Physical Science: Matter, Motion, and Energy
What the questions target
Washington grade-8 physical science items ask you to explain phenomena using a small set of big ideas: matter is made of particles whose motion and spacing explain properties and phase changes; energy transfers between objects and between forms but is conserved in a closed system; forces change motion, and an object with balanced forces keeps doing what it was doing; and waves carry energy, not matter, with amplitude linked to energy and frequency/wavelength linked inversely.
Traps that cost points
- Confusing weight and mass. Mass (grams/kilograms) is the amount of matter and does not change with location; weight is a force (newtons) that depends on gravity.
- Treating heat and temperature as the same. Temperature measures average particle kinetic energy; heat is energy transferred due to a temperature difference. A large cool object can hold more thermal energy than a small hot one.
- Assuming motion requires a force. Constant velocity means net force is zero. Only acceleration (speeding up, slowing down, turning) requires an unbalanced force.
- Thinking particles expand in a phase change. Particles themselves stay the same size; spacing and freedom of motion change.
- Reading a wave graph carelessly. Amplitude is measured from the center line to a crest, not crest to trough. Doubling frequency halves wavelength if speed is constant.
Rule of thumb
When asked to predict, trace the energy: identify source, path, and final form, then check whether energy left the system as heat or sound. For force questions, draw the arrows first - same size and opposite direction means balanced.
Worked example
A 2 kg cart is pushed with 6 N while 2 N of friction acts backward. Net force = 6 − 2 = 4 N forward, so the cart accelerates forward (a = F/m = 2 m/s²). If the push stops and friction is the only horizontal force, the cart slows but does not instantly reverse - friction opposes motion, it does not create backward travel.