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?

A Light Dependent Resistor(LDR) could be used in certain electronic circuits as an automatic switch along with a transistor. It works on the principle that the resistance in the circuit is inversely proportional to the light intensity, thus implying that the resistance increases as the vicinity gets darker, triggering a flow of current. I believe this has something to do with the photoelectric effect, but could someone please explain the correlation between the resistance and the light intensity as well as why an increase in the resistance triggers the flow of current and not the other way around(i.e a decrease in resistance triggering a flow of current)?

Why are four-person bobsleighs faster than two-person bobsleighs? Is it because they have two extra people pushing at the start and therefore are faster throughout their run or is it to do with weight and momentum? Surely there comes a point when the extra weight slows the bob too much? A few friends and I spent an hour or so arguing over this the other week, divided into those who thought it was the extra weight and others who thought it was the extra runners.

Alan Kane, Glasgow, UK

When I open a new jar of marmalade the contents are a nice, semi-solid, homogenous mass with a smooth surface, however old the jar is. Yet when I make a spoonful-sized hole in the flat surface to remove some marmalade, the next time I open the jar a couple of days later, the hole has started to fill with a syrupy liquid. What is it about breaking the surface of the marmalade that sets this process in motion? It continues until the jar is empty.

I seem to remember reading at university that light was affected by gravity and was proven by an experiment where the sun would "bend" light allowing stars that should be obscured by the sun to be seen. I have read that photons are massless, so, is it the EM radiation that is affected by gravity and if so surely that would prove that light had mass.

Consider this question:

A ball thrown directly upwards into the air takes 10 seconds to return to the thrower. Calculate the projection speed and it's return speed.

Now some people consider both the projection speed and the return speed to be the same. But if the words "ball thrown" and "thrower" is replaced with the words "gun shot" and "shooter", it could change everything, right?

So does the upwards force=downwards force?

Imagine that you have an infinite amount of dominos(same mass) lined up(at the same distance).

And let's say that the first domino have been pushed with great force(like that of a bullet.)

Now here's the question. What will happen to the toppling speed after a very, very long time?

1. They will still topple with the same speed like the first one.

2. The dominos will slow down until it reaches a constant speed.

3. It would stop toppling at some point.

4. Other answer(please state).

Passengers inside an aeroplane, that is going through a free fall can feel the effect and if the fall is fast enough, they could even be levitated inside the plane. The same effect goes with a free falling elevator.

But passengers inside a bullet train feels no significant changes even though the speed of a bullet train is faster than that of a free-falling elevator.

Is there any explanation for this?