Physics

• Speed = distance ÷ time. Rearranged: distance = speed × time.
• First law — a body stays at rest or in uniform motion unless a force acts. Also called the law of inertia.
• Second law — force produces acceleration; F = ma.
• Third law — every action has an equal and opposite reaction.
• Mass is the amount of matter and never changes. Weight is the pull of gravity and does. On the Moon your weight is about a sixth of Earth's; your mass is identical.
• Density = mass ÷ volume.

• Kinetic energy — energy of motion. Potential energy — energy of position or shape.
• A stretched rubber band or a compressed spring holds elastic potential energy.
• Energy is neither created nor destroyed, only converted.
• Power is the rate of doing work — joules per second. A higher wattage means energy used faster, not more energy in total.

• Plane mirror — image the same size, upright, laterally inverted, and as far behind as the object is in front.
• Convex mirror — always upright and smaller, wider field of view. Used as a vehicle rear-view mirror.
• Concave mirror — can magnify; used in torches and shaving mirrors.
• Convex lens converges light; concave lens diverges it.

• Conduction needs contact; convection needs a moving fluid; radiation needs nothing — which is how the Sun's heat crosses empty space.
• Sea and land breezes are convection.
• A clinical thermometer reads 35 °C to 42 °C; a laboratory one covers a much wider range less precisely.
• A fuse is made of low-melting-point wire so it melts and breaks the circuit under too much current.
• Series — one path, so one failed bulb stops everything. Parallel — separate paths, so the others stay lit.
• Like magnetic poles repel, unlike attract. A suspended magnet settles north–south.

These are the mistakes, not the rules — each one is something a student who knows the topic still does under time pressure.

1. Saying mass is less on the Moon. Weight changes; mass does not.
2. Mixing up the units: the joule is energy and the watt is power.
3. Thinking sound travels through a vacuum. It needs particles; light does not.
4. Choosing a concave mirror for a vehicle. A convex one gives the wide, upright view.
5. Saying the Sun's heat reaches us by convection. Space is empty — it must be radiation.