Physical Science
What you must understand
Physical science covers matter, motion, forces, and energy. Know that matter has mass and volume, that particles in solids, liquids, and gases differ in spacing and motion, and that a change is physical if the substance stays the same and chemical if a new substance forms. Understand that atoms combine into molecules, and that the total mass is conserved in a closed system. For motion, know that speed is distance divided by time, and that a force is a push or pull that can change an object's motion. Balanced forces mean no change in motion; unbalanced forces cause acceleration. Energy exists in forms such as motion, position, light, sound, heat, and stored chemical energy, and it transfers but is conserved.
Traps to watch for
- Mass versus weight. Mass is the amount of matter and does not change with location; weight depends on gravity.
- Constant speed is still motion. An object moving at steady speed in a straight line has balanced forces.
- Energy transfer versus transformation. A battery to a light bulb is a transformation (chemical to light and heat); a moving ball hitting another is a transfer.
- Melting and dissolving are physical changes, not chemical, because the substance is still the same.
Rule of thumb
For any force question, draw the forces and compare them: equal and opposite means no change in motion; unequal means the motion changes in the direction of the larger force.
Worked example
A student walks 300 meters in 150 seconds. What is the speed? Speed = distance ÷ time = 300 m ÷ 150 s = 2 m/s.