circumference

Home/Tag: circumference
20 08, 2017

What’s the equator? Geography and the Earth

By |2019-05-30T17:06:09-07:00August 20th, 2017|Physics|0 Comments

This globe shows the equator running around the widest part of the Earth. Where is the equator? The equator is an imaginary line running around the widest part of the Earth, halfway between the North Pole and the South Pole. You can't see it. Why does Earth have weather? Plate tectonics and continents What [...]

29 07, 2017

Area of a sphere – Volume of a sphere

By |2017-07-29T13:10:50-07:00July 29th, 2017|Math|0 Comments

This is a sphere. A sphere is a three-dimensional circle. Or you could say that a sphere is the set of all the points that are at the same distance from the center of the sphere. In nature, centrifugal force and gravity tend to make a lot of things into spheres: soap bubbles, for instance, atoms, and planets. The radius of a sphere [...]

29 07, 2017

What is a radius? Radius of a circle

By |2018-05-10T10:38:52-07:00July 29th, 2017|Math|0 Comments

What is a radius? The geometry of a circle What is a radius? The radius of a circle is the distance from the center point to the edge of the circle. It's the same distance anywhere on the circle, because the circle has radial symmetry. So it doesn't matter where you measure the radius on the circle, [...]

29 07, 2017

What is pi? Simple geometry – Math, circles, circumference, diameter

By |2018-04-23T16:01:03-07:00July 29th, 2017|Math|8 Comments

What is pi? The geometry of a circle What is pi? Pi is a number that is just a little bigger than 3.14. It is the number you get if you divide the circumference of any circle by its diameter. It's the same for all circles. You can approximate pi for yourself by taking some circular things like the tops [...]

29 07, 2017

What is a cylinder? Simple geometry

By |2017-07-29T09:33:37-07:00July 29th, 2017|Math|0 Comments

This is a cylinder. What can you find around your house that's a cylinder? A cylinder is a circle moved through space to make a solid form. The ends are circles that are in parallel planes, and the sides of the cylinder are the line segments that connect the circumferences of the two circles. Because the circular ends run parallel to [...]

28 07, 2017

Circumference of a circle – Geometry

By |2019-04-07T04:49:25-07:00July 28th, 2017|Math|0 Comments

The geometry of a circle, with circumference labelled What is the circumference? The circumference of a circle is the distance all the way around the circle. It's the same as the perimeter, but a special word that we only use for the perimeter of a circle. The circumference is always equal to twice the radius of the circle [...]

28 07, 2017

Proof for the area of a circle

By |2019-04-06T08:43:58-07:00July 28th, 2017|Math|0 Comments

Proof for the area of a circle: Divide a circle up into sections like an orange Euclid's proof We know it's true that A=πr-squared is the area of a circle, but how can we prove that this formula is always true for every possible circle? Here's how Euclid did it. Who was Euclid? Area of a circle More [...]

28 07, 2017

Area of a circle – Geometry

By |2017-07-28T00:00:26-07:00July 28th, 2017|Math|0 Comments

The geometry of a circle The area of a circle is the flat surface inside its circumference. The area is always equal to the radius squared, multiplied by π (pi). Here's a proof that this is always true for any circle. Learn by doing: figure out the area of some circles around you. Radius Diameter Circumference of [...]

18 07, 2017

Greek mathematics – Geometry and Proofs

By |2019-08-19T21:34:39-07:00July 18th, 2017|Greeks, Math|1 Comment

Greek mathematics: An Egyptian papyrus from about 100 AD which is a piece of one of Euclid's books Greek math: geometry not algebra Because people in ancient Greece had only very clumsy ways of writing down numbers, they didn't like algebra. Ancient Greek numbers What is algebra? All our ancient Greece articles They found it very hard [...]