https://edubun.com/en/Free lessons: 113 courses in 36 subjects, from math and science to languages, music and coding, with short explanations, 3D models and practice questions. New courses are added every day.enMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/algebra/expressions/https://edubun.com/en/algebra/expressions/Six units on algebraic expressions: letters for numbers and how to turn words into expressions, evaluating with the order of operations, terms and like terMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/algebra/functions/https://edubun.com/en/algebra/functions/Six units on functions: what makes a rule a function, domain and range, reading a graph, shifting and stretching graphs, putting one function inside anotheMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/algebra/graphs/https://edubun.com/en/algebra/graphs/Six units on the coordinate plane and straight lines: plotting ordered pairs, graphing an equation from a table or its intercepts, slope as rise over run, Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/algebra/linear-equations/https://edubun.com/en/algebra/linear-equations/Eight units on equations such as 3x + 5 = 20: what a solution is, the four properties of equality, equations with the variable on both sides, the general sMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/algebra/quadratics/https://edubun.com/en/algebra/quadratics/Six units on quadratic functions and equations: the parabola, vertex form, factoring, the quadratic formula, the discriminant and a thrown ball. A functionMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/algebra/quadratics/quadratic-formula/https://edubun.com/en/algebra/quadratics/quadratic-formula/Al-Khwarizmi solved x² + 10x = 39 around 800 by completing a square. The quadratic formula is the same steps done once for every a, b and c.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/arithmetic/decimals-percent/https://edubun.com/en/arithmetic/decimals-percent/Seven units on decimals and percent for everyday arithmetic: place value, adding and multiplying decimals, switching between fractions, decimals and percenMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/arithmetic/decimals-percent/percent-change/https://edubun.com/en/arithmetic/decimals-percent/percent-change/A price that goes up 20% and then down 20% ends 4% lower than where it started.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/arithmetic/fractions/https://edubun.com/en/arithmetic/fractions/Ten units that take fractions from equal parts of one whole to dividing one fraction by another. Each unit has diagrams, a fraction bar to shade, worked exMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/arithmetic/fractions/fractions-on-a-number-line/https://edubun.com/en/arithmetic/fractions/fractions-on-a-number-line/3/4 sits three quarters of the way from 0 to 1, and 7/4 sits the same distance past 1.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/arithmetic/ratio/https://edubun.com/en/arithmetic/ratio/Six units on comparing quantities: ratios, unit rates and unit prices, proportions, map scales, scaling recipes, and speed. Each unit has diagrams, worked Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/cells/https://edubun.com/en/biology/cells/Every living thing is built from cells, and most of them are far too small to see. This course starts with the people who first saw cells, measures them inMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/evolution/https://edubun.com/en/biology/evolution/Run a natural selection lab: made-up beetles on bark of different shades, with sliders for selection pressure and mutation rate and a bar chart for each geMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/https://edubun.com/en/biology/genetics/A short stretch of human DNA in 3D: turn the double helix, unzip it, watch it copy itself and watch a gene being read. The course goes from genes and base Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/base-pairs/https://edubun.com/en/biology/genetics/base-pairs/Each step of the DNA ladder rises 0.34 nm, and ten steps make one full turn of 3.4 nm.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/chromosomes/https://edubun.com/en/biology/genetics/chromosomes/Stretched end to end, the DNA in a single human cell would reach about 2 meters.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/dna-technology/https://edubun.com/en/biology/genetics/dna-technology/Thirty rounds of PCR turn one piece of DNA into about a billion copies.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/genes-and-dna/https://edubun.com/en/biology/genetics/genes-and-dna/One human chromosome set holds about 3 billion DNA base pairs; about 1 percent of its sequence codes for proteins.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/mendel/https://edubun.com/en/biology/genetics/mendel/In 1865 a monk in Brno reported crosses of nearly 30,000 pea plants, and the same 3 to 1 ratio kept turning up.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/mutations/https://edubun.com/en/biology/genetics/mutations/Change one A to a T in the 20th base of the beta-globin gene, and the result is the variant behind sickle cell disease.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/genetics/punnett-squares/https://edubun.com/en/biology/genetics/punnett-squares/A 2 by 2 grid predicts that two Yy pea plants give green seeds one time in four.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/microbes/https://edubun.com/en/biology/microbes/In 1676 Antonie van Leeuwenhoek told the Royal Society that a single drop of pepper water held upwards of a million living creatures. Meet bacteria, archaeMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/microbes/bacteria/https://edubun.com/en/biology/microbes/bacteria/Under good laboratory conditions one E. coli cell can become two in about 20 minutes.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/microbes/bacterial-growth/https://edubun.com/en/biology/microbes/bacterial-growth/One cell that divides every 30 minutes would, with unlimited food, become 281,474,976,710,656 cells in 24 hours.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/microbes/fungi-and-protists/https://edubun.com/en/biology/microbes/fungi-and-protists/In 1928 Alexander Fleming noticed that a mold growing on one of his culture plates at St Mary’s Hospital in London had stopped the bacteria around it.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/microbes/germ-theory/https://edubun.com/en/biology/microbes/germ-theory/In 1668 Francesco Redi put meat in six jars, left two open, covered two with gauze and sealed two, and only the open jars grew maggots in the meat.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/microbes/viruses/https://edubun.com/en/biology/microbes/viruses/In 1892 Dmitri Ivanovski passed sap from sick tobacco plants through a porcelain filter that stopped all bacteria, and the sap could still make plants sickMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/microbes/what-are-microbes/https://edubun.com/en/biology/microbes/what-are-microbes/You can just see something about 100 micrometres wide with the naked eye; a typical bacterium is about one hundredth of that.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/plants/https://edubun.com/en/biology/plants/A 5-pound willow shoot grew into a 169-pound tree in five years while its soil lost about 2 ounces. Find out where that mass came from, change light, CO₂ aMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/biology/plants/flowers-and-seeds/https://edubun.com/en/biology/plants/flowers-and-seeds/At least 25,000 species of orchid have been named, and some of them get pollinated by tricking wasps.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/calculus/derivatives/https://edubun.com/en/calculus/derivatives/Six units on the derivative, the slope of a curve at a single point. You define it as a limit of secant slopes, read it as a new function with its own grapMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/calculus/integrals/https://edubun.com/en/calculus/integrals/Five units on the second big idea of calculus: area under a curve, built from thin rectangles. You add rectangles with sigma notation, compare left, right Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/calculus/limits/https://edubun.com/en/calculus/limits/Five units on the idea that holds calculus together. You start with the two questions that led to calculus, the slope of a curve and the area under it, theMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/acids-bases/https://edubun.com/en/chemistry/acids-bases/Lemon juice, stomach acid, baking soda and drain cleaner sit at different points on one scale. Slide along the pH scale and watch four indicators change coMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/acids-bases/acids-and-bases/https://edubun.com/en/chemistry/acids-bases/acids-and-bases/In pure water at 25 °C only about two molecules in every billion have split into ions, and that tiny amount is where acids and bases begin.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/acids-bases/indicators/https://edubun.com/en/chemistry/acids-bases/indicators/Phenolphthalein stays colourless in any solution below pH 8.3 and turns pink above it.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/acids-bases/neutralization/https://edubun.com/en/chemistry/acids-bases/neutralization/Add 0.100 M sodium hydroxide to 25.00 mL of 0.100 M hydrochloric acid and the pH jumps from 3.70 to 10.30 between 24.9 mL and 25.1 mL.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/acids-bases/ph-scale/https://edubun.com/en/chemistry/acids-bases/ph-scale/Vinegar at pH 2.4 has about 40,000 times more hydronium ions per litre than pure water at pH 7.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/acids-bases/strong-and-weak/https://edubun.com/en/chemistry/acids-bases/strong-and-weak/At 0.100 M, hydrochloric acid is fully ionized and has pH 1.00, while acetic acid has given up only 1.3% of its protons and has pH 2.87.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/atoms/https://edubun.com/en/chemistry/atoms/Everything you can touch is made of atoms. The three particle types used to describe atoms are protons, neutrons and electrons; ordinary hydrogen has no neMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/atoms/inside-an-atom/https://edubun.com/en/chemistry/atoms/inside-an-atom/If an atom were the size of a football stadium, its nucleus would be about the size of a pea in the middle.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/bonds/https://edubun.com/en/chemistry/bonds/Why does salt form cubes, why is water bent, and why can copper be drawn into wire? Turn 14 molecules in 3D, switch between ball-and-stick and space-fillinMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/bonds/metallic-bonds/https://edubun.com/en/chemistry/bonds/metallic-bonds/Gold can be beaten into leaf so thin that light passes through it. Metallic bonds bend instead of breaking.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/bonds/reading-formulas/https://edubun.com/en/chemistry/bonds/reading-formulas/Ethanol and dimethyl ether both have the formula C₂H₆O, yet one is in drinks and the other is a gas used as a fuel.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/matter/https://edubun.com/en/chemistry/matter/Why does ice float, why does water boil at 90 °C high in the mountains, and why does a syringe get harder to push? Move the temperature and watch particlesMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/periodic-table/https://edubun.com/en/chemistry/periodic-table/All 118 known elements fit on one chart of 18 columns and 7 rows. Raise the tiles in 3D by mass, size or electronegativity and the patterns that chemists uMon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/periodic-table/atomic-radius/https://edubun.com/en/chemistry/periodic-table/atomic-radius/A caesium atom has about two and a half times the radius of a fluorine atom: 343 pm against 135 pm in PubChem.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/periodic-table/how-the-table-is-organised/https://edubun.com/en/chemistry/periodic-table/how-the-table-is-organised/Element 1 is hydrogen and element 118 is oganesson, named in 2016. Every number in between is filled.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/periodic-table/mendeleev-and-the-gaps/https://edubun.com/en/chemistry/periodic-table/mendeleev-and-the-gaps/In 1869 about two thirds of the natural elements were known. Mendeleev left spaces for the rest.Mon, 26 Oct 2026 00:00:00 GMT https://edubun.com/en/chemistry/reactions/https://edubun.com/en/chemistry/reactions/Burning gas, rusting iron and baking soda fizzing in vinegar are all atoms trading partners. Balance equations with atom-count bars, weigh a reaction in a Mon, 26 Oct 2026 00:00:00 GMT