Glossary

1.1 What is Biomechanics

biomechanics
the application of principles of mechanics to the study of living systems

mechanics
the branch of science concerned with the interaction between forces and objects

1.2 Physical Quantities and Units

physical quantity

characteristic or property of an object that can be measured or calculated from other measurements

SI units

the international system of units that scientists in most countries have agreed to use; includes units such as meters, liters, and grams

base quantity

physical quantity chosen by convention and practical considerations such that all other physical quantities can be expressed as algebraic combinations of them

base unit

standard for expressing the measurement of a base quantity within a particular system of units; defined by a particular procedure used to measure the corresponding base quantity

derived quantity

physical quantity defined using algebraic combinations of base quantities

derived units

units that can be calculated using algebraic combinations of the fundamental units

English units

system of measurement used in the United States; includes units of measure such as feet, gallons, and pounds

kilogram

SI unit for mass, abbreviated kg

meter

SI unit for length, abbreviated m

metric system

system in which values can be calculated in factors of 10

second

the SI unit for time, abbreviated s

units

standards used for expressing and comparing measurements

1.3 Accuracy and Precision

accuracy

the degree to which a measured value agrees with an accepted reference value for that measurement

range
the difference between the lowest and the highest measured values

discrepancy

the difference between the measured value and a given standard or expected value

method of adding percents

the percent uncertainty in a quantity calculated by multiplication or division is the sum of the percent uncertainties in the items used to make the calculation.

percent uncertainty

the ratio of the uncertainty of a measurement to the measured value, expressed as a percentage

precision

the degree to which repeated measurements agree with each other

significant figures

used to express the precision of a measuring tool used to measure a value

uncertainty

a quantitative measure of how much measured values deviate from one another

average (arithmetic mean) 
The sum of all the measures divided by the number of measurements

mean absolute difference
The absolute value of the uncertainties for each measure, and then reporting the average of those

variance
The average of the squares of the difference from the mean.

standard deviation 
The square root of the variance

1.4 Conversions

conversion factor

a ratio that expresses how many of one unit are equal to another unit