Wednesday, August 8, 2012


One of the most important intuitions to build through studying physics are approximations of what things are. Its important to know how big or small something roughly is or how fast or slow it is moving. This allows us to better perform "back of the envelope" calculations; popularized by Enrico Fermi, these calculations are useful in determining the behaviors of a system. Its not necessary to memorize all of these, but it helps to get a scale of the world.

10-10 meters - Angstrom, roughly the size of an atom
10-9 meters - Nanometer, few times larger than the largest atoms
10-8 meters - Size of some transistors in computer chips
10-6 meters - Micrometer, Micron, size of bacterias/cells
10-3 meters - Millimeter, size of the point pen/edge of penny
10-2 meters - size of a finger
100 meters - meter, size of people
103 meters - kilometer, length of a 10 minute walk
107 meters - Diameter of Earth
1011 meters - Distance to sun

10-24 kilogram - weight of buckyball
10-9 kilogram - weight of grain of dust
10-6 kilogram - weight of grain of salt
10-3 kilogram - weight of grain of dust
100 kilogram - weight of chihuahua
103 kilogram - weight of car
106 kilogram - weight of space shuttle
1024 kilogram - weight of Earth

10-3 m/s - speed of snail
100 m/s - speed of human walking
101 m/s - speed of cheetah
102 m/s - speed of car
103 m/s - speed of airplane
106 m/s - speed of electron
3*108 m/s - speed of light

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