Most people who hold babies know that the moment babies go to sleep, they seem to gain weight. Of course, a baby's weight doesn't really change when they fall asleep, so why does the limp, floppy weight of a sleeping baby seem greater than it actually is?
Changing Perceptions Of Weight
A sleeping baby in your arms feels heavier because you must constantly adjust your own movements to compensate for their floppiness. Your muscles work harder to carry a child who's asleep, and your brain perceives this increase in work as an increase in the child's weight, though, of course, the weight of the baby stays the same.
To picture this, think about carrying a twenty-pound bag of water. You would continually have to rearrange how you were holding that bag to make up for how the weight shifted due to the water sloshing around.
In a similar way, you must continually adjust how you are holding or carrying a sleeping baby because they aren't able to control their own muscles to maintain a steady posture. Their inability to control their posture and movements makes them floppy, just like that bag of water.
Protesters To Take Advantage
Now, freeze your twenty-pound bag of water. Though it would be cold and slippery, it would feel lighter because it is a solid weight that doesn't require you to constantly make minute adjustments in order to carry it. This is how you perceive the weight of a conscious person.
Babies aren't the only ones who seem heavier when they go limp. Dogs and cats also seem to gain weight when they go to sleep. And political protesters take advantage of this phenomenon by completely relaxing their muscles when police try to drag them away from a protest.