chapter 2

foundations of physics

physical quantity + example

• a physical property,phenomenon, body / substance that can be quantified

• eg - voltage, height pressure

unit + example

• a definite magnitude of a physical quantity that is used as a standard measurement

• eg m, N, V

What are the base Units + symbols

• from SI(systeme internationale)

• Length - metre - m

• mass - kilogram - kg

• time - seconds - s

• electric current - Ampere(amps) - A

• temperature - Kelvin - K

• amount of substance - mole - mol

derived units vs base units

• base units - only the 6 units from SI

• common derived - using any units to break down another unit

power as common derived + base units

• power = watts

• watts = joules/second = Js^-1

• J = kgm²s^-2

• kgm²s^-2 * s^-1

• kgm²s^-3

How to add vectors

• tip to tail

• resultant force marked with double arrow

what forces can’t be resolved

• forces with only horizontal + vertical components

vector

• has magnitude + direction

scalar

• only has magnitude

prefixes + suffixes

Homogenity

• Use base units to check whether an equation representing physical quantities could be correct

• for an equation to be contact units must be the same type(homogenous)

estimation + orders of magnitude

• when estimating round estimate to the nearest power of 1-

• value should be accurate to the correct “order of magnitude” → within one power of 10 of the correct answer

Errors

• the difference between a computed value r a measured value and a true or theoretically accurate one

• random → unknown unpredictable changed during the experiment(give measurements above + below the true value)

• humans/one-off → error is caused by a simple mistake reading/recording a value

• Systematic errors → involve measuring instruments, something is wrong with the instruments/data handling instrument, instrument is wrongly used by conductor + present in all the readings taken and can be removed

• zero error - apparatus showing a non-zero value when should be registering exactly 0

Accuracy + precision

• accuracy → quantity being measured has a value that is very close to the commonly accepted/true value

• precision → related to how close together repeat values are( smaller spread + range)

Uncertainties

• absolute uncertainty - range/2 for repeats or smallest division on measuring instrument

• percentage uncertainty - absolute uncertainty/mean x 100

• when adding/subtracting readings (same units) add absolute unc

• when adding/subtracting readings(diff units) add % unc

• % unc in calcs - times by the power → eg x² - yx2 if y is %unc

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