Physics / core

Weight

Also known as: gravitational force, W

definition

The gravitational force acting on an object due to its mass, directed toward the center of a massive body. Distinguishing weight from mass is essential for understanding gravity, designing structures that must support loads, and calculating forces in engineering and space travel.

💡 Intuition

How hard gravity pulls you toward the ground — it changes on different planets.

Core Idea

Weight is a force measured in Newtons — not the same as mass measured in kilograms.

Formal View

Weight is defined as the gravitational force on an object: \vec{W} = m\vec{g}, where m is mass and \vec{g} is the local gravitational field vector directed toward the centre of the gravitating body.

🔬 Example

You weigh less on the Moon (weaker gravity) but your mass stays the same.

🎯 Why It Matters

Distinguishing weight from mass is essential for understanding gravity, designing structures that must support loads, and calculating forces in engineering and space travel.

⚠️ Common Confusion

Scales measure weight (force), but display mass (kg). On the Moon, the scale would show less.

💭 Hint When Stuck

When you see a weight problem, first identify the mass of the object in kilograms and the gravitational acceleration (use g = 9.8 m/s² on Earth). Then substitute into W = mg. Finally, remember that weight is a force measured in newtons, not kilograms.

Related Concepts

Prerequisites

massforcefree fall

How Weight Connects to Other Ideas

To understand weight, you should first be comfortable with mass, force and free fall. Once you have a solid grasp of weight, you can move on to gravity and normal force.

Learn More

Introduction to Physics Concepts — In-depth guide

Compare With Similar Concepts

Mass vs Weight

Go Deeper

Worked Examples

Step-by-step solved problems

Practice Problems

Test your understanding

Formula Explained

Notation, derivation, and common mistakes

Frequently Asked Questions

What is Weight in Physics?

The gravitational force acting on an object due to its mass, directed toward the center of a massive body.

Why is Weight important?

Distinguishing weight from mass is essential for understanding gravity, designing structures that must support loads, and calculating forces in engineering and space travel.

What do students usually get wrong about Weight?

Scales measure weight (force), but display mass (kg). On the Moon, the scale would show less.

What should I learn before Weight?

Before studying Weight, you should understand: mass, force, free fall.

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