Hooke’s law November 15, 2009

In mechanics, and physics, Hooke’s law of elasticity is an approximation that states that the extension of a spring is in direct proportion with the load added to it as long as this load does not exceed the elastic limit. Materials for which Hooke’s law is a useful approximation are known as linear-elastic or “Hookean” materials.

Mathematically, Hooke’s law states that

where

x is the displacement of the end of the spring from its equilibrium position;

F is the restoring force exerted by the material; and

k is the force constant (or spring constant).

Hooke’s law is named after the 17th century British physicist Robert Hooke. He first stated this law in 1676 as a Latin anagram,^[1] whose solution he published in 1678 as Ut tensio, sic vis, meaning, “As the extension, so the force”.When this holds, the behavior is said to be linear. If shown on a graph, the line should show a direct variation. There is a negative sign on the right hand side of the equation because the restoring force always acts in the opposite direction of the displacement (for example, when a spring is stretched to the left, it pulls back to the right).

Mach number November 4, 2009

Mach number (Ma or M) (generally pronounced /ˈmɑːk/, sometimes /ˈmɑːx/ or /ˈmæk/) is the speed of an object moving through air, or any fluid substance, divided by the speed of sound as it is in that substance. It is commonly used to represent an object’s (such as an aircraft or missile) speed, when it is travelling at (or at multiples of) the speed of sound.

An F/A-18 Hornet at transonic speed and displaying thePrandtl–Glauert singularity just before reaching the speed of sound

where

is the Mach number

is the speed of the source (the object relative to the medium) and

is the speed of sound in the medium

Units October 29, 2009

Source–http://www.essex1.com/people/speer/units.htmlMECHANICS

Parameter:	Metric Unit	British Units
time duration, delay	second * s	second, minute hour, day
frequency	hertz 1/s	cycle per second
length distance, displacement	meter 1/299 792 458 light sec m	inch, foot, yard rod, chain, furlong, mile
velocity, speed rate of change of position	meter per second m/s	foot per second mile per hour, knot
acceleration rate of change of velocity	meter per second squared m/s2	foot per second squared
mass quantity of material	kilogram * kg	ounce, pound, slug, ton
force push, pull, or weight	newton kg m/s2	pound-force
impulse force times time	newton second kg m/s	pound-force second
momentum mass times velocity	kilogram meter per second kg m/s	pound foot per second
work, energy force times distance	joule (pronounced “jewel”) = one newton meter kg m2/s2	foot pound-force
power rate of doing work	watt = one joule per second kg m2/s3	foot pound-force per second horsepower
area size of a surface	square meter m2	square foot, square yard acre, square mile
pressure force per unit area	pascal newton per square meter kg/m s2	pound-force per square inch
volume, capacity	cubic meter (stere) m3	pint, quart, gallon cubic foot, cubic yard
density, heaviness	grams per cubic centimeter g/cm3	pounds per cubic foot

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HEAT

Parameter:	Metric Heat Unit	British Heat Unit
heat energy	joule, j calorie, Calorie 1 cal = 4.186 joules 1 Cal = 4186 joules	British Thermal Unit, BTU
temperature change	kelvins, K *	Fahrenheit degree, Fº
temperature	kelvins, K	degrees Fahrenheit, ºF

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LIGHT

Parameter:	Metric Light Unit
luminous intensity	candle *
luminous flux	lumen one candle produces 4 pi lumens
illumination	lux lumen per square meter
focus	diopter reciprocal meters
astronomical distance	parsec

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ELECTRICITY & MAGNETISM (There are no British electrical units)

Parameter:	Metric Electrical Unit
electric charge	coulomb * 96,500 coul = 1 faraday faraday = 1 mole of electrons
electromotive force (EMF)	volt (joule per coulomb)
capacitance	farad (coulomb per volt)
electric current	ampere (coulomb per second)
electric energy	joule (watt second) (newton meter) KWH = 3,600,000 joules
electric power	watt (joule per second)
electrical resistance	ohm (volt per ampere)
electrical conductivity	siemens (coulomb per joule) (ampere per volt)
electrical field strength	volts per meter
electromagnetic inductance	henry (pl. henrys)
magnetic field intensity	oersted (formerly the gauss)
magnetic flux	weber (108 maxwells)
magnetic flux density	tesla weber per square meter
magnetomotive force	gilbert

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There’s more:

• Metric System
• Metric Areas and Volumes
• Metric Mass and Weight
• Metric Density and Specific Gravity
• Large and Small Numbers – Metric Prefixes
• Heat and Temperature
• Light and Optics
• Electricity and Magnetism
• Quarks and the Universe
• The Gordon Speer Home Page