Physical Sciences
Physical Sciences
This domain tests how matter behaves, how forces change motion, and how energy is transferred in light, sound, heat, electricity and magnetism. Items usually set the idea in an everyday context - a melting ice cube, a lamp in a circuit, a magnet near a nail - and ask you to explain the process rather than just name it.
Matter and changes
- All matter is made of particles too small to see. In solids the particles are packed and vibrate; in liquids they slide past one another; in gases they move quickly and fill the container. Gases have mass.
- A physical change alters size, shape or state but not the substance (ice melting, sugar dissolving). A chemical change forms a new substance and often shows burning, rusting, bubbling, a new colour or a temperature change.
- Mixtures keep their parts and can be separated by hand, sieving, filtration, magnetism or evaporation. In a solution the dissolved solid is the solute and the liquid is the solvent. Dissolving is not melting.
Forces, motion and energy
- A force is a push or a pull. Gravity pulls masses toward Earth, friction opposes motion between surfaces, and air and water resistance slow moving objects.
- Balanced forces leave motion unchanged; unbalanced forces change speed or direction. Mass is the amount of matter (kg); weight is the pull of gravity (N).
- Simple machines - lever, pulley, inclined plane, wheel and axle, screw, wedge - change the size or direction of a force but do not create energy.
- Energy is transferred, not used up: food to body to motion; battery to wire to lamp to light and heat.
Light, sound and electricity
Light travels in straight lines, so opaque objects form shadows. Reflection bounces light; refraction bends it on entering a new material. Sound is made by vibration and needs a medium. A circuit must be closed; conductors let current pass and insulators do not. Magnets have north and south poles; like poles repel.
Worked example
A pupil stirs sand and salt into water, then filters the mixture. What is on the filter paper, and how can the salt be recovered?
Reasoning: salt dissolves and sand does not. The filter paper traps the sand as residue; the salty water passes through as filtrate. Evaporating the filtrate leaves salt crystals. Two methods are needed because the parts have different properties.
Traps that cost marks
- Saying a gas has no mass, or that dissolving is melting.
- Confusing mass and weight, or ignoring friction when finding net force.
- Thinking a battery is used up rather than energy being transferred.
- Forgetting that sound cannot travel through a vacuum but light can.
- Drawing a circuit with a gap and expecting the lamp to light.