holes between a pair of postage stamps from a coil of stamps Holes can occur for a number of reasons, including natural processes and intentional actions by humans or animals. Holes in the ground that are made intentionally, such as holes made while searching for food, for replanting trees, or
postholes made for securing an object, are usually made through the process of
digging. Unintentional holes in an object are often a sign of
damage.
Potholes and
sinkholes can damage human settlements. Holes can occur in a wide variety of materials, and at a wide range of scales. The smallest holes observable by humans include pinholes and
perforations, but the smallest phenomenon described as a hole is an
electron hole, which is a position in an
atom or
atomic lattice where an
electron is missing. The largest phenomenon described as a hole is a
supermassive black hole, an astronomical object which can be billions of times more massive than Earth's
sun. The deepest hole on Earth is the man-made
Kola Superdeep Borehole, with a true vertical drill-depth of more than 7.5 miles (12 kilometers), which is only a fraction of the nearly 4,000 mile (6,400 kilometer) distance to the center of the Earth.
In mathematics , the doughnut and the coffee cup are considered to fall into the same mathematical "genus" because each has one hole. In
mathematics, holes are examined in a number of ways. One of these is in
homology, which is a general way of associating certain algebraic objects to other mathematical objects such as
topological spaces. Homology groups were originally defined in
algebraic topology, and homology was originally a rigorous mathematical method for defining and categorizing holes in a mathematical object called a
manifold. The initial motivation for defining homology groups was the observation that two shapes can be distinguished by examining their holes. For instance, a circle is not a disk because the circle has a hole through it while the disk is solid, and the ordinary sphere is not a circle because the sphere encloses a two-dimensional hole while the circle encloses a one-dimensional hole. Because a hole is immaterial, it is not immediately obvious how to define one or distinguish it from others. Another is the notion of
homotopy group: these are invariants of a topological space that, when non-trivial (one also says in this case that the space is not
k-connected), detect the presence of "holes" in the sense that the space contains a
sphere that cannot be contracted to a point. The term of hole is often used informally when discussing these objects. For surfaces a notion closer to the intuitive meaning exists: the
genus of a connected,
orientable surface is an
integer representing the maximum number of cuttings along non-intersecting closed simple
curves without rendering the resultant
manifold disconnected. In layman's terms, it is exactly the number of "holes" the surface has, when represented as a submanifold in 3-space.
In physics In physics,
antimatter is pervasively described as a hole, a location that, when brought together with ordinary matter to fill the hole, results in both the hole and the matter cancelling each-other out. This is analogous to patching a pothole with asphalt, or filling a bubble below the surface of water with an equal amount of water to cancel it out. The most direct example is the
electron hole; a fairly general theoretical description is provided by the
Dirac sea, which treats
positrons (or
anti-particles in general) as holes. Holes provide one of the two primary forms of conduction in a
semi-conductor, that is, the material from which
transistors are made; without holes, current could not flow, and transistors turn on and off by enabling or disabling the creation of holes.
In biology near
Ambergris Caye,
Belize, is an underwater
sinkhole. Animal bodies tend to contain specialized holes which serve various biological functions, such as the intake of oxygen or food, the excretion of waste, and the intake or expulsion of other fluids for reproductive purposes. In some simple animals, a single hole serves all of these purposes. The formation of holes is a significant event in the development of an animal:
Gramicidin A, a
polypeptide with a helical shape, has been described as a portable hole. When it forms a
dimer, it can embed itself in
cellular bilayer membranes and form a hole through which water molecules can pass.
Blind and through In
engineering,
machining, and
tooling, a hole may be a
blind hole or a
through hole (also called a
thru-hole or
clearance hole). A blind hole is a hole that is
reamed,
drilled, or
milled to a specified depth without breaking through to the other side of the workpiece. A through hole is a hole that is made to go completely through the material of an object. In other words, a through hole is a hole that goes all the way through something.
Taps used for through holes are generally tapered since it will tap faster and the chips will be released when the tap exits the hole. The etymology of the
blind hole is that it is not possible to see through it. It may also refer to any feature that is taken to a specific depth, more specifically referring to internally
threaded hole (tapped holes). Not considering the drill point, the depth of the blind hole, conventionally, may be slightly deeper than that of the threaded depth. There are three accepted methods of threading blind holes: • Conventional
tapping, especially with bottom taps •
Single-point threading, where the workpiece is rotated, and a pointed cutting tool is fed into the workpiece at the same rate as the pitch of the internal thread. Single-pointing inside a blind hole, like
boring inside one, is inherently more challenging than doing so in a through hole. This was especially true in the era when manual machining was the only method of control. Today,
CNC makes these tasks less stressful, but nevertheless still more challenging than with through holes. • Helical interpolation, where the workpiece remains stationary and
Computer Numerical Control (CNC) moves a
milling cutter in the correct helical path for a given thread, milling the thread. At least two U.S. tool manufacturers have manufactured tools for
thread milling in blind holes: Ingersoll Cutting Tools of Rockford, Illinois, and Tooling Systems of Houston, Texas, who introduced the Thread Mill in 1977, a device that milled large internal threads in the blind holes of oil well
blowout preventers. Today many CNC milling machines can run such a thread milling cycle (see a video of such a cut in the "External links" section). One use of through holes in electronics is with
through-hole technology, a mounting scheme involving the use of
leads on the components that are inserted into holes drilled in
printed circuit boards (PCB) and
soldered to pads on the opposite side either by manual assembly (hand placement) or by the use of automated insertion mount machines.
Pinholes A
pinhole is a small hole, usually made by pressing a thin, pointed object such as a
pin through an easily penetrated material such as a
fabric or a very thin layer of
metal. Similar holes made by other means are also often called pinholes. Pinholes may be intentionally made for various reasons. For example, in
optics pinholes are used as
apertures to select certain rays of light. This is used in
pinhole cameras to form an image without the use of a
lens. Pinholes on
produce packaging have been used to control the atmosphere and relative humidity within the packaging. In many fields, pinholes are a harmful side effect of manufacturing processes. For example, in the assembly of
microcircuits, pinholes in the
dielectric insulator layer coating the circuit can cause the circuit to fail. Therefore, "[t]o avoid pinholes that might protrude through the entire thickness of the dielectric layer, it is a common practice to screen several layers of dielectric with drying and firing after each screening", thereby preventing the pinholes from becoming continuous. ==Philosophy and psychology==