Helium.
holes
Helium is a gas that is weightless, odourless, and would make a barrel lighter.
a hole
The answer is a hole.
A flashlight
A hole. When you put a hole in the barrel, it reduces the weight of the barrel. But, when you remove the hole, the barrel becomes heavier.
A hole
A hole
You can put a hole in the barrel to make it weigh 8 kilograms.
you make a line graph and then put a scale on it
A hole. A hole cannot be seen, weighs nothing, and when added to a barrel, it reduces the weight of the barrel without adding any weight itself.
you make a line graph and then put a scale on it