Physical Sciences: Matter, Forces, Energy, and Electricity
What to know
Matter has mass and takes up space. It exists as solids, liquids, and gases, and changes state when heat is added or removed (melting, freezing, evaporation, condensation). Physical changes alter size, shape, or state without making a new substance; chemical changes produce a new substance with different properties (burning, rusting, baking). Mixtures can be separated by physical means; a solution is a mixture in which one substance dissolves evenly in another.
Forces are pushes or pulls. Gravity pulls objects toward Earth, friction opposes motion between surfaces, and magnetism acts at a distance on certain metals. Unbalanced forces change motion; balanced forces do not. Simple machines (lever, pulley, wheel and axle, inclined plane, wedge, screw) make work easier by changing the direction or size of a force.
Energy comes in forms - light, sound, heat, electrical, mechanical, chemical - and is transferred, not used up. In a circuit, current flows only through a closed loop; conductors (metals) allow flow, insulators (rubber, plastic) block it. Light travels in straight lines and reflects off surfaces; sound travels as vibrations through a medium.
Traps
- Calling dissolving a chemical change - it is physical.
- Confusing mass with weight; mass stays the same when location changes.
- Thinking a larger object is always heavier - density matters.
- Believing energy disappears when a device stops; it transfers to other forms.
- Assuming all metals are magnetic - only iron, nickel, and cobalt are strongly attracted.
Worked example
Tearing paper = physical (still paper). Burning paper = chemical (ash, smoke, heat - new substances).