What to Study – Energy and Waves
Law Conservation of Energy: energy cannot be created or destroyed, only changed from
one form to another
Forms of Energy
1. Mechanical: energy that moves an object
- Ex: anything that moves
2. Chemical: energy stored in chemical bonds
- Ex: food, batteries, fuels, unlit match
3. Thermal: heat energy
- Energy in moving particles of matter (Faster  more thermal energy
produced)
- Result of friction
- Causes changes in temperature and phases
4. Electromagnetic:
- Transmitted in the form of electromagnetic waves
- Can travel through a vacuum
5. Nuclear: Stored in the nucleus of an atom
6. Electric: a result of moving electrons
Sources of Energy
Renewable Energy:
- Advantages:
o CO2 not released  no global warming
o S and N not released  no acid rain
- Disadvantages:
o Can be expensive.
o Habitat destruction (disrupt ecosystems)
o Possible pollution
- Examples:
1. Solar (expensive)
2. Wind (no pollution, low costs, habitat destruction, no wind  no energy)
3. Geothermal: heat from Earth’s interior (pollution)
4. Hydropower: energy from running water (habitat destruction, fish cannot
reproduce)
5. Biomass: energy from byproducts of human activity – wood, garbage, crops
(pollution, disruption of ecosystems, expensive)
Nonrenewable Energy
- Disadvantage:
o CO2 released  global warming
o S and N released  acid rain
- Examples:
1. Oil: petroleum
2. Natural Gas: made out of methane, cleaner than other fossil fuels
3. Coal: creates more than half of US’s electricity
Mechanical Energy
- Potential energy: stored energy, energy is NOT MOVING
o Gravitational PE: HEIGHT
 More height  greater PE
 Less height  less PE
-
Kinetic energy: energy of motion
o To increase KE: increase in velocity, larger mass
Conversions
o Roller coaster:
- Highest PE: at the top of hill
- Lowest PE: at bottom of hill
- Highest KE: at bottom of hill
- Lowest KE: at top of hill
- When rolling down the hill, PE converted into KE
- When car rolling up hill, KE converted to PE
o Pendulum
- Highest PE: at end of swings
- Lowest PE: at bottom of swing
- Highest KE: at bottom of swing
- Lowest KE: at end of swings
Waves
- Waves: REPEATING disturbance that carries energy from one place to another
o Cause: Vibrations
- Medium: matter waves pass through (Ex: air, water)
- Mechanical waves: require a medium (Ex: sound waves)
- Electromagnetic waves: DOES NOT require a medium (can travel through a vacuum)
- Transverse wave: particles of medium move up and down (perpendicular, at right
angles) to the direction of the wave
- Parts of a transverse wave:
-
o Wavelength: distance between 2 crests or 2 troughs
o Frequency: number of complete waves per unit time
- High Frequency = High energy
o
-
Longitudinal Wave: particles move PARALLEL (back and forth) to the direction of the
wave (Ex: sound waves)
o Parts of longitudinal wave:
 Rarefaction – particles are far apart
 Compression – particles are closer together
-
Electromagnetic spectrum: organized by frequency and wavelength
-
Radio waves: longest wavelength, lowest frequency and energy
o Radio, radar, TV, MRI’s
Microwaves: cell phones, satellite signals, microwave ovens
Infrared waves: felt as heat, used by remote controls and computers to read CD’s,
thermal imaging
Visible light: ROY G BIV
o Red: longest wavelength and largest frequency
o Violet: shortest wavelength and smallest frequency
Ultra-violet waves: needed by cells to produce vitamin D, too much  skin cancer
X-rays: images of internal organs, bones, teeth
Gamma rays: highest energy and frequency, shortest wavelength
o Result of nuclear reactions
-
Light
- Reflection: bouncing back of light
o Law of Reflection: angle of incidence = angle of reflection
-
Refraction: bending of light due to a change in
speed