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Galilean Transformation

Galilean Transformation Definition

Galilean transformations can be represented as a set of equations in classical physics. They are also called Newtonian transformations because they appear and are valid within Newtonian physics. The Galilean transformation equation relates the coordinates of space and time of two systems that move together relatively at a constant velocity. Galilean transformations form a Galilean group that is inhomogeneous along with spatial rotations and translations, all in space and time within the constructs of Newtonian physics. Again, without the time and space coordinates, the group is termed as a homogenous Galilean group. The law of inertia is valid in the coordinate system proposed by Galileo.

What are Galilean Transformations?

To explain Galilean transformation, we can say that the Galilean transformation equation is an equation that is applicable in classical physics. Galilean equations and Galilean transformation of wave equation usually relate the position and time in two frames of reference. These two frames of reference are seen to move uniformly concerning each other. 

Thus, the Galilean transformation definition can be stated as the method which is in transforming the coordinates of two reference frames that differ by a certain relative motion that is constant.

A group of motions that belong to Galilean relativity which act on the four dimensions of space and time and form the geometry of Galilean is called a Galilean group. 

All these concepts of Galilean transformations were formulated by Gailea in this description of uniform motion. The topic of Galilean transformations that was formulated by him in his description of uniform motion was motivated by one of his descriptions. The description that motivated him was the motion of a ball rolling down a ramp.

Galilean Equations

The Galilean equations can be written as the culmination of rotation, translation, and uniform motion all of which belong to spacetime. Galilean transformation derivation can be represented as such:

To derive Galilean equations we assume that ‘x' represents a point in the three-dimensional Galilean system of coordinates. ‘t ’represents a point in one-dimensional time in the Galilean system of coordinates.

A uniform Galilean transformation velocity in the Galilean transformation derivation can be represented as ‘v’.

Thus, (x,t) → (x+tv,t) ; where v belongs to R3 (vector space).

A translation is given such that (x,t) →(x+a, t+s) where a belongs to R3 and s belongs to R.

A rotation is given by (x,t)→(Gx,t), where we can see that G: R3 →R3 is a transformation that is orthogonal in nature.

Galilean and Lorentz Transformation

Both the homogenous as well as non-homogenous Galilean equations of transformations are replaced by Lorentz equations. Galilean and Lorentz transformation can be said to be related to each other. Galilean transformation of the wave equation is nothing but an approximation of Lorentz transformations for the speeds that are much lower than the speed of light. 

Between Galilean and Lorentz transformation, Lorentz transformation can be defined as the transformation which is required to understand the movement of waves that are electromagnetic in nature. To explain Galilean transformation, we can say that it is concerned with the movement of most objects around us and not only the tiny particles.

For the Galilean transformations, in the space domain, the only mixture of space and time is found that is represented as, 

\[{x}' = (x-vt)\]; where v is the Galilean transformation equation velocity.

In Lorentz transformation, on the other hand, both ‘x’ and ‘t’ coordinates are mixed and represented as

\[{x}' = \gamma (x-vt) and {ct}'=(ct-\beta x)\]

Although, there are some apparent differences between these two transformations, Galilean and Lorentz transformations, yet at speeds much slower than light, these two transformations become equivalent. The differences become significant for bodies moving at speeds faster than light.

Did You Know?

  1. According to the Galilean equations and Galilean transformation definition, the ideas of time, length, and mass are independent of the relative motion of the person observing all these properties.

  2. According to the theory of relativity of Galileo Galilei, it is impossible by any mechanical means to state whether we are at rest or we are moving. If we consider two trains are moving in the same direction and at the same speed, the passenger sitting inside either of the trains will not notice the other train moving.

  3. The coordinate system of Galileo is the one in which the law of inertia is valid.


It should always be remembered that the Galilean equations are applicable and physically valid in a Newtonian framework. They are definitely not applicable to the coordinate systems that are moving relative to each other at speeds that approach the speed of light. Galilean transformations formally express certain ideas of space and time and their absolute nature. 

FAQs on Galilean Transformation

1. Define Galilean Transformation? When is Galilean Transformation Valid?

In physics, Galilean transformation is extremely useful as it is used to transform between the coordinates of the reference frames. The reference frames must differ by a constant relative motion. Galilean transformation works within the constructs of Newtonian physics. Galilean transformations can be classified as a set of equations in classical physics. 

Galilean transformation is valid for Newtonian physics. These transformations are applicable only when the bodies move at a speed much lower than that of the speeds of light. The Galilean transformations relate the space and time coordinate of two systems that move at constant velocity. The velocity must be relative to each other.

2. Compare Galilean and Lorentz Transformation.

Lorentz transformation can be defined as the general transformations of coordinates between things that move with a certain mutual velocity that is relative to each other. Lorentz transformation considers an invariant speed of c which varies according to the type of universe. Lorentz transformations are used to study the movement of electromagnetic waves.

The Galilean transformation of the wave equation is concerned with all the tiny particles as well as the movement of all other bodies that are seen around us. Interestingly, the difference between Lorentz and Galilean transformations is negligible when the speed of the bodies considered is much lower than the speed of light. The difference becomes significant when the speed of the bodies is comparable to the speed of light.

3. What is the Galilean frame for references?

The Galilean frame of reference is a four-dimensional frame of reference. Although there is no absolute frame of reference in the Galilean Transformation, the four dimensions are x, y, z, and t.

4. What is the limitation of Galilean transformation? 

The Galilean transformation has some limitations. 

  • It violates both the postulates of the theory of special relativity. 

  • The first postulate is violated as the equations of electricity and magnesium become very different when the Galilean transformation is used in two inertial frames of reference. 

  • In the second one, it is violated as in an inertial frame of reference, the speed of light would be c’= c−v. 

  • That is why Lorentz transformation is used more than the Galilean transformation.