3.2 
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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
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1 - Science of Physics
2 - Forces and Motion3 - 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
Friction and losses
Examples of friction Examples of friction: rock climbing (static friction); baseball player sliding (sliding friction); sky diving (air friction); swimming (viscous friction); and car tire (rolling friction). Friction is all around us in many different forms. A sky diver's fall is slowed down by air resistance when he descends stomach-first. The brake pads on a car slow down the car by rubbing against the rotors in the wheel. A swimmer or a submarine are slowed down in water by fluid friction called viscosity. When you walk, the friction between the sole of your shoe and the ground stops you from sliding—unless you step on a patch of ice! Show Friction and drag
Meaning of friction Microscopic view of friction Friction is a “catch-all” term we use to describe forces that are created by motion and that act to resist motion. Since work and energy are closely related, frictional forces represent work done by a moving object on the surroundings. As a result, some energy in the moving object is transformed to other forms of energy in order to overcome friction. A car slows down when the bakes are applied, which is equivalent to saying that the car does work to overcome friction, thereby losing some of its kinetic energy. Show Microscopic view of friction
What happens to energy used to overcome friction? Work done against friction usually converts kinetic energy into thermal energy (heat). When you rub your two hands together, the friction between them causes them to warm up. The energy used to overcome friction is sometimes called “energy losses”; strictly speaking, however, energy is still conserved. The work done by frictional forces on the surroundings exactly matched the energy gained by the surroundings. The thermal energy gained by the surroundings, however, usually flows out of the system and is “lost” in terms of being available to do other work. Show Brake fade and glazing
Test your knowledge Katie pushes on a 10 kg box with 60 N of force, but the box only accelerates by 3 m/s2. How much friction is there?
  1. 2 N
  2. 6 N
  3. 20 N
  4. 30 N
Show
Solved Problem 3.4: Energy losses due to viscous friction
A swimmer applies 100 N of force to swim 25 m across the pool, but the water's viscous friction drags against him with a force of 40 N. (a) How much total work did the swimmer do in crossing the pool? (b) How much work did the swimmer waste in overcoming viscous friction?

Asked: (a) Total work done by the swimmer (b) Work done overcoming viscous friction Force diagram for swimmer solved problem
Given: Force applied by swimmer: Fs=100 N. Resistive force due to viscous friction from water: Ff=40 N.
Relationships: Work: W=Fd
Solution: (a) The total work done by the swimmer is calculated using the total force Fs
exerted by the swimmer :
W tot = F s d=(100 N)(25 m)=2,500 J

(b) The work done by the swimmer to overcome viscous friction, Ff, is
calculated using the resistive force due to the water:
W f = F f d=(40 N)(25 m)=1,000 J
Answer: (a) 2,500 J. (b) 1,000 J.

Discussion. The swimmer spent 2,500 J - 1,000 J = 1,500 J of output work in actually moving his body across the pool, which corresponds to a fraction of his input work of 1,500 J/2,500 J = 0.6. We say that his swimming was 60% efficient in converting input work to output work.

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