the light wave that you see traveling straight towards you. Because of polarizations, ie the two types or directions that the light vibrates in, it move sup and down and then left and right.

The electromagnetic field theory contains the answer to your question. Baisically it is due to motion of charge.

Thank you for the answer.

Yes, Prof Sharma is correct, the complete solution is in Electromagnetic Fields and wave theory.

Any particle (with mass or without mass at rest) moves of linear motion if subject to a null resulting of forces (principle of inertia). In the case of a particle with mass m_0 it is possible to define a reference where the particle is at rest.

For a massless particle (a photon) the particle moves at speed c (the speed of light) in any reference system (first postulate of special relativity). Electromagnetic fields change the state of motion (speed and curvature) of a charged particle, gravity changes the state of motion of a particle independently of its mass at rest ( photons do curve their trajectory because of a gravitational field). If you stop a free photon it will not exist anymore. Photons and movement at the speed of light c are intrinsic to their nature. Indeed, analyzed in terms of electric and magnetic field, Maxwell's equations provide the solution. A variation of the electric field generates a varying magnetic field which generates a variable electric field. This allows the generation of waves which propagates at speed c.

Dont like the question formultation, or the answers, except Vicenzos .

A particle with mass CAN move in a gravitational field, but not BECAUSE of the gravitational field. However the gravitational field helps determine the path. Same with electrical field.

A Photon does not have mass or charge.

All waves you know of, move, except standing waves.

Waves on a string move, water waves move, sound waves move, so why shoudent em waves move?

charges can produce an em field, but once created does not need anything.

The correct way to say it is: a particle accelerates because a force acts on it

(not: a particle moves because a force acts on it)

This is Newton’s law: F=m.a

‘a’ is the acceleration

‘m’ is the mass of the particle

‘F’ is the force and it can be the force of gravity, an electrical force, or anything else, such as you pushing your car if it doesn’t want to start. Even if the force is electrical, it is still the mass m that determines how big the acceleration is. If there are more forces working on the same particle then you need to add them up as vectors to find the resultant force. If there is no acceleration that means that all the forces compensate each other and there is no resultant force. The particle may still be moving. No force means that there is no change in the speed at which the particle moves and in the direction in which it moves.

A photon always moves at the speed of light, and Newton’s laws do not apply (they are a good approximation only at low speeds and they go badly wrong for elementary particles such as photons). The laws of relativity and quantum mechanics are needed to describe photon behaviour.

This has some fascinating consequences. I’ll mention some just for fun.

According to the laws of relativity, space contracts in the direction in which you move. At ordinary speeds (including the fastest speed we humans can achieve) this effect is negligible, but closer to the speed of light it is big. It is a real effect that has been verified extensively, and we cannot dismiss it as ‘too crazy to be true’. If you move at the speed of light (as a photon does) then space contracts all the way down to zero, i.e. there is no more space in the direction of travel. The 3D space effectively collapses to a 2D plane. It means that a photon originating from the big bang that reaches your eye has traversed zero space (according to itself) and that means it has also taken zero time (also according to itself) to get here (it reaches your eye instantaneously). Fascinating isn’t it? According to us here on earth it has taken some 14 billion years for that photon to reach your eye. You could say that time and space do not exist for a photon. At the same time (😊) photons are essential for time and space to exist. Another way to look at the speed of light is not as a velocity but as a conversion factor between space and time. We no longer measure the speed of light but have assigned a fixed value to it (299,792,458 m/s) hence this number does not have an error (as measurements always have) but is exact. It is a constant of nature that tells you how many seconds correspond to how many meters.

It gets even trickier because photons, and other elementary particles, can behave either like waves or like particles, depending on how you look at them. Maxwell worked out his famous wave equations of electromagnetism and the big surprise was they showed that electromagnetic waves travel at the speed of light. In fact within a certain frequency band they are light. Photons (particles) = electromagnetic waves (waves) = light.

At this point you will either be hooked and want to find out more, or you will have given up completely and just get on with life.

Denis

I think Olu is talking about the polarization of light, not that the light beam can change direction.(unless by refraction)

The electric field may be

oscilating in a plane in a direction perpendicular to the motion of the light beam.

The motion of light is governed by the wave equation, derived from the Maxwell equations.

1) "a particle with mass moves because of gravitational field" is poorly phrased; it would be better to say "a particle with mass accelerates because of gravitational field", or "a particle with mass is accelerated by a gravitational field". The velocity (movement) of the particle is secondary to its acceleration in this context.

Likewise:

2) "a particle with charge moves because of electric field" is similarly poorly phrased, better would be "a charged particle is accelerated by an electric field"

Of course, in both cases the particle may be fixed by some means, and although it experiences a force, not accelerate or move at all; thus "is accelerated by" would be even better expressed as "experiences a force due to".

Next, and deliberately out of original order, the last two; which are really rather different questions to the first two...

4) "electromagnetic wave move/propagates because of ..."; not "because of" but because that is its nature; as Maxwell's equations specify. If, in analogy to what (1) and (2) /should/ have said, you want to ask ""an electromagnetic wave accelerates..." then that would only have meaning for a localised pulse propagating in a medium of some kind, such as a curved waveguide; the answer could then be "... because of changing material properties".

3) The phrase "a photon moves because of ..." is essentially the same as (4), since under QED a photon is a single excitation of an electromagnetic field mode, which was covered by (4).

1. Gravitational fields have no effect on photon motion. It SEEMS to however, because our observations are made from an accelerated reference system. Our concept of space is also based on an accelerated reference system (not "real" space itself).

2. Readers pondering this question would benefit from an understanding of non-directional motion AND non-local motion. See:

"Beyond Einstein: non-local physics, 2nd ed."

https://www.researchgate.net/publication/334075961_Beyond_Einstein_non-local_physics_2nd_ed

and

"Intuitive Concepts for Atomic and Photon Spin Systems" https://www.researchgate.net/publication/338293585_Intuitive_Concepts_for_Atomic_and_Photon_Spin_Systems

You are trying to explain non-classical entities with the methods of classical mechanics of particles. Think of photons as excitations of the electromagnetic (em) field, as in QED. In this way, your question (a) and (b) are actually only one. Now for the motion. The em field (regarded either as a wave or as a photon), as a physical entity, carries its own energy-momentum, and when you interact with it, you will perceive a modification in your momenta measurements. Thus, for example, if you shine a monochromatic light on an electron, you will decrease the energy of the photon (Compton effect) while increasing the energy of the electron, as if it were a collision between classical particles.

To summarize, when dealing with quantum relativistic particles/fields, questions formulated in terms of "forces" are ill-posed, as others have remarked.