# Physical Quantities and Units - Unit 1

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• Physical Quantities and Units - Unit 1
• Base Quantities
• independent quantities in terms of which other quantities can be defined
• Temperature, kelvin, K
• Time, seconds, s
• Mass, kilogram, k
• Length, metres, m
• Current, amperes, A
• Derived Quantities
• Quantities that are obtained by multiplying or dividing base quantities
• Velocity, v=s/t, ms^-1
• Energy (potential, e.g.), mgh, kgm^2s^-2
• Density, p=m/v, kgm^-3
• Volume, hxlxw, m^3
• Acceleration,a= (u-v)/t, ms^-2
• Frequency= 1/T, s^-1
• Prefixes
• Are used to form decimal multiples and submultiples of SI units
• kilo, k, x10^3
• Mega, M, x10^6
• Giga, G, x10^9
• Tera, T, x10^12
• deci, d, x10^-1
• centi, c, x10^-2
• mili, m, x10^-3
• micro, µ, x10^-6
• nano, n, x10^-9
• pico, p, x10^-12
• Estimations
• make reasonable estimates of physical quantities included within the syllabus
• Errors/Uncertainties
• Systematic errors are errors caused by the apparatus or the method used. It results in a complete shift of the results away from the true value
• To spot systematic errors, for a results graph where the gradient is constant, the y-intercept will not be 0. Can be corrected by correcting apparatus accordingly.
• Random errors are errors caused by the experimenter, causing a scatter of results around the true value.
• Can be corrected by taking many readings, discarding anomolies and taking an avg.
• The uncertainty of a scale is its smallest reading.
• Relative Error: Error/Actual Value
• Percentage error: Error/Actual Value) x100
• Addition/Subtraction -> Add up errors. Multiplication/Division -> Add up % errors.
• Precision/Accuracy
• Precision is how consistently a measurement is recorded.
• Precision refers to the degree of agreement of the results
• Precision refers to the degree of agreement of the results
• Accuracy is the degree of scatter about the true value
• Accuracy refers to how close the results are to the true value
• Accuracy is the degree of scatter about the true value