ELI5. If I exhale before going on a scale, then inhale deeply afterwards, will the reading on the scale increase, decrease, or not change?

Question

Of course the difference is quite miniscule but I became curious while standing on my scale exhaling to look leaner than I was. Unfortunately my scale isn’t precise enough to be able to test this so here I am. Any explanation would be greatly appreciated 🙂

In: Physics

Answer 1

It shouldn’t matter assuming your air ways are open. The reason is that the air inside your lungs would displace their own weight of air outside your body giving a buoyant force to perfectly cancel our the added mass. That said if you close your air ways and pressurize your lungs you will gain weight as the air will not displace as much and you won’t have as much botany force as before.