This page lists physics misconceptions that frequently affect IGCSE students, organised by topic. For each misconception, we state the incorrect belief and the correct physics.
Topic 1: Motion, Forces and Energy
Misconception: “A force is needed to keep an object moving”
Correct physics: A force is needed to START an object moving or to CHANGE its motion. An object moving at constant velocity in a straight line has zero resultant force (Newton’s first law). In everyday life, we need to push things to keep them moving because friction is present, but the force we apply is balancing friction, not causing the motion.
Misconception: “Heavier objects fall faster”
Correct physics: In a vacuum, all objects fall with the same acceleration (g = 9.8 m/s^2) regardless of mass. In air, heavier objects MAY fall faster because they have a higher terminal velocity, but the acceleration due to gravity is the same.
Misconception: “If an object is not moving, no forces act on it”
Correct physics: A stationary object may have many forces acting on it. If it is stationary, those forces are balanced (the resultant force is zero). A book on a table has weight acting downward and a normal contact force acting upward.
Misconception: “Action and reaction forces cancel out”
Correct physics: Action and reaction forces (Newton’s third law) act on DIFFERENT objects, so they cannot cancel. Forces only cancel when they act on the SAME object in opposite directions.
Misconception: “Energy is used up”
Correct physics: Energy is never created or destroyed (conservation of energy). It is transferred from one store to another. When we say energy is “lost,” we mean it is dissipated to thermal energy in the surroundings, making it less useful.
Misconception: “Mass and weight are the same thing”
Correct physics: Mass is the amount of matter in an object (measured in kg). Weight is the gravitational force on an object (measured in N). Weight depends on the gravitational field strength: the same mass has different weights on Earth and on the Moon.
Topic 2: Thermal Physics
Misconception: “Heat and temperature are the same”
Correct physics: Temperature is a measure of the average kinetic energy of particles. Thermal energy (heat) is the total internal energy transferred. A bath of warm water has more thermal energy than a cup of boiling water, even though the cup is at a higher temperature.
Misconception: “Metal objects are naturally cold”
Correct physics: Metal objects feel cold because metal is a good thermal conductor. It conducts thermal energy away from your hand quickly. The metal is at room temperature, the same as a wooden object next to it, but the wood feels warmer because it conducts heat away from your hand more slowly.
Misconception: “Particles expand when heated”
Correct physics: Individual particles do not change size. When a substance is heated, the particles vibrate more and move further apart. The spaces between particles increase, causing the material to expand.
Topic 3: Waves
Misconception: “Waves carry matter from place to place”
Correct physics: Waves transfer energy, not matter. The particles of the medium oscillate about their rest positions but do not travel with the wave. A cork floating on water bobs up and down as a wave passes but stays in roughly the same place.
Misconception: “Sound can travel through a vacuum”
Correct physics: Sound is a mechanical wave that needs a medium (solid, liquid or gas) to travel through. It cannot travel through a vacuum. Light and other electromagnetic waves can travel through a vacuum.
Misconception: “Refraction changes the frequency of a wave”
Correct physics: When a wave crosses a boundary between two media, its speed and wavelength change, but its frequency stays the same.
Topic 4: Electricity and Magnetism
Misconception: “Current is used up as it goes around a circuit”
Correct physics: Current is the same at all points in a series circuit. Charge is not consumed; it flows continuously. What is transferred is energy: the charge gains energy at the battery and loses energy at the components.
Misconception: “Voltage flows through a wire”
Correct physics: Current flows through wires. Voltage (potential difference) exists ACROSS a component. It is the energy transferred per unit charge between two points.
Misconception: “A battery stores electricity”
Correct physics: A battery stores chemical energy. When connected in a circuit, chemical reactions produce a potential difference that drives a current.
Misconception: “Adding more resistors always increases total resistance”
Correct physics: Adding resistors in series increases total resistance. Adding resistors in parallel DECREASES total resistance (because the current has more paths to flow through).
Topic 5: Nuclear Physics
Misconception: “Radioactive materials glow green”
Correct physics: This is a fiction from films and television. Most radioactive materials look like ordinary materials. Radioactive decay is invisible to the naked eye and is detected with instruments like a Geiger-Muller tube.
Misconception: “Radioactive decay can be sped up or slowed down”
Correct physics: Radioactive decay is spontaneous and random. It is not affected by temperature, pressure, chemical reactions or any external conditions. The half-life is a fixed property of the isotope.
Misconception: “Radiation makes everything radioactive”
Correct physics: Being exposed to radiation does not normally make an object radioactive. An object becomes radioactive only if radioactive material is deposited on or inside it (contamination), not from being irradiated.
How to fix misconceptions
- Identify the misconception (use the list above as a checklist).
- Understand the correct physics (read the explanation, not just the statement).
- Practise exam questions that test the concept.
- Explain the correct physics to someone else (teaching is the strongest test of understanding).
Frequently Asked Questions
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Are these the same misconceptions every year?
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