Physics basics: models, units, and diagrams
Physics is about building simple models for real situations. Start every problem with: What object are we tracking? What forces or energies matter? What stays the same (constants, conserved quantities)? Sketch a quick diagram before you plug numbers in.
Motion in one dimension
Displacement is where you end minus where you started (a vector idea on a line: + or −). Average speed uses total distance; average velocity uses displacement over time. On constant-acceleration problems, the “kinematic” equations your teacher gives are just shortcuts—know what each symbol means before you memorize.
Newton’s three laws (how forces actually behave)
- First law (inertia): Velocity stays constant unless a net outside force shows up.
- Second law: Fnet = ma links net force, mass, and acceleration. Draw free-body vectors so you only add the pieces that belong on that object.
- Third law: Forces come in pairs on different objects—action/reaction never cancel on the same object.
Work, energy, and power
Work transfers energy through a force acting through a displacement (with careful attention to angles). Kinetic energy is ½mv² for speeds well below the speed of light in intro courses. Gravitational potential energy near Earth is often mgh with a consistent zero height.
Energy bar charts help: track forms in vs. forms out, including “lost” mechanical energy to heat when friction is in the story.
Momentum and collisions
Momentum p = mv is useful when forces are messy but collision times are short. In a closed system with no outside impulse, total momentum before equals total momentum after. Elastic collisions keep kinetic energy in the bookkeeping; inelastic ones do not—some kinetic energy becomes thermal or sound.
Heat and temperature (intro)
Temperature tracks average particle motion in a simple model; heat is energy moving because of a temperature difference. Specific heat problems are often “energy in = mass × specific heat × ΔT” when phase change is not happening. Save the full thermodynamics laws for the unit that names them—match the wording your course uses.
Quick review checklist
Run this on paper the night before an assessment—short answers, no peeking.
- Vocabulary: Five terms, defined in your own words.
- One strong example: Problem, diagram, quote+context, or map label your rubric would accept.
- Classic trap: What mistake shows up on every test—and what rule stops it?
- Connection: One sentence linking this topic to another unit from the same course.