# Test particle

**test chargetest particlestest masscharged test particle theoretical point particleinfinitesimal masstest body**

In physical theories, a test particle, or test charge, is an idealized model of an object whose physical properties (usually mass, charge, or size) are assumed to be negligible except for the property being studied, which is considered to be insufficient to alter the behavior of the rest of the system.wikipedia

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### Classical field theory

**field equationsclassical field theoriesfield theory**

:.In the case where one of the masses is much larger than the other (m_1\gg m_2), one can assume that the smaller mass moves as a test particle in a gravitational field generated by the larger mass, which does not accelerate.

The gravitational field of M at a point r in space is found by determining the force F that M exerts on a small test mass m located at r, and then dividing by m:

### Electric field

**electricelectrostatic fieldelectrical field**

In simulations with electric fields the most important characteristics of a test particle is its electric charge and its mass.

The electric field is defined mathematically as a vector field that associates to each point in space the (electrostatic or Coulomb) force per unit of charge exerted on an infinitesimal positive test charge at rest at that point.

### General relativity

**general theory of relativitygeneral relativity theoryrelativity**

In metric theories of gravitation, particularly general relativity, a test particle is an idealized model of a small object whose mass is so small that it does not appreciably disturb the ambient gravitational field.

According to Newton's law of gravity, and independently verified by experiments such as that of Eötvös and its successors (see Eötvös experiment), there is a universality of free fall (also known as the weak equivalence principle, or the universal equality of inertial and passive-gravitational mass): the trajectory of a test body in free fall depends only on its position and initial speed, but not on any of its material properties.

### Gravitational field

**gravity fieldgravitationalgravitational fields**

In metric theories of gravitation, particularly general relativity, a test particle is an idealized model of a small object whose mass is so small that it does not appreciably disturb the ambient gravitational field.

is the mass of the test particle,

### Coulomb's law

**Coulomb forceelectrostatic forceCoulomb interaction**

Multiplying this field by a test charge gives an electric force (Coulomb's law) exerted by the field on a test charge.

An electric field is a vector field that associates to each point in space the Coulomb force experienced by a test charge.

### Electrovacuum solution

**electrovacuum**

In the case of test particles in a vacuum solution or electrovacuum solution, this turns out to imply that in addition to the tidal acceleration experienced by small clouds of test particles (spinning or not), spinning test particles may experience additional accelerations due to spin-spin forces.

In this case, the electromagnetic field is often called a test field, in analogy with the term test particle (denoting a small object whose mass is too small to contribute appreciably to the ambient gravitational field).

### Point particle

**point chargepoint massparticle**

### Theoretical physics

**theoretical physicisttheoreticaltheoretical physicists**

In physical theories, a test particle, or test charge, is an idealized model of an object whose physical properties (usually mass, charge, or size) are assumed to be negligible except for the property being studied, which is considered to be insufficient to alter the behavior of the rest of the system.

### Mass

**inertial massgravitational massweight**

In simulations with electric fields the most important characteristics of a test particle is its electric charge and its mass. In physical theories, a test particle, or test charge, is an idealized model of an object whose physical properties (usually mass, charge, or size) are assumed to be negligible except for the property being studied, which is considered to be insufficient to alter the behavior of the rest of the system.

### Charge (physics)

**chargechargescharged**

In physical theories, a test particle, or test charge, is an idealized model of an object whose physical properties (usually mass, charge, or size) are assumed to be negligible except for the property being studied, which is considered to be insufficient to alter the behavior of the rest of the system.

### Volume

**volumetriccapacityOrders of magnitude (volume)**

In physical theories, a test particle, or test charge, is an idealized model of an object whose physical properties (usually mass, charge, or size) are assumed to be negligible except for the property being studied, which is considered to be insufficient to alter the behavior of the rest of the system.

### Computer simulation

**computer modelsimulationcomputer modeling**

In addition to its uses in the simplification of the dynamics of a system in particular limits, it is also used as a diagnostic in computer simulations of physical processes.

### Newton's law of universal gravitation

**law of universal gravitationuniversal gravitationNewtonian gravity**

The easiest case for the application of a test particle arises in Newtonian gravity.

### Center of mass

**center of gravitycentre of gravitycentre of mass**

In the general solution for this equation, both masses rotate around their center of mass R, in this specific case:

### Newton's laws of motion

**Newton's second lawNewton's third lawNewton's second law of motion**

with r as the distance between the massive object and the test particle, and \hat{r} is the unit vector in the direction going from the massive object to the test mass. Newton's second law of motion of the smaller mass reduces to

### Satellite

**satellitesartificial satelliteartificial satellites**

This approach gives very good approximations for many practical problems, e.g. the orbits of satellites, whose mass is relatively small compared to that of the Earth.

### Earth

**Earth's surfaceterrestrialworld**

This approach gives very good approximations for many practical problems, e.g. the orbits of satellites, whose mass is relatively small compared to that of the Earth.

### Electric charge

**chargeelectrical chargecharged**

In simulations with electric fields the most important characteristics of a test particle is its electric charge and its mass.

### Coulomb constant

**Coulomb's constantCoulomb force constantelectrostatic constant**

where k is Coulomb constant.

### Einstein field equations

**Einstein field equationEinstein's field equationsEinstein's field equation**

According to the Einstein field equations, the gravitational field is locally coupled not only to the distribution of non-gravitational mass-energy, but also to the distribution of momentum and stress (e.g. pressure, viscous stresses in a perfect fluid).

### Mass–energy equivalence

**mass-energy equivalencemass-energyE=mc²**

According to the Einstein field equations, the gravitational field is locally coupled not only to the distribution of non-gravitational mass-energy, but also to the distribution of momentum and stress (e.g. pressure, viscous stresses in a perfect fluid).

### Momentum

**conservation of momentumlinear momentummomenta**

According to the Einstein field equations, the gravitational field is locally coupled not only to the distribution of non-gravitational mass-energy, but also to the distribution of momentum and stress (e.g. pressure, viscous stresses in a perfect fluid).

### Stress (mechanics)

**stressstressestensile stress**

### Fluid solution

**perfect fluidfluiddust**

### Vacuum solution (general relativity)

**vacuum solutionvacuum solutionsVacuum**

In the case of test particles in a vacuum solution or electrovacuum solution, this turns out to imply that in addition to the tidal acceleration experienced by small clouds of test particles (spinning or not), spinning test particles may experience additional accelerations due to spin-spin forces.