⚡ Physics: Motion, Energy and Waves

Part 1 of 7 — Physics on the ASVAB: Units and Metric Prefixes

Topic Overview

Where Physics Shows Up

General Science (GS) is the first subtest on the CAT-ASVAB. You get 15 scored questions in 12 minutes, which works out to about 48 seconds per question. The official description is "knowledge of physical and biological sciences," and physical science (force and motion, energy, fluids, atoms, chemistry) is one of its three big areas, next to life science and earth and space science.

The physics questions are not long calculations. They are mostly "do you know this fact or idea?" questions, plus some one- or two-step problems with friendly numbers. No calculator is allowed, so the numbers are chosen to work out by hand.

Why GS matters: GS does not count toward your AFQT, but it feeds job line scores. The Air Force E (Electronics) composite is GS + AR + MK + EI, and the Navy and Marine Corps EL composites use the same four subtests. Electronics, nuclear and many technical jobs care about this score.

What You Will Learn in This Lesson

Physics on the ASVAB comes down to a short list of ideas: how things move, why they move (forces), how energy changes form, how waves carry sound and light, and how charges and magnets push and pull. This part starts with the toolkit every one of those questions uses: units.

⚡ Physics: Motion, Energy and Waves

Part 2 of 7 — Motion, Forces and Newton's Laws

Describing Motion

The distance triangle. Speed, distance and time are linked by $d = s \times t$. Cover the one you want:

• distance = speed × time
• speed = distance ÷ time
• time = distance ÷ speed

Example 1. A convoy drives at 50 mph for 3 hours. Distance = 50 × 3 = 150 miles.

Example 2. A truck covers 180 miles at 60 mph. Time = 180 ÷ 60 = 3 hours.

Example 3. A car speeds up from 0 to 20 m/s in 5 seconds. Acceleration = 20 ÷ 5 = 4 m/s²: its speed grows by 4 m/s every second.

Key Fact: Acceleration means any change in velocity: speeding up, slowing down, or changing direction. A car going around a curve at a steady 30 mph is accelerating, because its direction changes.

Reading a distance–time graph

On a graph of distance against time, the steepness (slope) is the speed. A steeper line means faster, and a flat line means the object is stopped.

⚡ Physics: Motion, Energy and Waves

Part 3 of 7 — Work, Energy, Power and Heat

Work

In physics, work is done only when a force moves something in the direction of the force:

$W = F \times d$

Force in newtons times distance in meters gives work in joules (J).

Example 1. You push a crate with 50 N of force for 4 m. Work = 50 × 4 = 200 J.

Example 2. You hold a heavy box perfectly still for a minute. Your arms get tired, but the box does not move, so the work done on the box is zero.

Two kinds of mechanical energy

Example 3. A 2 kg ball moving at 3 m/s has $KE = \frac{1}{2} \times 2 \times 3^2 = 9$ J.

Example 4. A 5 kg box on a shelf 2 m high has $PE = 5 \times 10 \times 2 = 100$ J (using $g \approx 10$ m/s² to keep the numbers friendly).

Key Fact: Double the speed and the kinetic energy becomes four times as large, because speed is squared. That is why a car at 60 mph needs about four times the braking distance it needs at 30 mph.

⚡ Physics: Motion, Energy and Waves

Part 4 of 7 — Waves, Sound and Light

Anatomy of a Wave

A wave carries energy from place to place without carrying matter along with it. A cork on a pond bobs up and down as waves pass, but it does not travel across the pond.

The wave equation

$v = f\lambda$

Wave speed = frequency × wavelength.

Example 1. A wave has a frequency of 5 Hz and a wavelength of 2 m. Speed = 5 × 2 = 10 m/s.

Example 2. A wave travels at 12 m/s with a wavelength of 3 m. Frequency = 12 ÷ 3 = 4 Hz, and its period is 1/4 second.

Key Fact: For waves moving at the same speed, higher frequency means shorter wavelength. Frequency and wavelength trade off.

Two kinds of waves

⚡ Physics: Motion, Energy and Waves

Part 5 of 7 — Electricity and Magnetism Basics

Electric Charge

All matter is made of atoms with positive protons and negative electrons. Normally the charges balance. Rub two materials together (a balloon on your hair, socks on carpet) and electrons move from one to the other: one object becomes negative (extra electrons), the other positive (missing electrons). That built-up charge is static electricity.

Key Fact: Only electrons move when objects become charged. Protons stay locked in the nucleus.

Conductors and Insulators

That is why wires are copper on the inside and covered in plastic or rubber on the outside.

Three words you need

They are linked by Ohm's law, $V = IR$. Working with circuits (series, parallel, power in a circuit) belongs to the Electronics Information subtest; for GS, know the three words, their units, and that a battery's direct current (DC) flows one way while wall outlets supply alternating current (AC), which reverses direction many times a second.

⚡ Physics: Motion, Energy and Waves

Part 6 of 7 — Test Strategy and Common Traps

Your Clock on GS

Most physics questions are recall questions you can answer in 15 to 20 seconds if you know the fact. That banks time for the ones that need a quick calculation.

Time budget for a physics question

1. Read the last line first. What is being asked for: a unit, a direction, a number?
2. Name the idea. "This is Newton's third law" or "this is $v = f\lambda$." Most GS physics needs only one formula.
3. Estimate before you compute. Friendly numbers are the rule (no calculator is allowed). If your answer is ugly, recheck.
4. Eliminate. Cross out choices with the wrong unit or the wrong direction first.

Running short on time

On the CAT, unfinished questions at the time limit are scored as if you had guessed at random, and the official guidance warns that a string of wrong answers near the end of a subtest is penalized heavily. Since GS is mostly recall, you rarely run short; if you do, keep reading and answering each question for real rather than clicking randomly.

⚡ Physics: Motion, Energy and Waves

Part 7 of 7 — Mixed Mastery Set

How This Set Works

These questions mix every part of the lesson, in the style and difficulty range of the GS subtest: mostly quick recall, a few one- or two-step calculations, and a couple of harder "which idea applies?" questions. Give yourself about 48 seconds per question, the CAT pace.

Tip: After each question, read the explanation even when you are right. Explanations show the fastest route.