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Old Apr 27th 2018, 09:24 AM   #1
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Does Light obey Newtons First Law?

We know that Light travels slower in mediums other than vacuum. Scientists were able to drag light to the speed of sound. We know that drag is a force. So is it not drag that slows the speed of light in a fluid?

https://phys.org/news/2011-07-scientists.html

Newtons First Law states: An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an external force.

Is not drag an external force due to which light changes speed? If so does not light obey Newtons First Law?
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Old Apr 27th 2018, 11:23 AM   #2
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Newton's laws apply to material bodies.

Light is not a material body.

So Newton's Laws do not apply to light.
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Old Apr 28th 2018, 12:23 AM   #3
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Some Points.

If light is slowed down due to drag in a fluid then it must have some area as drag is dependent on area. But only solid objects have area. So does that mean photons have mass since only a solid object has area?

Lets define Area: Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat.

When we see things we see the light that is reflected from that object. Which means light as a particle is covering the shape of say a sphere in case light is reflected from a ball. But light is not material as you say.

If light is non-material then how can it have area?
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Old Apr 28th 2018, 02:29 AM   #4
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Originally Posted by avito009 View Post
If light is slowed down due to drag in a fluid then it must have some area as drag is dependent on area. But only solid objects have area. So does that mean photons have mass since only a solid object has area?

Lets define Area: Area can be understood as the amount of material with a given thickness that would be necessary to fashion a model of the shape, or the amount of paint necessary to cover the surface with a single coat.

When we see things we see the light that is reflected from that object. Which means light as a particle is covering the shape of say a sphere in case light is reflected from a ball. But light is not material as you say.

If light is non-material then how can it have area?
Well it's good that we are discussing in proper manner, unlike the other thread about the plasma globe which is about basically a similar question.
So well done on that.

Light no more has 'area' because it interacts with its transmission medium than it has mass because it has momentum.

The interaction is due to the medium changing the electromagnetic environment. We measure this as a change in capacitance and/or inductance ie impedance.
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