3.3

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Videos: Conservation of energy Elastic potential energy Elastic potential energy in your bicep and tricep muscles Energy and work Gravitational potential energy Kinetic energy Physics of wind power Solar flare is a plasma in motion Steam rising out of cooling tower at a nuclear power plant

Investigations: 3A: Work and the force vs. distance graph (p. 113) 3B: Inclined plane and the conservation of energy (p. 118) 3C: Work and energy for launching a paper airplane (p. 122) 3D: Springs and the conservation of energy (p. 124) 3E: Conservation of momentum (p. 128) 3F: Collisions (p. 132) 3G: Shock absorbers and dampers (p. 139) 3H: Specific heat of water and steel (p. 144)

Science: Algebra derivation using the conservation of energy Brownian motion Choosing origin for potential energy reference frame Difference between heat and temperature Einstein's theory of relativity Elastic potential energy Elastic potential energy in your muscles Elastic potential energy in your muscles Energy and power for light bulb Energy and work Energy content of phases of matter Energy flow in open and closed systems Faster than light travel? Forms of energy Friction Galileo and the Leaning Tower of Pisa Gravitational potential energy Hooke's Law for springs Intensity of sunlight at Earth's surface Kelvin temperature scale and absolute zero Kinetic energy Law of conservation of energy Loose springs and stiff springs (BLM) Ordered and random kinetic energy Other conservation laws in physics Plasma in motion during a solar flare Plasma is a phase of matter Potential energy Power and radiant energy Power is the rate of doing work Radiant energy Relationship between momentum conservation and Newton's third law Symmetry in the physics of collisions Units of work and energy van der Waals forces

Technology: Batteries and electrical power Calories on food labels Conserving energy in everyday life Converting units and understanding energy content from food Efficiency in technology Energy content of everyday goods Energy flow in clothing manufacture Energy transformations in an internal combustion (piston) engine Energy transformations in technology usually produce heat Everyday objects that store energy Everyday technology in our age of energy Friction from brake pads in a car's wheel Hydroelectric dam Objects with elastic potential energy Power in everyday technology Power, wattage, and the light bulb Radiant power and the light bulb Technology and agriculture over the last century

Engineering: Calculating energy production for the Hoover Dam Design a wind turbine power plant Efficiency Electric current Electromagnetic spectrum Open and closed systems Siting constraint for power plants Specific heat Springs Volts, amps, and power

Mathematics: Algebra derivation using the conservation of energy Calculating energy production for the Hoover Dam Changes in a quantity represented by Greek symbol Δ Choosing origin for potential energy reference frame Converting units and understanding energy content from food Deducing a physical equation Different rates of change Hooke's Law for springs Non-linear relationships Proportional relationships Using algebra to derive temperature conversion formula Using algebra to solve for a variable

Interactive Simulations Interactive simulation of motion down an inclined plane Motion down an inclined plane Interactive simulation of an oscillating spring Spring-loaded carts simulation Elastic collisions between two balls Inelastic collisions between two balls Interactive simulation of an oscillating spring Interactive simulation of an oscillating spring Wind power design simulation Interactive Calculators Work equation calculator Kinetic energy equation Potential energy equation Elastic potential energy equation Efficiency equation Conservation of momentum in collisions equation Power equation calculator
Electric power equation Temperature conversion equation Specific heat equation

1 - Science of Physics
2 - Forces and Motion 3 - Energy Transformations Chapter 3 at a glance 3.1 - Energy 3.2 - Conservation of energy 3.3 - Flow of energy 3.4 - Temperature and the kinetic theory of matter 3.5 - Chapter review4 - Waves and Sound
5 - Electricity and Magnetism
6 - Light and Optics
7 - The Atom
8 - Linear Motion
9 - Vectors and Forces
10 - Forces
11 - Newton's Laws and Gravitation
12 - Circular Motion and Gravitation
13 - Torque and Static Equilibrium
14 - Momentum and Collisions
15 - Angular momentum
16 - Power and Machines
17 - Harmonic Motion
18 - Waves
19 - Sound
20 - Electricity
21 - Electric and Magnetic Fields
22 - Electromagnetism and Induction
23 - Light and Color
24 - Geometrical Optics
25 - Electromagnetic Radiation
26 - The Properties of Matter
27 - Thermodynamics and Heat Transfer
28 - The Atom
29 - The Quantum Theory
30 - TBD
31 - TBD
32 - TBD
33 - TBD
34 - TBD
35 - TBD
36 - TBD
37 - The atomic nucleus and radioactivity
38 - Nuclear reactions
39 - Relativity
40 - Particle physics and the standard model
41 - Electronics (semiconductors)
42 - Nuclear technology
43 - Lasers and photonics
44 - Metals, alloys and materials science
45 - Communications technology
46 - Buildings and structures
47 - Energy technology
48 - Biophysics
49 - Matter and Energy, Space and Time
50 - Energy Transformations
51 - Nanotechnology
52 - Website Videos
53 - ExtraStuff
55 - Modeling Motion, Friction, and Center of Mass
56 - Work and the Conservation of Energy

Light energy and power

Radiant energy	Light is a form of radiant energy that is all around us almost all the time. Radiant energy has no mass and can travel unimpeded through the vacuum of space. Visible light is a small part of the whole spectrum of radiant energy that includes microwaves, infrared radiation, and ultraviolet light—as well as more exotic forms such as x-rays and gamma rays. The human eye responds to a narrow band of energy that starts in the dull red, then proceeds through orange, yellow, green, blue, and violet. Blue-violet is the most energetic light you can see. Light of higher energy falls into the ultraviolet (UV) range and it can give you a sunburn, but you cannot see it with your eyes.

Power and radiant energy	Radiant energy always travels at the speed of light, which is 300,000,000 m/s or 3×10⁸ m/s. Nothing in the known universe can travel faster than light. Since light is energy that is always moving, it is best described in terms of its power. An old-fashioned, incandescent 100 watt light bulb produces a power output of about 2 or 3 watts of visible light; the remaining input power is transformed into thermal energy. The Sun produces an incredible amount of power—about 3.8×10²⁸ watts.
Faster than light travel?	Fans of science fiction books and movies know that many stories include a technology—such as a warp drive!—by which the characters can travel across the Galaxy faster than the speed of light. In the real world, can anything actually travel faster than light? No! Light is massless, and only things that are massless can travel at the speed of light; everything else has mass and must travel slower. This is a basic postulate of Albert Einstein's theory of special relativity. That said, a group of physicists recently announced a preliminary result on the speed of a particular kind of elementary particle, called the neutrino. The researchers believe they have measured some neutrinos traveling faster than the speed of light between the CERN particle collider in Switzerland and their detectors in Italy. Many physicists are skeptical about these initial results, because they are contradicted by a previous result: the speed of neutrinos emitted by a supernova (an exploding star) in 1987 were shown not to travel faster than light. The previous results had been much more precise, due to the long travel time of those neutrinos across the Galaxy. Which result is right? Can neutrinos travel faster than light or not? Stay tuned!
Intensity	Intensity is power per unit area. An intensity of 1 watt per square meter (1 W/m²) means 1 watt of light power crosses or lands on each square meter of surface. When we say a light is bright or dim, what we really mean is that the intensity of the light is either low (dim) or high (bright). The intensity of bright sunlight can be as high as 600 W/m². Imagine that: sunlight delivers the energy of six light bulbs onto every square meter of the Earth. This is the reason that solar energy has great potential as a renewable energy source.
Intensity and the human eye	Your eye is an incredibly sensitive detector of light energy. The light receptor cells in the back of your retina can detect an intensity of 10⁻⁹ W/m², one billionth of a watt per square meter. Since the area of the retina is very small, this corresponds to a power of less than a trillionth of a watt!
Color and energy	Apart from whether the light is bright or dim, light has an intrinsic energy that produces the perception of color in your eye. The sensation of color is created by the brain in response to the differing energy content in the light. The lowest energy light humans can see is dull red. The highest energy light you can see is violet. A human eye is most sensitive to green light, which is is in the middle of the visible energy spectrum. What we perceive as white light is actually an even mixture of light of different energies.
Test your knowledge	Which color light has more intrinsic energy, red or blue?
	Blue light has more intrinsic energy than red light because it has a higher frequency.