An astronaut lands on a moon that has one-twentieth the mass of Earth and two-fifths the radius....

After completing this lesson, you will be able to explain what energy is and what we mean when we say energy is 'conserved,' and give some examples of conversions between different types of energy.

How do we use physics to answer questions about motion? One way is with kinematics, and in this lesson we'll examine several kinematics equations and how to use them.

Intensity in physics is a fundamental concept that scientists and engineers often use. Learn what the definition of intensity is and how to measure it in this lesson.

After completing this lesson, you will be able to explain what an electric circuit it, how energy transfers in a circuit, and how circuits relate to the conservation of energy. A short quiz will follow.

Does gravity have you down? Well, you are not alone. Gravity is the force that pulls objects with mass toward each other. It is what holds you to the earth. Learn how the strength of gravity is affected by mass and distance.

This lesson is about wind energy. In this lesson we'll go over what wind energy is and how it makes electricity, and the pros and cons of using this type of energy source.

Time slows down for objects in motion. While this effect is not noticeable in everyday experience, it becomes apparent at speeds approaching the speed of light. This lesson defines this phenomenon as time dilation. Examples are used to help explain how time is relative to speed.

This lesson defines what a gravitational field is and some practical examples encountered in the real world. We also develop the equations governing the gravitational field and explain what the units of measurement mean.

Plane shapes are all around us, but how do we know what shapes are plane shapes? In this lesson, you will learn what plane shapes are and explore their different types and properties.

After watching this video, you will be able to explain what sun-synchronous and geostationary orbits are and why they are useful. A short quiz will follow.

Work and energy are closely related in physics. In this lesson, you'll learn what that relationship is as well as how we can apply it to various situations.

You probably have an idea of what gravity is, but did you know that you, right now, are actually pulling on every other object in the universe? Find out more about the gravitational force and learn an equation to calculate its pull on other objects.

Very few single chemical elements are encountered in everyday life. In this lesson, you will learn about chemical compounds through some examples to gain a better understanding of what they are and how they form.

Learn to identify the different sizes and colors of stars and how they relate to the star life cycle. In this lesson, we'll talk about spectral classification, how many stars there are of each type and the approximate color of the different classes of stars.

A lever is one of the most common tools we use to help us lift things beyond our strength limit. Learn about the components of a lever, find out about three different lever classes, and see some common examples of each.

What keeps a roller coaster in a loop? Learn about centripetal force, what causes a centripetal force, and how to calculate it. Complete a quiz to test your knowledge.