Photon Momentum: The Impact of Light on Movement in Space

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SUMMARY

The discussion centers on the momentum of photons and its effects on movement in space. It confirms that when a flashlight is turned on in a vacuum, the user experiences a push in the opposite direction due to Newton's third law. Additionally, the impact of photons from a star can indeed cause movement, which is the principle behind solar sails. The momentum of photons is quantified as h/lambda, and the change in momentum upon reflection is 2h/lambda, leading to forward motion.

PREREQUISITES
  • Understanding of Newton's third law of motion
  • Familiarity with the concept of photon momentum
  • Knowledge of solar sails and their application in space propulsion
  • Basic grasp of the equation for photon momentum (h/lambda)
NEXT STEPS
  • Research the principles of solar sails and their design
  • Explore the implications of photon momentum in spacecraft propulsion
  • Learn about the Pioneer anomaly and its relation to photon momentum
  • Investigate current initiatives like Breakthrough Starshot for light sail propulsion
USEFUL FOR

Astronomers, physicists, aerospace engineers, and anyone interested in the mechanics of light and its applications in space travel.

Ebi
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TL;DR
Can momentum of photons create impact forces?
We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if:
1- I turn on a flashlight (torch), would I be pushed in the opposite direction which the flashlight is facing (Newton's third law)?
2- If a star is shedding light on me (its photons hit my body), would I start moving due the impact of photos?
 
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Yes. That's the principle behind solar sails. Also what was deemed to be the cause of the Pioneer anomaly.
 
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Ebi said:
Summary:: Can momentum of photons create impact forces?

We know that photons (light) are massless but they have momentum. Now suppose I am in the space far away from planets/stars that there is no external force exerts on me, if:
1- I turn on a flashlight (torch), would I be pushed in the opposite direction which the flashlight is facing (Newton's third law)?
2- If a star is shedding light on me (its photons hit my body), would I start moving due the impact of photos?
Yes, momentum is momentum and it's conserved!
 
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Yes, the momentum of a photon is given by h/lambda. And when the photon hits you and reflects back, the change in the momentum of photon is given by 2h/lambda (assuming normal incidence), you would start moving forward with that momentum.
The momentum of photons (from sunlight) have been used in the past to propel spacecraft s and are called as solar sails. There are efforts currently by breakthrough initiatives, to use ground based laser source to propel light sails to the exoplanet Alpha Centauri. Follow this link to learn more about that.
 

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