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Black holes – Space science – Physics

By |2018-05-31T11:49:29+00:00August 17th, 2017|Physics|

Ripples A black hole is a place in space where there is a huge amount of mass in a very small area. Because gravity is the same as mass times 1/volume, when you have a lot of mass in a small volume it makes a lot of gravity. Apparently, it makes so much gravity that even light can't get away from the black hole! [...]

Area of a sphere – Volume of a sphere

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

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 [...]

What is a pyramid? Square pyramids

By |2017-07-29T11:57:36+00:00July 29th, 2017|Math|

A pyramid with a square base. A pyramid is a three-dimensional solid form made out of triangles. Some pyramids also use a square. There are two common kinds of pyramids: triangular pyramids that you make by fitting four triangles together, and square pyramids that you make by fitting four triangles together on a square base, like the [...]

What is a prism? Rectangular and triangular prisms

By |2017-07-29T11:53:44+00:00July 29th, 2017|Math|

This is a triangular prism A prism is the solid shape you get if you move a flat polygon through space. A prism has five planes: a top, a bottom, and three sides. The most common kind of prism is a rectangular prism, made by moving a quadrilateral through space: a cube is a common example of a [...]

What is a cylinder? Simple geometry

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

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 [...]

Math and Numbers in Ancient China

By |2018-04-25T12:09:29+00:00June 7th, 2017|China, Science|

Chinese numbers: number rods Chinese numbers People in China were using written numbers by about 1500 BC, in the Shang Dynasty. This is about two thousand years later than people began to write numbers in West Asia. It's more than a thousand years later than people began to write numbers in India. Nobody knows whether [...]