Physics Help Forum Does Light obey Newtons First Law?

 Light and Optics Light and Optics Physics Help Forum

 Apr 27th 2018, 09:24 AM #1 Senior Member     Join Date: Feb 2017 Posts: 203 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?
 Apr 27th 2018, 11:23 AM #2 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 995 Newton's laws apply to material bodies. Light is not a material body. So Newton's Laws do not apply to light. topsquark likes this.
 Apr 28th 2018, 12:23 AM #3 Senior Member     Join Date: Feb 2017 Posts: 203 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?
Apr 28th 2018, 02:29 AM   #4
Senior Member

Join Date: Apr 2015
Location: Somerset, England
Posts: 995
 Originally Posted by avito009 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.

 Tags law, light, newtons, obey

 Thread Tools Display Modes Linear Mode

 Similar Physics Forum Discussions Thread Thread Starter Forum Replies Last Post kinhew93 Kinematics and Dynamics 14 Sep 6th 2013 10:04 PM FlexedCookie Kinematics and Dynamics 9 Mar 1st 2011 02:39 PM amiv4 Kinematics and Dynamics 0 Feb 2nd 2009 03:40 PM Morgan82 Kinematics and Dynamics 1 Oct 23rd 2008 10:59 AM Morgan82 Kinematics and Dynamics 1 Oct 20th 2008 06:24 PM