Biology
How living things work.
- Cells and organelles
- Photosynthesis
- Genetics basics
Learn it once, remember it for the exam.
Short lessons and revision guides in science, maths, English and computing, written for high-school and first-year college students.
Browse subjectsSubjects
Each subject is split into short topics you can finish in one sitting.
Chemistry
Matter, bonds and reactions.
- The periodic table
- Balancing equations
- Acids and bases
Physics
Forces, energy and waves.
- Newton’s laws
- Electric circuits
- Light and sound
Mathematics
From algebra to calculus.
- Linear equations
- Trigonometry
- Differentiation
English
Reading, writing and grammar.
- Essay structure
- Comprehension
- Punctuation
Computing
How computers and the web work.
- Binary and data
- Intro to Python
- How the internet works
Latest lessons
Start with one of these.
- Photosynthesis explainedBiology
- Pythagoras’ theoremMathematics
- Newton’s three laws of motionPhysics
Quick reference
Three formulas students look up most often.
v = d ÷ tSpeed equals distance divided by time
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂Photosynthesis, balanced
a² + b² = c²Pythagoras’ theorem for right triangles
Questions
Is the content free?
Yes. All lessons and revision guides are free to read.
Which levels do you cover?
High-school and first-year college material.
How often are lessons added?
New topics are added every few weeks.