Grade 8 Science: Matter, Energy, Force and Motion, Waves, and Electromagnetism
The Science domain of the Georgia Milestones Grade 8 EOG assesses the five Georgia Standards of Excellence for eighth-grade physical science: S8P1 (structure and properties of matter), S8P2 (energy conservation and transformations), S8P3 (force, mass, and motion), S8P4 (mechanical versus electromagnetic waves), and S8P5 (gravity, electricity, and magnetism). Items use data tables, graphs, diagrams, and lab scenarios, so you must apply rules rather than just define terms.
Core rules and concepts
- Matter: density = mass ÷ volume; physical changes alter form but not identity; chemical changes produce new substances; mass is conserved in closed systems.
- Energy: potential energy depends on position, height, or deformation; kinetic energy depends on mass and speed; energy transforms but total energy is conserved; heat moves by conduction, convection, or radiation.
- Force and motion: net force determines acceleration (Newton's second law, F = ma); balanced forces mean zero acceleration, not necessarily zero speed; speed is distance/time, velocity adds direction, and acceleration is change in velocity/time.
- Waves: mechanical waves need a medium; electromagnetic waves travel through a vacuum; frequency and wavelength are inversely related at constant speed; amplitude relates to energy; sound reflects and refracts, and light can be absorbed, reflected, or transmitted.
- Electricity and magnetism: series circuits have one path, parallel circuits have multiple paths; current is the flow of charge, voltage is energy per charge; magnetic fields surround magnets and current-carrying wires; electromagnets depend on current, turns, and core.
Worked example
A 3 kg cart is pushed right with 10 N while friction pulls left with 4 N. Net force = 10 N − 4 N = 6 N right. Acceleration = F_net ÷ m = 6 N ÷ 3 kg = 2 m/s² right. If the cart starts from rest, its velocity after 4 s is v = at = 2 × 4 = 8 m/s right. Reasoning: only unbalanced forces change motion; friction opposes motion but does not cancel the push completely.
Traps that cost marks
- Treating balanced forces as "no motion"; balanced forces allow constant velocity.
- Confusing mass (kg) with weight (N, which depends on gravity).
- Saying energy is "used up" instead of transformed.
- Claiming sound travels in space or that light needs air.
- Mixing series and parallel behavior: one broken series bulb stops all; parallel branches continue.
- Reversing frequency and wavelength.