Dynamical friction. The panels depict sparse areas of the universe with dark colour and dense areas with light colour. The upper panels show the density around a galaxy if the galaxy's gravity bends ...

A cook’s reaction to cockroaches in the kitchen is a good approximation of a physicist’s reaction to friction: not only is it undesirable, it is hard to get rid of. OK, our analogy falls at a last ...

Friction is an intrinsic physical phenomenon to curling. Without it, objects in motion would move endlessly, without slowing down. This would cause many safety-related problems: Cars or trains could ...