formulas and units Flashcards by rafaela thomas

state hookes law

force= constant * extension
F=Kx

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formula for moment

force * distance from pivot (at 90degrees)
F1d1 = F2d2
F1d1 + F2d2 = F3d3

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pythagoras

aˆ2 = bˆ2+ cˆ2

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force

mass x acceleration
mass=kg, a =m/s2

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weight

mass * gravity
gravity= 9.8m/sˆ2

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momentum

mass x velocity

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impulse

= Force x contact time = change in momentum

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velocity/speed

distance/time

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acceleration

change in velocity / change in time

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density

mass/volume

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pressure laws in gas

1/volume
p1v1=p2v2

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work

Force x distance (parallel to Force)

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potential energy

mass x gravity x height

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kinetic energy

= ½ x mass x (velocity)2

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power. 4

work done/time taken
current * voltage
current ˆ2 * resistence
voltage ^2/ resistence

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pressure

force/ area

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pressure in liquids

= density x gravity x depth

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current

charge/ time

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potential difference (voltage)

work done/ charge

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e.m.f

work done/ charge

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ohms law

voltage= current * resistence

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resistance

voltage/current

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energy

voltage * current * time

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resistence laws

bigger the length of wire, bigger the resistence
bigger the diameter of wire smaller the resistence

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resistence in series

r= r1 +r2

resistence in parallel

r= r1 *r2/ r1+r2

potential divider

v out= (r1/ r1 + r2) * v in r1/r2= v1/v2

heat energy

mass x specific heat capacity x temperature change

efficiency

(useful Energy (or power) output/ Energy (or power) input) * 100%

wave speed

frequency x wavelength

frequency

number of oscillations/ time taken 1/T

refractive index

sin 1/ sin r v1/v2 1/sin c

speed of light in a vacum

3 * 10ˆ8 m/s

speed of sound in air

330 to 350 m/s

human audible range

20-20000 hz

transformers

number of turns in primary coil/ number of turns in secondary coil = voltage in primary coil/ voltage in secondary coil voltage1 * current 1= voltage 2 * current2

orbital speed

2 π r/ period time

hubbles constant

speed/ distance

age of universe

distance/ speed 1/hubbles constant

hubbles constant number

2.2 x 10ˆ-18 per second

one light year is...

9.5 x 1015 m

milky way galaxy diameter

100 000 light years

mega

* 1000 000

kilo

* 1000

mili

/1000

unit for force and weight

newtons (N)

mass unit

g or kg

temperature unit

degrees or kelvin (k)

frequency unit

hertz (hz)

velocity speed unit

m/s or km/h

acceleration unit

m/s ˆ2

current

amps (A)

p.d votlage unit

volts (V)

charge unit

columbs (c)

resistence unit

ohms (Ω)

moments unit

momentum unit

kg m/s

power unit

watts (w)

density unit

g/cm3 , kg/m3

pressure units

Pascals (Pa), N/cm2

work and energy unit

joules (J)

electrical energy unit

kWh

specific heat capacity

J/kg0C, J/g0C