Gravity: Weight vs Mass
Mass and weight are often confused in everyday language, but they are fundamentally different quantities. Mass is the amount of matter in an object; weight is the gravitational force acting on that mass.
What You Need to Know
Key Concept Diagram
Mass is the amount of matter in an object, measured in kilograms; it does not change with location
Weight is the force of gravity on an object, measured in Newtons: W = m x g
On Earth, g = 9.8 m/s^2; on the Moon g = 1.6 m/s^2, so the same object weighs less there
Gravity is a universal attractive force between all objects with mass
Key Vocabulary
Mass
The amount of matter in an object; measured in kilograms (kg); constant everywhere
Weight
The force of gravity on an object; measured in Newtons (N); varies with location
Gravitational field strength
The acceleration due to gravity (g); 9.8 m/s^2 on Earth's surface
Newton
The SI unit of force; 1 N = the force needed to accelerate 1 kg at 1 m/s^2
Knowledge Check
Select the correct answer for each question. Click "Check Answer" to see if you are right.
Question 1
An astronaut has a mass of 70 kg on Earth. What is their mass on the Moon?
Question 2
Calculate the weight of a 5 kg object on Earth. (g = 9.8 m/s^2)
Question 3
Why do astronauts float in the International Space Station?
Key Concepts Summary
- ●Mass is the amount of matter in an object, measured in kilograms; it does not change with location
- ●Weight is the force of gravity on an object, measured in Newtons: W = m x g
- ●On Earth, g = 9.8 m/s^2; on the Moon g = 1.6 m/s^2, so the same object weighs less there
- ●Gravity is a universal attractive force between all objects with mass