I would like to make a plexiglass airtight housing to put a camera in it at the bottom of my pond.
This box has a capacity of, for example, 5 liters. How can I calculate the weight that must be in this to be able to leave it on the bottom.
So I’m going to move +/- 5 liters of water, which means I’m going to move 5 kg of water, so if I put something of 5 kg in the water with the same dimensions, it will sink immediately. But what if there is also air in the housing. Then I assume more weight is needed? But how can I calculate how much (for example) lead I would need, since it has quite a high specific gravity?
Answer
Your reasoning is correct, right up to the point that you are talking about the sky. Even the air has a weight, 5 liters of air weigh more than 5 liters of vacuum
What you need in the box is
5 kg for the water that moves the box
– the weight of the box itself
– the weight of what is in the box (ie air and camera).
You already understand that you can neglect the weight of the air, which is within the error limit of the measurements.
A boat that displaces less water than its weight will sink. Whether it is filled with lead or with air or vacuum.
Easy to try with an empty mustard pot in the sink or bath. More convenient than in the pond, certainly in this season.
Greetings
Answered by
Bart De Mey
Kapeldreef 75 3001 Leuven
http://www.imec-int.com
.