetic energy of about
1 megajoule (1 MJ = 106 J)
→ a 5 cm wedge of apple pie has a chemical energy of about 1 MJ
→ a garbage can full of oil produces about 1 gigajoule of thermal energy when burned
(1 GJ = 109 J)
→ a TV running for 3 hours uses about 1 kW∙h of electrical energy
Assigned questions: #5 - 7