Foundations of Scientific Inquiry and Measurement · 3 min read
Laboratory Safety · Measurement and Units · Significant Figures and Uncertainty
Laboratory safety is essential for physics instruction. Teachers must model and enforce safety protocols.
Personal protective equipment requirements depend on the activity. Safety goggles protect eyes during any activity involving projectiles, chemicals, or breakable materials. Heat-resistant gloves are necessary when handling hot objects. Closed-toe shoes protect feet from falling objects.
Electrical safety requires inspecting equipment for frayed wires or damaged insulation, keeping water away from electrical sources, using appropriate fuses and circuit breakers, never exceeding rated voltages or currents, and disconnecting power before modifying circuits.
Radiation safety applies to activities involving radioactive sources, lasers, or UV light. Radioactive sources must be handled with tongs, never pointed at people, and stored in shielded containers. Lasers require appropriate wavelength-specific eyewear and should never be directed at eyes or reflective surfaces.
Mechanical safety involves securing heavy equipment, using appropriate clamps and supports, keeping work areas clear, and ensuring proper ventilation for activities generating dust or fumes.
Chemical safety in physics labs typically involves batteries (acid exposure), liquid nitrogen (cryogenic burns), and mercury thermometers (toxic exposure). Material Safety Data Sheets (MSDS) provide specific handling requirements.
The International System of Units (SI) provides standardized measurement units for scientific communication. Seven base units define all other units:
| Quantity | Unit | Symbol |
|---|---|---|
| Length | meter | m |
| Mass | kilogram | kg |
| Time | second | s |
| Electric current | ampere | A |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Luminous intensity | candela | cd |
Derived units combine base units. Examples include:
- Velocity: m/s
- Acceleration: m/s²
Metric prefixes scale units by powers of ten:
| Prefix | Symbol | Factor |
|---|---|---|
| tera | T | 10¹² |
| giga | G | 10⁹ |
| mega | M | 10⁶ |
| kilo | k | 10³ |
| centi | c | 10⁻² |
| milli | m | 10⁻³ |
| micro | μ | 10⁻⁶ |
| nano | n | 10⁻⁹ |
| pico | p | 10⁻¹² |
Unit conversion requires multiplying by conversion factors equal to one. To convert 5.0 km to meters: 5.0 km × (1000 m / 1 km) = 5000 m. Dimensional analysis verifies that units cancel appropriately.
Significant figures indicate measurement precision. Rules for identifying significant figures:
Trailing zeros in whole numbers are ambiguous without decimal points or scientific notation: 300 may have one, two, or three significant figures
Scientific notation eliminates ambiguity. Writing 3.00 × 10² clearly indicates three significant figures.
Calculation rules:
Measurement uncertainty quantifies the range within which the true value likely falls. For a measurement of 25.3 ± 0.1 cm, the true value is expected between 25.2 cm and 25.4 cm.
Percent error compares measured values to accepted values: Percent error = |measured – accepted| / accepted × 100%
Percent difference compares two measured values: Percent difference = |value₁ – value₂| / average × 100%
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