The smallest parts of soil are sand and silt and clay. Those small parts join to make larger parts we call "clumps" or "aggregates". The clumps are made when sand and silt and clay stick together. The humus and clay and minerals in the soil are like glue. The glue sticks the sand and silt and clay together and makes clumps. The clumps make shapes by themselves. Some soils have small round clumps. Other soils have large, hard and flat clumps. The soil with small round clumps is best because it lets in air and water. A little glue is best. If the soil has only a little glue there will be space for water and air and the soil will be soft. If the soil has too much glue the soil will be hard. If the soil has no glue, there will be no space in the soil for air and water. A soil with no spaces is not healthy. Worms in the soil make a slippery glue. When worms make holes in the soil they leave some glue in the soil. Plant roots also make spaces in the soil. When the roots die they leave holes in the soil.
A soil has a "soil texture" (sand and silt and clay) and it has organic matter mixed in it. But weather changes the soil. It is cold on the Earth near the north and south poles. It is hot near the equator of the Earth. Some places on Earth get a lot of rain and some places get no rain. Hot and wet weather make one kind of soil. Cold and dry weather make another kind of soil. Rain water makes small things in the soil move down with the water. When the things in the water get stuck in the soil those things make a layer in the soil. If you dig down into the soil you may find many layers in the soil. The layers may have different colors. The layers may have different "soil textures". The top part of the soil may have a lot of humus and sand. Below that layer there may be a layer of silt. Below that layer there may be a layer of clay.
The sand stays on the top because it is large. The silt goes down a little with the water and makes a layer because it is small. The silt is smaller than some of the spaces in the soil. The clay can go down even lower with the water because it is the smallest. The sand will make one layer, the silt will make another layer and the clay will make another layer. The humus can move down with the water and make a layer too. The silt and clay and humus can move down because of the spaces in the soil. But, the silt, clay, and humus will fill the spaces in the soil. When the spaces in the soil are closed, it makes it hard for air to go into the soil. Plant roots do not go where there is no air. When we dig down we find layers in the soil.
We call those layers "soil horizons". The top horizon may be an inch (25mm) thick. We call that layer the "O" horizon or sometimes "topsoil". The next layer (horizon) is the "B" horizon. The next lower layer of soil is the "C" horizon. The bottom layer has many rocks and may be called the bedrock or "R" horizon for "rock". Deep down, there is always bedrock. But you may have to dig down a mile (a km) or more. When the soil dries, the soil may shrink and cracks will form in the soil. The soil in the top layer may fall down into the cracks. This causes the layers of soil to be changed because they are mixed. There may be many types soil where you live or only one type of soil. Different rocks make different soil textures. Different weather makes the different soil textures different. And so, there are different soils all over the world.
Organic
The word organic is used for different things:
3D
3D (or 3-D) means three-dimensional, or having three dimensions. For example, a box is three-dimensional; it is solid, and not thin like a piece of paper. It has volume, a top and bottom, left and right (sides), as well as a front and back. You can turn the box around to view it from another side (called a face, surface or simply side).
A dimension is measurable in inches, microns, miles, kilometers, or any other unit of length.
The three dimensions are often called length (or depth), width (or breadth), and height. Some purposes use other words.
3D graphics are used to make video games or animated movies. Many calculations are needed to make pictures seem three-dimensional on a screen. Modern computers usually have a GPU (Graphics Processing Unit) to handle these calculations.
Binocular vision helps people to see the third dimension easily.
In the Cartesian coordinate system, length, width, and height are given in letters (variables) to make them easier to write, or if a value is not known. Often X is width, Y is height, and Z is length. Other 3D coordinate systems such as spherical coordinates include both linear and angular measurements.
The mathematical study of 3D shapes and dimensions is called solid geometry.
Some people see time as a fourth dimension. It is also measured. It is measured in units of time such as seconds, hours, years, or any other measurement of time.
Humidity
Humidity means water vapor in the air, but not to liquid droplets in fog, clouds, or rain. Deserts usually have low humidity, and tropical regions have high humidity. The word "humid" often means that the humidity is high, which gives the feeling of being very damp (wet air), stuffy, or even sweltering when the temperature is also high. When the humidity is low, the air can be said to be "not humid" or "dry."
Higher humidity reduces the effectiveness of sweating in cooling the body by reducing the rate of evaporation of moisture from the skin.
The term "relative humidity" is used to note the amount of humidity as a percent, from 0-100%. Meteorologists use hygrometers to measure the humidity in the air.
Humidity affects the rate of evaporation. With a higher humidity, the rate of evaporation is less.
Calabi-Yau manifold
A Calabi–Yau manifold, or 'Calabi–Yau space', is a special type of manifold. It is described in certain branches of mathematics such as algebraic geometry.
The Calabi–Yau manifold's properties, such as Ricci flatness, have applications in theoretical physics. Particularly in superstring theory, the extra dimensions of spacetime might take the form of a 6-dimensional Calabi–Yau manifold. This led to the idea of string theory mirror symmetry.
Quantum mechanics
Quantum mechanics explains how the universe works at a scale smaller than atoms. It is also called quantum physics or quantum theory. Mechanics is the part of physics that explains how things move and "quantum" is the Latin word for 'how much'. A quantum of energy is the least amount possible (or the least extra amount), and quantum mechanics describes how that energy moves or interacts.
Atoms used to be considered the smallest building blocks of matter, but modern science has shown that there are even smaller particles, like protons, neutrons and electrons. Quantum mechanics describes how the particles that make up atoms work.
Quantum mechanics also tells us how electromagnetic waves (like light) work. Wave–particle duality means that particles behave like waves and waves behave like particles. (They are not two kinds of thing, they are something like both: this is their "duality".) Much of modern physics and chemistry can be described and understood using the mathematical rules of quantum mechanics.
The mathematics used to study subatomic particles and electromagnetic waves is very complex because they act in very strange ways.
Photons are particles that are point-sized, smaller than atoms. Photons are like "packets" or packages of energy. Light sources such as candles or lasers produce light in bits called photons.
The more photons a lamp produces, the brighter the light. Light is a form of energy that behaves like the waves in water or radio waves. The distance between the top of one wave and the top of the next wave is called a 'wavelength'. Each photon carries a certain amount, or 'quantum', of energy depending on its wavelength.