The volume of an object is a measure of the amount of space occupied by that object, and is not to be confused with mass. The volume of a mountain is much larger than the volume of a rock, for instance.
By convention, the word volume implies a three-dimensional context where:
For objects at or near the Earth's surface, height or depth often refers to the dimension of the object along the local vertical. All physical objects occupy a volume, even if some are so thin that they appear to be two-dimensional, like a sheet of paper.
The unit of volume in the International System of Units is the cubic meter, which is represented by the symbol m.
In some fields or applications, one often uses different units to simplify the discussions or writings. For instance:
Traditional units are still in encountered in some countries: Imperial units such as the gallon or the fluid ounce were in widespread use within the British Empire. Some of them are still popular in the United States, which also uses units like the bushel, the quart, the cup and the teaspoon (in cooking recipes, for example). See U.S. customary units for more examples.
The volume of an object is not a fundamental property of that object: it can change with environmental conditions such as pressure and temperature, especially if the object is highly compressible.
The volume of a mixture of fluids (liquids, gases) may or may not be equal to the sum of their volumes before they were mixed.
In mathematics, the volume of simple geometric objects, written formula_1, can often be calculated on the basis of their shape and dimensions:
The volume of a gas is typically that of its container, but it could be ill-defined, as in the case of the atmosphere, which has no clear upper limit. The volume of a liquid is often measured by pouring it into a graduated container. The volume of a small solid can be estimated by immersing it into a graduated container partially filled with a known amount of liquid, provided the solid is not soluble in the liquid.
Venus
Venus is the second planet from the sun. It has a day longer than a year. The year length of Venus is 225 Earth days. The day length of Venus is 243 Earth days. It is a "terrestrial planet" because it has a solid, rocky surface like other planets in the inner solar system. Astronomers have known Venus for thousands of years. The ancient Romans named it after their goddess Venus. Venus is the brightest thing in the night sky except for the Moon. It is sometimes called the "morning star" or the "evening star" as at some elongations it is easily seen just before the sun comes up in the morning and, at other times, just after the sun goes down in the evening. Venus comes closer to the Earth than any other planet does. A Venusian day takes about 243 Earth days.
Venus is sometimes called the sister planet of Earth as they are quite similar in size and gravity. In other ways the planets are very different. Venus' atmosphere (air) is mostly carbon dioxide with clouds of sulphuric acid. Sulphuric acid is a chemical that is very poisonous to humans.
The thick atmosphere has made it hard to see the surface, and until the twenty-first century many people thought things might live there. The pressure on Venus' surface is 92 times that of Earth. Venus has no moons. Venus spins very slowly on its axis and it spins in the opposite direction to the other planets.
It is also sometimes known as the Earth's "evil twin".
Venus is a terrestrial planet so, like the Earth, its surface is made of rock. Venus is much hotter than Earth. All the carbon dioxide in the atmosphere acts like a blanket, trapping heat from the Sun. This effect is called the greenhouse effect and it is very strong on Venus. This makes the surface of Venus the hottest of any planet's surface in the Solar System with an estimated average temperature of . This is hot enough to melt lead or zinc.
Venus has no oceans because it is much too hot for water. Venus' surface is a dry desert. Because of the clouds, only radar can map the surface. It is about 80% smooth, rocky plains, made mostly of basalt. Two higher areas called continents make up the north and south of the planet. The north is called "Ishtar Terra" and the south is called "Aphrodite Terra". They are named after the Babylonian and Greek goddesses of love.
The surface of Venus looks like it has been shaped by volcanic activity. Venus has a lots of volcanoes. The surface of Venus is estimated to be 300–600 million years old.
Venus' atmosphere is mostly carbon dioxide and nitrogen gas with clouds of sulphuric acid. Because the atmosphere is so thick or dense the pressure is very high. The pressure is 92 times the pressure on Earth, enough to crush many things.
It is impossible to see the planet's surface from space as the thick cloud layer reflects 60% of the light that hits it. The only way scientists are able to see it is by using infrared and ultraviolet cameras and radar.
Scientists believe that billions of years ago, the atmosphere of Venus could have been like Earth's atmosphere. There may have been lots of water on the surface of Venus. But after 600 million to several billion years, a greenhouse effect was caused by the evaporation of the water, which made lots of greenhouse gases in its atmosphere.
In 1967, Venera 4 found that the magnetic field of Venus was much weaker than that of Earth. This magnetic field is induced by an interaction between the ionosphere and the solar wind. Venus' magnetosphere is not strong enough to protect the atmosphere from cosmic rays.
Venus can sometimes be seen passing between the Sun and Earth. Venus looks like a black dot when seen through a special telescope. These passages are called "transits". These "transits" happen in pairs eight years apart. Then it is more than a hundred years to the next pair.
Venus orbits the Sun at an average distance of about 108 million km (67 million mi). It completes an orbit every 224.7 days. The rotation of Venus is slow. A Venusian day is longer than a Venusian year.
Many man-made satellites have been sent to Venus to study it. They are:
Mariner 2 was launched on August 27, 1962. It was made to study the atmosphere of Venus, its magnetic field, and mass. The last radio signal from Mariner 2 was received on January 3, 1963. Mariner 2 is still orbiting around the Sun today.
Venera 4 was a probe made by the Soviet Union to explore Venus. The probe had a two probes. One was designed to enter the atmosphere of Venus and use a parachute to land on the surface. Another received the information from the probe on Venus to mission controllers on Earth. Venera 4 was launched on June 12, 1967. The last radio signal from Venera 4 was received on October 18, 1967.
Mariner 5 was a spacecraft of the Mariner program. Mariner 5 was launched on June 14, 1967. The last radio signal from Mariner 5 was on October 14, 1968. Mariner 5 was made to study the magnetic field of Venus and to measure the hard ultraviolet spectrum, of the Venusian atmosphere.
Venera 9 was a spacecraft made by the Soviet Union. It consisted of a probe to orbit Venus which was called an orbiter and another probe that will land on Venus which was called a lander. It was launched on June 8, 1975. The last radio signal from the orbiter was on March 22, 1976. The last radio signal was on October 22, 1975. The orbiter was the first spacecraft to orbit Venus, while the lander was the first to return pictures from the surface of another planet.
Venera 10 was a spacecraft made by the Soviet Union. It consisted of an orbiter and a lander. It was launched on June 14, 1975.
Venera 13 was a probe in the Soviet Venera program. It was made to explore Venus. It was launched on October 30, 1981. The last radio signal from the lander was on March 1, 1982. The last radio signal from the spacecraft that took the lander to Venus was on April 25, 1983.