Learn science using videos, articles, and TEKS-aligned practice exercises. Review the fundamentals of matter and energy, forces and motion, Earth's systems and processes, living organisms and …

Created by experts, Khan Academy’s library of trusted, standards-aligned practice and lessons covers math K-12 through early college, grammar, science, history, AP®, SAT®, and more.

Unit 1: Intro to biology Welcome to biology! The science of biology Water and life

The scientific method is used in all sciences—including chemistry, physics, geology, and psychology. The scientists in these fields ask different questions and perform different tests. However, they use …

3:57 Conventional current direction Getting started Article Preparing to study electrical engineering on Khan Academy Getting started

This unit is part of the Biology archive. Browse videos and articles by topic. For our most up-to-date, mastery-enabled courses, check out [High School Biology] …

The scientific method begins with an observation, which leads the scientist to ask a question. They then come up with a hypothesis, a testable explanation that addresses the question.

可汗学院提供免费的物理学课程，涵盖基础概念和进阶主题，帮助学习者深入理解物理世界。

Sal and Jay cover topics covered in college organic chemistry course. Basic understanding of basic high school or college chemistry assumed (although there is some review).

Circuit analysis is the process of finding all the currents and voltages in a network of connected components. We look at the basic elements used to build circuits, and find out what happens when …