First law of thermodynamics with negative U, Q, and W

[Sixty3]

Homework Statement

I am looking into the first law of thermodynamics.
But I'm not sure with some parts.

Homework Equations

dU=Q-W What does it mean when U Q and W are negatives.
Also solids with W=0

The Attempt at a Solution

So the equation will change to -U=-Q+W
Does it lose it's internal energy?

 

[willem2]

It's

$$dU = \delta Q - \delta W$$

If dU is negative that means that the system loses internal energy. The temperature goes down, or water freezing etc.

if $\delta Q$ is negative, the system supplies heat to its surroundings.

if $\delta W$ is negative, the system does negative work on its surroundings, this is the same as positive work done on the system