Scientific Quantities and Units
Use scientific quantities with correct units: pair every measurement with its unit (metres, kilograms, seconds, newtons, joules), pick sensible prefixes like milli- and kilo-, convert between them, and call chemicals by their proper scientific names
What a learner can do afterwards
- Record measurements with the correct unit and symbol (e.g., 2.5 kg, 30 s, 1.2 m)
- Convert between prefixed units when comparing or calculating (e.g., 2500 mL = 2.5 L, 0.4 km = 400 m)
- Use proper chemical names for common substances in written work (e.g., sodium chloride rather than just 'salt')
1 · Read
When recording mass, length, time or force, write the number with its unit. A mass written as 12 alone could mean grams or kilograms. The unit identifies the scale of the measurement.
Length can be measured in metres, written m. Kilograms, written kg, measure mass. Seconds, written s, measure time. Choose a unit for the quantity you measured.
Mass and time are different quantities. A value in kg describes mass, while a value in s describes time. They cannot be converted into each other. Newtons, written N, measure force; joules, written J, measure energy.
Milli- means one thousandth of the named unit. There are 1000 millilitres in 1 litre. You may see ml or mL; both mean millilitres. To express a volume in L rather than mL, divide its numerical reading by 1000. For example, 1800 ÷ 1000 = 1.8, so 1800 mL = 1.8 L. The volume stays the same.
Kilo- means one thousand. There are 1000 metres in 1 kilometre. To express a length in m rather than km, multiply its numerical reading by 1000. For example, 0.6 × 1000 = 600, so 0.6 km = 600 m. The length stays the same.
Use an established chemical name when the substance's identity is known. Sodium chloride is the main compound in ordinary table salt. Salt also names a broader class of compounds, so the word alone does not identify sodium chloride. Baking soda is sodium bicarbonate.
Compare measurements after expressing them in the same unit. A millinewton, mN, is one thousandth of a newton. Divide the numerical reading in mN by 1000 to get the reading in N. For example, 500 ÷ 1000 = 0.500, so 500 mN = 0.500 N. This is the same force, not 500 N.
A kilogram contains 1000 grams. To express a mass in g rather than kg, multiply its numerical reading by 1000. For example, 1.25 × 1000 = 1250, so 1.25 kg = 1250 g. Defined conversions such as 1000 g = 1 kg do not change the physical mass.
Record the quantity and unit, convert before comparing, and use chemical names only when the substance's identity is known.
Rewritten readings were written for this dataset. Additional flashcards written for this dataset.
2 · Watch
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Where it sits
Where this leads
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.