Asteroids, comets and meteors
These three short online lessons discuss asteroids, comets and meteors.
These three short online lessons discuss asteroids, comets and meteors.
Introduction to passive and active transport
Osmosis is the movement of water across a semi-permeable membrane from an area of low solute concentration to an area of high solute concentration. Osmosis helps regulate the flow of water in and out of cells, which is crucial to their function.
Other objects in the solar system are discussed in this online textbook viz. asteroids, meteorites, comets and dwarf planets.
Electric charge comes in two varieties, which we call positive and negative. Like charges repel each other, and unlike charges attract each other. Thus, two positive charges repel each other, as do two negative charges. A positive charge and a negative charge attract each other.
How do we know there are two types of electric charge? When various materials are rubbed together in controlled ways, certain combinations of materials always result in a net charge of one type on one material and a net charge of the opposite type on the other material. By convention, we call one type of charge positive and the other type negative.