How Can Light Have No Mass Yet Transfer Energy?

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    Light Mass
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Discussion Overview

The discussion centers around the concept of light having no mass while still being able to transfer energy, particularly in the context of feeling heat from light. Participants explore the implications of mass and energy transfer in relation to light and its properties.

Discussion Character

  • Conceptual clarification
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question how light can transfer energy without having mass, particularly in relation to feeling heat on the skin.
  • One participant argues that the logic connecting heat sensation to mass does not follow, suggesting a need for a deeper understanding of the equations involved.
  • Another participant clarifies that the equation E = mc² applies only to massive particles at rest and that light, which is always in motion, requires a different equation: E² = (m₀c²)² + (pc)², where p represents momentum and m₀ is rest mass.
  • It is noted that while light has no rest mass, it does carry momentum, which allows it to transfer energy.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between mass and energy transfer in light, with no consensus reached on the implications of these concepts.

Contextual Notes

Participants reference different forms of the energy-mass relationship, highlighting the limitations of applying E = mc² to light and the need for understanding momentum in the context of energy transfer.

Who May Find This Useful

This discussion may be of interest to individuals exploring the nature of light, energy transfer, and the implications of mass in physics.

danielpherlio
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Ive been looking at the E = mc2 explained on youtube and apparently light has no mass how can it have no mass but you you can feel heat on your skin from light
 
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danielpherlio said:
Ive been looking at the E = mc2 explained on youtube and apparently light has no mass how can it have no mass but you you can feel heat on your skin from light

Why should feeling heat imply mass? That logic doesn't follow.

The equation you posted is for a massive particle at rest. Look up the full version of the equation for a clue on how to apply it to light.
 
danielpherlio said:
Ive been looking at the E = mc2 explained on youtube and apparently light has no mass how can it have no mass but you you can feel heat on your skin from light

E = mc2 applies only to things that have mass when they are at rest - and light is always moving with speed c, never at rest, so the equation doesn't apply. Instead, we have to use the more general equation:
[tex]E^2 = (m_{0}c^2)^2 + (pc)^2[/tex]

Here p is the momentum and [itex]m_0[/itex] is the "rest mass" of the object; when people say that light has no mass they mean that its rest mass is zero. Light does however carry momentum (p is non-zero) so there's still some energy to warm your skin.
 
Thanks nugatory
 

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