General Science • Topic 1 of 4

Physics Basics

Know the SI units and basic laws: force is measured in newtons (N), energy in joules (J), power in watts (W). Newton's second law gives Force = mass × acceleration (F = ma). The speed of light is about 3 × 10⁸ m/s; sound is far slower (~343 m/s in air).

SI units you must know cold

QuantitySI unitMeasured by
Forcenewton (N)—
Energy / Workjoule (J)—
Powerwatt (W)—
Temperaturekelvin (K)thermometer
Electric currentampere (A)ammeter
Atmospheric pressurepascal (Pa)barometer

Newton's three laws in one line each

  • First law (inertia): a body stays at rest or in uniform motion unless a force acts.
  • Second law: Force = mass × acceleration (F = ma).
  • Third law: every action has an equal and opposite reaction.
Light vs sound. Light ≈ 3 × 10⁸ m/s; sound ≈ 343 m/s in air. That gap is why you see lightning before you hear thunder. Sound travels fastest in solids, slowest in gases, and not at all in a vacuum.

✅ Solved examples

1. What is the SI unit of force?
The newton (N).
2. State Newton's second law as a formula.
Force = mass × acceleration (F = ma).
3. Which instrument measures atmospheric pressure?
The barometer.
4. What is the approximate speed of light?
About 3 × 10⁸ metres per second.

✏️ Practice — try these, take hints as needed

1. The SI unit of energy is the?
Named after Joule.
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—
Joule (J)
2. Newton's first law is the law of?
Resistance to change.
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Inertia
3. An ammeter measures?
Flow of charge.
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Electric current
4. The SI unit of power is the?
Watt.
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Watt (W)
5. Sound travels fastest in which medium?
Solid/liquid/gas.
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Solids

📝 Topic test — 8 questions

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