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

3.3 - The flow of energy

Scientists learn a great deal by following the flow and transformation of energy. All processes in both nature and technology operate through a continuous flow of energy. A system can transform its available energy into speed, height, heat, or even mass. The system must have energy to begin with, and any energy transformed into one form must deplete other forms by the same amount. This section examines how electrical, thermal, and light energy are transformed through technologies such as the photovoltaic cell, which converts radiant energy into electrical energy.
Energy flow diagrams
Mechanical energy	Consider the sewing machine, one of the most revolutionary devices ever invented. Clothing is a basic human need and prior to the sewing machine all clothes were stitched together by hand. Hand sewing requires considerable skill and takes a long time. A single shirt might take several hours to sew by hand. The same shirt can be sewn on a machine in six minutes with perfect, uniform stitches.
Energy flow in muscle work	Sewing requires mechanical work—forcing a needle through cloth. To estimate the energy involved, assume a weight of 30 N for your forearm and hand. Your hand moves about 40 cm to make a stitch so each stitch represents about 12 J of muscle work. If you average a stitch every 2 seconds that is an energy flow of 6 joules per second.
	That muscular energy comes from food which derives ultimately from sunlight so the flow of energy through your muscles traces its way back to nuclear energy in the sun.
Energy flow in technology	Transforming energy from one form to another is depicted in an energy flow diagram or described as an energy chain. The energy used by the sewing machine comes from an electric motor that converts electrical energy to mechanical energy. Two-thirds of US electricity is generated from burning coal or natural gas. The fossil fuel itself came from decaying plants. Burning fuel transforms chemical energy into thermal energy, and the heat produced boils water into steam. The steam turns a turbine that converts pressure energy into mechanical energy; the turbine drives a generator to produce electrical energy. The electrical energy we use is ultimately derived from nuclear energy in the Sun, transported to the Earth as radiant energy, accumulated by plants over millions of years, then stored in fossil fuels.
Energy content of goods	How much total energy has been used up to the point of actually sewing together a shirt? This is not an idle question. Buying a shirt is using energy because it takes energy to farm the cotton, weave it into cloth, ship the cloth to a factory, produce the shirt, and then ship it to the store. We humans are learning that the energy content in what we buy must ultimately come from some source, often fossil fuels. One of the major goals of engineering and technology today is to apply science to reduce the energy content of goods we produce and use.
Test your knowledge	Where does the vast majority of Earth's energy originate? The Moon The Earth's core The atmosphere The Sun
	The correct answer is d, the Sun. Most of Earth's energy originates in the nuclear fusion inside the Sun. That energy then gets transported across space via electromagnetic waves and changed into all the different types we use everyday.