---
title: "Electrostatic Force — AP Physics 2 Definition & Exam Guide"
description: "The electrostatic force is the attraction or repulsion between charges, found with Coulomb's law. Learn how AP Physics 2 tests it in free-body diagrams."
canonical: "https://fiveable.me/ap-physics-2-revised/key-terms/electrostatic-force"
type: "key-term"
subject: "AP Physics 2"
unit: "Unit 3"
---

# Electrostatic Force — AP Physics 2 Definition & Exam Guide

## Definition

The electrostatic force is the attractive or repulsive force between charged objects, calculated with Coulomb's law (F = kq₁q₂/r²); in AP Physics 2 it appears as a vector in free-body diagrams, attractive for opposite charges and repulsive for like charges.

## What It Is

The electrostatic force is the push or pull between objects that carry [electric charge](/ap-physics-2-revised/unit-10/1-electric-charge-and-electric-force/study-guide/E6OYkOGeroCXwgw1 "fv-autolink"). Opposite charges attract, like charges repel, and the strength of the force comes from **[Coulomb's law](/ap-physics-2-revised/key-terms/coulombs-law "fv-autolink")**: F = kq₁q₂/r². The force grows with bigger charges and shrinks fast as the charges move apart, since it falls off with the square of the distance. Double the separation and the force drops to one quarter.

In [AP Physics 2](/ap-physics-2-revised "fv-autolink"), the electrostatic force isn't a new kind of physics so much as a new force you add to your Unit 1-style toolbox. It obeys Newton's third law (the proton pulls on the electron exactly as hard as the electron pulls on the proton), it's a vector, and it goes on a free-body diagram just like tension or friction. Topic 3.7 is exactly that move: take a charged object, draw every force on it including the electrostatic one, and apply Newton's second law. A helpful mental model is that Coulomb's law is gravity's twin with two big differences. Charge replaces mass, and the force can repel as well as attract.

## Why It Matters

This term lives in **Topic 3.7 (Electric Forces and Free-Body Diagrams)** in the [Electric Force, Field, and Potential](/ap-physics-2-revised/unit-10 "fv-autolink") unit of AP Physics 2. It's the bridge between mechanics and electricity. Everything you learned about free-body diagrams, equilibrium, and [Newton's second law](/ap-physics-2-revised/key-terms/newtons-second-law "fv-autolink") now gets reused with a charged object instead of a block on a ramp. Classic setups include a charged ball hanging from a string near another charge (electrostatic force plus tension plus gravity), an electron orbiting a proton (electrostatic force as the centripetal force), and charges pinned in a line or triangle where you add Coulomb forces as vectors. If you can't draw the electrostatic force correctly on a diagram, the whole field-and-potential chain that follows in the unit falls apart, because the electric field is literally defined from this force.

## Connections

### [Coulomb's Law (Unit 3)](/ap-physics-2-revised/key-terms/coulombs-law)

Coulomb's law is the equation; the electrostatic force is the thing it calculates. On the exam they're nearly interchangeable, but Coulomb's law gives you the magnitude, and you supply the direction by asking whether the charges attract or repel.

### Electric Field (Unit 3)

The electric field is defined as electrostatic force per unit charge (E = F/q). Once you know the field at a point, the force on any charge placed there is just F = qE. The field is the cause-at-a-distance; the force is what the charge actually feels.

### [Gravitational Force (Units 1 and 3)](/ap-physics-2-revised/key-terms/gravitational-force)

Coulomb's law and Newton's law of gravitation have the same 1/r² shape, so problem-solving strategies transfer directly. The twist is that gravity only attracts while the electrostatic force can repel, and at the atomic scale the electrostatic force dwarfs gravity. That size gap is why exam problems tell you to ignore gravity between subatomic particles.

### Point Charges (Unit 3)

Coulomb's law is written for point charges, objects small enough that all their charge sits at one location. When a problem has multiple point charges, you find the electrostatic force from each one separately and add them as vectors ([superposition](/ap-physics-2-revised/key-terms/superposition "fv-autolink")).

## On the AP Exam

Multiple-choice questions love ratio reasoning. If the distance doubles, what happens to the force? If both charges triple? You should be able to answer those without a calculator using the kq₁q₂/r² structure. Free-response questions typically embed the electrostatic force inside a Newton's-laws problem. A released 2022 free-response question modeled a hydrogen atom as an electron in a circular orbit around a proton and explicitly told you the gravitational force was negligible compared to the electrostatic force. That's the signature move: set the electrostatic force equal to the net centripetal force (kq²/r² = mv²/r) and solve. Also expect free-body diagram tasks where you must draw the electrostatic force with the correct direction (along the line between the charges, toward for attraction, away for repulsion) and correct relative length, plus Newton's third law checks confirming the forces on each charge are equal in magnitude.

## Electrostatic Force vs Electric Field

The electrostatic force is what a charge actually experiences, measured in newtons. The electric field is the force per unit charge that exists at a point in space whether or not anything is there to feel it, measured in N/C. They're linked by F = qE. A common trap is direction: the field points the way a positive test charge would be pushed, so a negative charge feels a force opposite to the field.

## Key Takeaways

- The electrostatic force between two point charges has magnitude F = kq₁q₂/r², attracting opposite charges and repelling like charges.
- It's an inverse-square force, so doubling the distance between charges cuts the force to one quarter.
- Electrostatic forces obey Newton's third law, meaning both charges feel forces of equal magnitude even if their charges are very different.
- On free-body diagrams, treat the electrostatic force like any other force vector and combine it with gravity, tension, or normal forces using Newton's second law.
- Between subatomic particles, the electrostatic force is enormously stronger than gravity, which is why exam problems about atoms tell you to ignore gravitational attraction.
- With multiple charges, find the force from each charge separately and add them as vectors using superposition.

## FAQs

### What is the electrostatic force in AP Physics 2?

It's the attractive or repulsive force between charged objects, with magnitude given by Coulomb's law, F = kq₁q₂/r². It shows up in Topic 3.7, where you put it on free-body diagrams alongside forces like gravity and tension.

### Is the electrostatic force the same as the electric field?

No. The force (in newtons) is what a specific charge feels, while the field (in N/C) describes the force per unit charge at a point in space. They're connected by F = qE, and a [negative charge](/ap-physics-2-revised/key-terms/negative-charge "fv-autolink") feels a force opposite to the field direction.

### How is the electrostatic force different from gravity?

Both follow an inverse-square law, but gravity depends on mass and only attracts, while the electrostatic force depends on charge and can attract or repel. Between an [electron](/ap-physics-2-revised/unit-15/2-the-bohr-model-of-atomic-structure/study-guide/gzEFr1ron8hpACPx "fv-autolink") and a proton, the electrostatic force is so much stronger that the AP exam tells you to treat gravity as negligible.

### Can the electrostatic force be repulsive?

Yes. Two charges with the same sign (both positive or both negative) repel each other, while opposite signs attract. Coulomb's law gives the magnitude either way; you assign the direction from the signs of the charges.

### What happens to the electrostatic force if you double the distance between two charges?

It drops to one quarter of its original value, because the force depends on 1/r². This ratio-style reasoning is one of the most common ways multiple-choice questions test Coulomb's law.

## Related Study Guides

- [3.7 Electric Forces and Free-Body Diagrams](/ap-physics-2-revised/unit-3/electric-forces-free-body-diagrams/study-guide/w5TVC61CqiWuO8C9uhGK)

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