# If light pushes us question.

1. May 27, 2013

### Discor

Hello I am new to physics and I did no knew were else I can ask this question so i am sorry if I am in the wrong place.
My question is : if light makes us heavier by pushing our atoms does it means we are heavier in the day time? and the answer should be yes but then I thought if light pushes me, then it also pushes the Earth, which means that the earth is pushing me when I am in the opposite site of the sunlight (the other part of the sphere) meaning that I am always weight the same. but should not the of the sunlight travel trough the earth with the speed of sound?
My English is bad and I am very sorry for it.
But I am weary confused and i hope you can help me.
I Sincerely thank you!

2. May 27, 2013

### Staff: Mentor

If you had a very sensitive scale then it could indeed measure the radiation pressure from sunlight.

3. May 27, 2013

### jbriggs444

Light does push on us. But not on all our atoms. Just on the ones in our skin and clothes. It does not penetrate very far. It does not push very hard. Not enough to be easily detectable. You have to use fairly sensitive instruments in laboratory conditions to detect light pressure.

But pretend for the moment that light pressure was large enough to measure easily...

Because the light does not penetrate very far, that means that it would still only directly affect surfaces facing the sun. Light pressure would correlate well with surface area. It would not correlate well with volume or with mass.

Suppose that you had two bodies. One had a high surface area to mass ratio and one had a low surface area to mass ratio. Which would be accelerated more strongly by light pressure?

If you turned on the sun (like turning on a light switch) then, theoretically, this would create a pressure wave. Yes, this pressure wave would move through the Earth at the speed of sound.

4. May 27, 2013

### Discor

Thank you!
I am less confused now