Why light has momentum (simplest and clearest explanation)

Why light have momentum even if photons are massless

This is because momentum is a property by which an object can influence other object’s motion, and light can do that so it has momentum

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Another reason for this is even if light has zero rest mass but it does have an energy and this energy will also correspond to an equivalent mass, this mass works as momentum

There is a lot of confusion in people’s mind regarding momentum because:

It is generally taught that

P=mv

Where, P = momentum, m = mass and v = velocity of an object

This formula is not completely wrong, but it's not completely correct as well, because it's incomplete

In the complete formula for momentum:

Momentum not only depends on the mass of an object, but also on the total energy of that object

In other words, there are 2 things which are responsible for the momentum of an object:

1-     It's mass

2-     Its energy

This means that even if the mass of an object is zero, but it has some energy, it will definitely have some momentum

In the case of light all of its momentum comes from its energy

   Can you visualize light’s momentum?

The physical significance of momentum is: how an object’s motion influences other object’s motion

Light can influence an object’s motion

Sounds counterintuitive right?

This is true, but to see this on a significant scale we need to have an extremely powerful LASER

To have an idea consider this:

We would need LASER having energy equivalent to entire united state’s energy needs for one year to move only a paper pin at 10% of the speed of light

Light is able to do all this

Another example to see light’s momentum in action is laser cooling

The term LASER brings a thought that it can make objects hot, but that’s not always true, here’s how LASER can cool objects

1-     the temperature of a substance is a measure of the kinetic energy of its particles

2-     The more energy these particles have the more is the temperature

3-     What a LASER does is that it imparts its momentum to the particles of the substance

4-     This, in turn, slows down the particles, decreasing their kinetic energy, which decreases its temperature

This same cooling technique was used to from exotic matter at the international space station 

conclusion-

light can have momentum even without having mass, and this is because momentum is a combination of energy and mass, even if the mass is zero, energy will contribute to the momentum 

light's momentum can be visualized in cooling techniques using LASER