Does all matter with a temperature radiate?

[Ralphonsicus]

Is there a way to find out by how much a temperature of 20 degrees Kelvin (or Celsius, same magnitude) will drop, with time?

Let's say the 20 degrees is water, and there's 100ml of it.

 

[lntz]

it depends upon what the water is contained in.

if your water is in a metal container then it will lose energy much faster than if it were in a polystyrene cup.

the energy required to heat a certain amount of water by a certain temperature is = mass*specific heat capacity*temp.change in kelvin

ignoring radiation and simply looking at conduction you could use the same equation if you knew the specific heat capacity of the water's container to work out how much energy the water would lose to its container.

these are just my thoughts, and not necessarily correct.

 

[Khashishi]

It will radiate, but the amount depends on details of the system. It's not optically thick, so black body doesn't apply.