Measurement & Vectors – Key Vocabulary

Vocabulary flashcards covering SI base concepts, prefixes, error types, uncertainty, accuracy vs precision, vector–scalar ideas, and calculation rules from the measurement lecture.

Prefix

A symbol placed before an SI unit to represent a power of ten, allowing expression of very large or small values.

Accuracy

How close a measured value is to the true or accepted value; limited mainly by systematic errors.

Absolute Uncertainty

The numerical value of the uncertainty expressed in the same units as the measurement (e.g., 2.35
\pm
0.02 m).

Uncertainty (
\Delta
)

The estimated range within which the true value of a measurement lies, expressed as a
\pm
value.

Base Quantity

A fundamental physical quantity that can be accurately reproduced and is invariant with time; seven are chosen for the SI system.

Giga (G)

SI prefix meaning 10
\text{\textasciicircum}9
.

Apparent shift in a reading due to the observer

’s eye not being perpendicular to the scale, a source of random error.

Parallax Error

deci (d)

SI prefix meaning 10
\text{\textasciicircum}-1
.

Least Significant-Figure Rule

For multiplication or division, the result should match the least number of significant figures among the inputs.

Fractional/Percentage Uncertainty for Products/Quotients

If
R = XY
or
R = X/Y
, then the percentage/fractional uncertainty is
\frac{\Delta R}{R} = \frac{\Delta X}{X} + \frac{\Delta Y}{Y}..

Zero Error

A systematic error where a measuring instrument does not read zero when the quantity measured is zero.

Precision

How closely repeated measurements agree with each other; improved by reducing random errors.

Tera (T)

SI prefix meaning 10
\text{\textasciicircum}12
.

kilo (k)

SI prefix meaning 10
\text{\textasciicircum}3
.

pico (p)

SI prefix meaning 10
\text{\textasciicircum}-12
.

milli (m)

SI prefix meaning 10
\text{\textasciicircum}-3
.

Base Unit

The SI unit assigned to a base quantity (e.g., kilogram for mass, metre for length).

Physical quantity described by both magnitude and direction (e.g., displacement, force).

Vector Quantity

Relative Velocity (
\vec{v}\_AB)

The velocity of object A as observed from object B, given by
\vec{v}*A – \vec{v}*B
.

Absolute Uncertainty for Sums/Differences

If
R = X
\pm
Y
, then the absolute uncertainty is
\Delta R = \Delta X + \Delta Y
.

centi (c)

SI prefix meaning 10
\text{\textasciicircum}-2
.

Derived Quantity

Any physical quantity defined in terms of the seven base quantities (e.g., velocity, force).

Systematic Error

Consistent deviation of readings in the same direction due to equipment or procedural fault; affects accuracy.

Best-Fit Line

A line drawn through plotted data points that balances points above and below it, reducing the influence of random errors.

femto (f)

SI prefix meaning 10
\text{\textasciicircum}-15
.

micro (µ)

SI prefix meaning 10
\text{\textasciicircum}-6
.

Homogeneity of an Equation

Condition in which every term in a physical equation has identical base units; required for correctness but not a guarantee of validity.

nano (n)

SI prefix meaning 10
\text{\textasciicircum}-9
.

Vector Triangle (Equilibrium)

A closed triangle formed by vectors indicating zero resultant; if open, a resultant vector exists.

Least Decimal-Place Rule

For addition or subtraction, the result should match the least number of decimal places among the inputs.

Percentage (Fractional) Uncertainty

The ratio of absolute uncertainty to the measured value, expressed as a percent or fraction.

Fractional/Percentage Uncertainty for Powers

If
R = X
\text{\textasciicircum}n
, then the percentage/fractional uncertainty is
\frac{\Delta R}{R} = n \frac{\Delta X}{X}.