Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Gravity is a non-contact force that pulls objects toward each other. On Earth, it pulls everything toward the center of the planet.
Mass is the amount of matter in an object and is measured in kilograms (). It does not change regardless of where the object is in the universe.
Weight is the force of gravity acting on an object's mass and is measured in Newtons ().
The gravitational field strength () on Earth is approximately , often rounded to for introductory physics.
The Moon has less mass than Earth, so its gravity is weaker. Gravity on the Moon is about of the gravity on Earth.
Objects fall toward the ground because of gravity. In a vacuum (no air), all objects fall at the same rate regardless of their mass.
📐Formulae
💡Examples
Problem 1:
A school bag has a mass of . Calculate its weight on Earth using .
Solution:
Explanation:
To find the weight, we multiply the mass () by the Earth's gravitational field strength ().
Problem 2:
An astronaut weighs on Earth. If the gravity on the Moon is of Earth's gravity, what is the astronaut's weight on the Moon?
Solution:
Explanation:
Since the Moon's gravity is one-sixth of Earth's, we divide the weight on Earth by . Note that the astronaut's mass stays the same.
Problem 3:
If a rock weighs on Earth (where ), what is its mass?
Solution:
Explanation:
Using the formula , we divide the weight by the gravitational field strength to find the mass.