Units and Measurements

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A unit is a basic, arbitrarily chosen, internationally accepted reference standard used for comparison when measuring any physical quantity. We need units because: 1. To express the result of measurem

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**Fundamental Units:** - Units for base quantities that cannot be expressed in terms of other units - Examples: meter (m) for length, kilogram (kg) for mass, second (s) for time **Derived Units:** -

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The seven SI base units are: 1. **Length** - meter (m) 2. **Mass** - kilogram (kg) 3. **Time** - second (s) 4. **Electric Current** - ampere (A) 5. **Thermodynamic Temperature** - kelvin (K) 6. **Amo

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**Plane Angle:** radian (rad) - Defined as ratio of arc length to radius: θ = s/r **Solid Angle:** steradian (sr) - Defined as ratio of area on sphere to square of radius: Ω = A/r² **Not base units

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**SI System Advantages:** 1. **Universal acceptance** - Used internationally in science, technology, and commerce 2. **Decimal system** - Easy conversions using powers of 10 3. **Coherent system** - D

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**Significant Figures:** All digits in a measured value that are known reliably plus the first uncertain digit. **For 0.00308:** Number of significant figures = **3** **Analysis:** - Leading zeros (

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**1200:** 2 significant figures - Trailing zeros without decimal are NOT significant - Only 1 and 2 are significant **1200.:** 4 significant figures - Decimal point makes trailing zeros significant

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**Given:** - Mass = 4.237 g (4 significant figures) - Volume = 2.51 cm³ (3 significant figures) **Calculation:** Density = 4.237 ÷ 2.51 = 1.68804... g/cm³ **Rule for multiplication/division:** Resul