Kinematics: Describing Motion With Velocity & Acceleration

Before physics can explain why things move, it needs a precise way to describe how they move. That's kinematics. With just three quantities — where something is (position), how fast and which way it's going (velocity), and how quickly that's changing (acceleration) — you can fully describe any motion. And motion graphs let you see all of it at once, which is exactly what ACT Science physics passages ask you to read.

This guide covers the core quantities, motion graphs, and the kinematic equations, with worked and practice questions matched to the level seen in ACT Science and physics at Northside Tutoring.

Why Kinematics Matters

Kinematics is the foundation of physics and a common ACT Science topic, often presented as motion graphs or data tables. The reasoning blends physics with the graph-reading skills the section rewards. (The SAT has no science section.)

The Core Quantities

Three quantities describe motion: position (where an object is), velocity (how fast and in what direction it moves), and acceleration (how fast the velocity changes). Distance and displacement differ too: distance is total path length, while displacement is the straight-line change in position, including direction.

Speed vs. Velocity

Speed is how fast something moves (a number, like 60 mph). Velocity adds direction (60 mph north). That distinction matters: a car going around a circular track at a steady speed still has changing velocity, because its direction keeps changing.

Acceleration

Acceleration is the rate at which velocity changes — speeding up, slowing down, or changing direction:

Because velocity includes direction, slowing down is negative acceleration, and even turning at constant speed counts as acceleration.

Reading Motion Graphs

The Kinematic Equations

For motion with constant acceleration, three equations relate the quantities:

Equation	Use it to find
v = v₀ + at	final velocity
d = v₀t + ½at²	displacement
v² = v₀² + 2ad	velocity without time

(Here v₀ is the starting velocity, v the final, a the acceleration, t time, d displacement.)

Where You'll See This — Test by Test

Kinematics supports ACT Science physics passages and motion graphs; the SAT has no science section and the SSAT doesn't test it. It's core high-school and AP Physics.

Watch the Lesson

Sometimes a diagram needs a voice. In the short video below, one of our Northside tutors walks through the core idea and works through test-style problems in real time.

Worked Example Problems

These problems are calibrated to the difficulty you'll actually see on test day. Try each one before opening the solution.

Common Mistakes to Avoid

Practice Problems — You Try

Three problems below. Work each before checking the solution.

The Northside Method — How We Teach This 1-on-1

Reading a blog is a great starting point. But there's a meaningful gap between understanding a concept and reflexively applying it under timed conditions. That gap is exactly what our tutors close.

Every Northside student works through a four-step framework:

1. Assessment. We diagnose which specific skills are slowing your student down — not just whether they "get it" in the abstract.
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4. Data-driven adjustment. Every session ends with a check on whether the student's accuracy and speed are moving in the right direction.

And if a student meets all eligibility requirements but doesn't hit the defined score improvement? We provide 5 additional hours of cohort learning at no cost. That's the Northside guarantee — built on 25 years of measured outcomes.