AP Physics8 min read

5 Physics Misconceptions That Trip Up AP Students

March 8, 2026

After years of tutoring AP Physics students, I've noticed the same misconceptions appearing again and again. These aren't signs of poor understanding — they're actually natural intuitions that happen to be wrong. Let's clear them up.

1. "Heavier objects fall faster"

In a vacuum, all objects fall at the same rate regardless of mass. Galileo demonstrated this centuries ago. Air resistance is what makes a feather fall slower than a hammer — not its mass. On the Moon (no atmosphere), they fall identically.

Free Fall (no air resistance)

a = g = 9.8 \text{ m/s}^2

Same for ALL objects!

2. "Newton's Third Law pairs can cancel out"

Action-reaction pairs act on DIFFERENT objects, so they never cancel. When you push a wall, the wall pushes back on you. These forces act on different bodies and don't combine. This is the #1 source of errors in free body diagrams.

Newton's Third Law

\vec{F}_{A \to B} = -\vec{F}_{B \to A}

Equal magnitude, opposite direction, different objects

3. "Objects in circular motion are pushed outward"

There is no outward "centrifugal force." Objects in circular motion are accelerating INWARD toward the center — that's centripetal acceleration. What you feel as being "pushed outward" in a car turn is actually your body wanting to continue in a straight line.

Centripetal Acceleration

a_c = \frac{v^2}{r}

Always points toward the center

4. "Current gets used up in a circuit"

Current is the same everywhere in a series circuit. What gets "used up" is electrical potential energy (voltage drops). Electrons flow in a complete loop — they don't disappear inside a light bulb.

Ohm's Law & Power

V = IR \quad\quad P = IV

Current I is constant; voltage V drops across resistors

5. "Velocity and acceleration are always in the same direction"

When you throw a ball upward, its velocity is upward but acceleration (gravity) is downward — from the moment it leaves your hand. Objects can slow down (decelerate) when velocity and acceleration point opposite ways.

Kinematics

v = v_0 + at

If $a$ and $v_0$ have opposite signs, $v$ decreases!

💡 How to fix misconceptions

Don't just memorize the correct answer — understand WHY the misconception feels true. Your brain built that intuition from real experiences. Reconcile the physics with those experiences.

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