My daughter dived underwater in the swimming pool and screamed as loud as she could. I was right next to her with my head out of the water, but I could only detect the tiniest sound, at the end of the scream. But when I was underwater with her, I could hear most of the scream. Why?

Linda Simpson Katonah, New York, US

My partner swims in an indoor heated chlorinated pool most days. Her swimming cap (pictured) lasted about a year before ripping, but over that time it developed these hard brown growths. They cannot be rubbed or scratched off, and seem to be part of the cap material in some way. What are they? The cap is 100% silicone, was washed with liquid soap every day, and hung to dry in a mesh bag in her car between swims.

I know that when the swimming pool is built, it is measured, and everybody is sure 50m swimming pool has 50m. But when the competisions are there, the touch pads are put on each side of the swimming pool and it is shorter! Am I right?

I was having a discussion with my mates about what would happen if you filled a swimming pool with jelly and jumped in.

Some of the group believe you would sit happily on the surface. Others, myself included, reckon you would sink, and risk drowning as the jelly collapsed around you.

We wouldn't want anybody to be harmed, so we don't recommend experimenting to find out. But do any New Scientist readers have a theoretical answer to the question?

Ross, Bristol, UK