3.1

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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

Work

Work and energy

How does energy move and create change? The answer starts with the physical idea of work. In physics, work is done by forces that cause objects to move. As shown in equation (3.1), the amount of work done on an object is the force multiplied by the distance the object moves in the direction of the force. If you use a force of one newton to lift a cup up distance of one meter, you do one newton-meter (N·m) of work on the cup. Read the text aloud

Read the text aloud

Show Can a force do no work?

W = F d

W	=	work (J)
F	=	force (N)
d	=	distance (m)

The meaning of the word “work” is different in physics than in everyday life. You might complain that you work too hard on your homework, or that you have to go to work early in the morning. In physics, work is the product of force exerted and distance moved, and it can have a precise value such as 10 newton-meters (N·m). Work is done whenever energy is transferred from one object to another. Read the text aloud

Read the text aloud

Force, work, and energy

In the SI system, one joule (J) is defined as one newton-meter (N·m). The unit of work—the joule—is also the basic unit of energy. Throughout physics and throughout all of science—including chemistry, biology, and earth sciences—you will find the joule as a standard unit of energy. It is not, however, the only unit of energy. Calories (food), British thermal units (heat), and kilowatt-hours (electricity) are other units of energy that are commonly used. Read the text aloud

Read the text aloud

Work is force times distance moved

Work provides an operational definition for energy: energy is the stored ability to do work. If you have 10 joules of energy, you have the ability to produce a force of 10 newtons for a distance of 1 meter, or 1 newton for 10 meters. A system that has 1 joule of energy can exert any combination of forces and distances whose product is equal to or less than 1 newton-meter. We say “less” because the amount of energy available limits the amount of work that can be done. No system can produce any work that exceeds its available energy. Read the text aloud

Read the text aloud

Show Other ways to define energy

Tim pulls his little sister in a wagon with a constant force of 50 N over a distance of 100 meters. How much work does Tim do?

5,000 J
2,500 J
150 J
50 J

Show

Asked: Work W done on cart
Given: Tim exerts force F = 50 N, force exerted over distance d = 100 m
Relationships: W = Fd
Solve:

\begin{array}{l} W & = & F d \\ = & (50 N) \times (100 m) \\ = & 5, 000 J \end{array}