Learn about the basic principles that govern the physical world around us. Solid understanding of algebra and a basic understanding of trigonometry necessary.
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Community explanations

Calling great explainers of the world! Help us answer frequently asked physics questions by writing clear, deep, engaging explanations. Your explanation may even be selected for an article on Khan Academy (with full credit to you)!

One-dimensional motion

In this tutorial we begin to explore ideas of velocity and acceleration. We do exciting things like throw things off cliffs (far safer on paper than in real life) and see how high a ball will fly in the air.

Two-dimensional motion

You understand velocity and acceleration well in one-dimension. Now we can explore scenarios that are even more fun. With a little bit of trigonometry (you might want to review your basic trig, especially what sin and cos are), we can think about whether a baseball can clear the "green monster" at Fenway Park.

Forces and Newton's laws of motion

This tutorial is the meat of much of classical physics. We think about what a force is and how Newton changed the world's (and possibly your) view of how reality works.

Work and energy

Work and energy. Potential energy. Kinetic energy. Mechanical advantage. Springs and Hooke's law.

Impacts and linear momentum

Linear momentum. Conservation of momentum. Elastic collisions.

Moments, torque, and angular momentum

Thinking about making things rotate. Center of mass, torque, moments and angular velocity.


Classical gravity. How masses attract each other (according to Newton).

Oscillatory motion

Pendulums. Slinkies. You when you have to use the bathroom but it is occupied. These all go back and forth over and over and over again. This tutorial explores this type of motion.


Atmospheric pressure is like an invisible friend who is always squeezing you with a big hug. Learn more about pressure, buoyant force, and flowing fluid so you can appreciate the sometimes invisible, but crucial, effect they have on us and the world around us.


Electricity and magnetism

Electrical circuits are all around us. The computer you're using to read this is full of them! Let's start to study how electrical charges interact.


Mechanical waves and sound

Geometric optics

Light waves

Ask a Physicist! (archived)

Hi everyone, I'm David, and I love physics. Have a physics question/comment? Ask me anything. I'll be checking the comments section every couple hours until Sunday August 2nd at 12:00 PM PST and replying as often as possible. Also, please feel free to answer other people's questions if you know the answer.


Classical gravity. How masses attract each other (according to Newton).
Community Questions
All content in “Gravitation”

Newton's law of gravitation

Why are you sticking to your chair (ignoring the spilled glue)? Why does the earth orbit the sun (or does it)? How high could I throw my dog on the moon? Gravitation defines our everyday life and the structure of the universe. This tutorial will introduce it to you in the Newtonian sense.