Where do you have to go on the Earth to find the strongest pull of gravity? And where might one go to find the weakest? Plus, we ask which is the most efficient method of heating water: keeping a tank-full warm or just heating what you need. Like this podcast? Please help us by <a href="https://www.thenakedscientists.com/donate">supporting the Naked Scientists</a>

What's the most efficient way to heat water?

Each week we set out to solve one of the world's weirdest, wackiest, funniest and funkiest scientific puzzles. And along with the answer there's a brand new question to think about for next time...