Meanings of the mass–energy equivalence formula
The mass–energy equivalence formula was displayed on Taipei 101 Taipei 101 is a landmark skyscraper located in Xinyi District, Taipei, Taiwan. The building, designed by C.Y. Lee & Partners and constructed primarily by KTRT Joint Venture and Samsung Engineering & Construction is the world's tallest completed skyscraper according to the Council on Tall Buildings and Urban Habitat, the arbiter of tall during the event of the World Year of Physics 2005 The year 2005 has been named the World Year of Physics in recognition of the 100th anniversary of Albert Einstein's "Miracle Year," in which he published four landmark papers, and the subsequent advances in the field of physics.Mass–energy equivalence states that any object has a certain energy, even when it isn't moving. In Newtonian mechanics In the fields of physics, classical mechanics is one of the two major sub-fields of study in the science of mechanics, which is concerned with the set of physical laws governing and mathematically describing the motions of bodies and aggregates of bodies geometrically distributed within a certain boundary under the action of a system of forces, a motionless body has no kinetic energy The kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. Negative work of the same magnitude, and it may or may not have other amounts of internal stored energy, like chemical energy Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines of the laws of thermodynamics. Chemical thermodynamics involves not only laboratory measurements of various thermodynamic properties, but also the application of mathematical methods to the study or thermal energy Thermal energy is a form of energy that manifests itself as an increase of temperature. It is also the sum of sensible heat and latent heat, in addition to any potential energy Potential energy can be thought of as energy stored within a physical system. It is called potential energy because it has the potential to be converted into other forms of energy, such as kinetic energy, and to do work in the process. The standard unit of measure for potential energy is the joule, the same as for work or energy in general it may have from its position in a field of force In physics, a field is a physical quantity associated to each point of spacetime. A field can be classified as a scalar field, a vector field, or a tensor field, according to whether the value of the field at each point is a scalar, a vector, or, more generally, a tensor, respectively. For example, the Newtonian gravitational field is a vector. In Newtonian mechanics, all of these energies are much smaller than the mass of the object times the speed of light squared, and none of these energies have anything to do with mass.
In relativity, all of the energy that moves along with an object adds up to the total mass of the body, which measures how much it resists deflection. Each potential and kinetic energy makes a proportional contribution to the mass. Even a single photon In physics, a photon is an elementary particle, the quantum of the electromagnetic field and the basic "unit" of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the traveling in empty space has a relativistic mass, which is its energy divided by c2. If a box of ideal mirrors contains light, the mass of the box is increased by the energy of the light, since the total energy of the box is its mass.
In relativity, removing energy is removing mass, and the formula m = E/c2 tells you how much mass is lost when energy is removed. In a chemical or nuclear reaction, the mass of the atoms that come out is less than the mass of the atoms that go in, and the difference in mass shows up as heat and light with the same relativistic mass. In this case, the E in the formula is the energy released and removed, and the mass m is how much the mass goes down. In the same way, when any kind of energy is added, the increase in the mass is equal to the added energy divided by c2. For example, When water is heated in a microwave oven A microwave oven, or a microwave, is a kitchen appliance that cooks or heats food by dielectric heating. This is accomplished by using microwave radiation to heat water and other polarized molecules within the food. This excitation is fairly uniform, leading to food being adequately heated throughout , a feature not seen in any other heating, the oven adds about 1.11×10−17 kg of mass for every joule of heat added to the water.
An object moves with different speed in different frames, depending on the motion of the observer, so the kinetic energy in both Newtonian mechanics and relativity is frame dependent. This means that the amount of energy, and therefore the amount of relativistic mass, that an object is measured to have depends on the observer. The rest mass is defined as the mass that an object has when it isn't moving. This is the smallest possible value of the mass of the object.
The rest mass is almost never additive: the rest mass of an object is not the sum of the rest masses of its parts. The rest mass of an object is the total energy of all the parts, including kinetic energy, as measured by an observer that sees the center of the mass of the object to be standing still. The rest mass adds up only if the parts are standing still and don't attract or repel, so that they don't have any extra kinetic or potential energy. The other possibility is that they have a positive kinetic energy and a negative potential energy that exactly cancels.
The difference between the rest mass of a bound system and of the unbound parts is exactly proportional to the binding energy Binding energy is the mechanical energy required to disassemble a whole into separate parts. A bound system has typically a lower potential energy than its constituent parts; this is what keeps the system together. The usual convention is that this corresponds to a positive binding energy of the system. A water molecule weighs a little less than two free hydrogen atoms and an oxygen atom; the minuscule mass difference is the energy that is needed to split the molecule into three individual atoms (divided by c2). Likewise, a stick of dynamite weighs a little bit more than the fragments after the explosion; the mass difference is the energy that is released when the dynamite explodes. The change in mass only happens when the system is open, and the energy escapes. If a stick of dynamite is blown up in a hermetically sealed chamber, the mass of the chamber and fragments, the heat, sound, and light is equal to the original mass of the chamber and dynamite.
<<Table of Contents In physics, mass–energy equivalence is the concept that the mass of a body is a measure of its energy content. What we ordinarily call the mass of a body is always equal to the total energy inside, up to a factor that changes the units. Or: | Next>> | Show All>>
