Flashcards · 7357 · Topic 17

P: Quantities and units in mechanics flashcards

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The fundamental quantities and their SI units: Mass: kilogram (kg). Length: metre (m). Time: second (s).
Derived SI units of velocity, acceleration and force: Velocity: m s⁻¹. Acceleration: m s⁻². Force: newton, 1 N = 1 kg m s⁻².
Weight: W = mg, a force measured in newtons, acting vertically downwards. With g = 9.8 m s⁻², a 5 kg mass has weight 49 N.
Convert 54 km h⁻¹ to m s⁻¹.: Divide by 3.6: 54 ÷ 3.6 = 15 m s⁻¹.
How can units check a formula?: Every term must have the same units. In v² = u² + 2as each term is in m² s⁻², so the formula is consistent.
Mass vs weight: Mass is the amount of matter, in kg, and does not change. Weight is the gravitational force mg, in N.