Glaciers flow across landscapes carrying boulders and debris e.t.c. Until recently I always assumed they travelled downhill, but I hear they can carry boulders uphill. How is this gravity defying feat possible?

Ian Jones, Solihull, UK

My colleagues and I were discussing what physical changes the flow of water goes through between leaving the tap and hitting the sink. This was noticed by feeling greater pressure when an object is held at the bottom of the stream versus closer to the tap.

Given that the volume of water flowing from the tap is a constant and that the water is subject to acceleration under gravity during it's fall, presumably the water stream is decreasing in diameter to maintain the same flow rate?

Presumably interference with the air would a place an upper limit on the speed at which the stream would remain together but what would this be and what would the upper limit be in a vacuum?

Fluorescent liquids are commonly used to inspect metallic components. The liquid is painted in a thin film on the surface. It fills any cracks, which can be as small as 2mm long x 1mm deep x 10microns wide. The excess liquid is removed and then the liquid remaining in the crack spontaneously bleeds back onto the surface from the crack.