1.4 SI Units, Measurement and Density

Notes

Scientists use SI units. Prefixes change the size of a unit by powers of 10.

• Base units: mass in kilograms (kg), length in meters (m), time in seconds (s), temperature in kelvins (K), amount in moles (mol).
• Prefixes: kilo (k) $= 10^3$, centi (c) $= 10^{-2}$, milli (m) $= 10^{-3}$, micro ($\mu$) $= 10^{-6}$, nano (n) $= 10^{-9}$.
• $1 \text{ mL} = 1 \text{ cm}^3$ and $K = °C + 273$.
• Accuracy is closeness to the true value; precision is closeness of repeated measurements to each other.
• Density: $\displaystyle D = \frac{m}{V}$. Example: a 54.0 g block with volume 20.0 $\text{cm}^3$ has $D = 2.70 \text{ g/cm}^3$.