Winter is here, and that means sooner or late it's going to snow. And that means sooner or later having to shovel some of it. Not only does this seem a largely futile activity since you can walk over snow while it's there, and if you leave it, it's all going to melt before too long. Also, it tends to result in back pain, either chronic, acute or both.
I've always assumed this is because snow appears to be light and fluffy, but is in fact much heavier, so the body is unprepared for the amount of work and the strain each lifting will take.
I think there may be more to it than that. Snow also has air in it. This does not make it any heavier, but does make it more massive. The extra air is not going to make a difference to the weight, since the snow is already floating in air, but it is going to affect the mass since you have to move all that air as well as the snow.
Japanese science-hero Denjiro-sensei performed a really good experiment to show the difference between weight and mass. He took a large balloon, something over a metre in diameter. First, he threw it uninflated across the stage at a foldable chair, which had little impact. Next he threw an inflated balloon at the same chair, causing it to fly across the stage. You could probably repeat this experiment in your own living room using a regular balloon and something like a pet bottle.
So back to shovelling snow, not only does snow look much lighter and fluffier than it actually weighs, so we are not fully prepared for the strain of the lift. It is also more massive than it is heavy, so we need more strength to move it around, changing its inertia, than we would guess just from holding up a shovelful.
