0:00:02 > 0:00:04- BELL RINGS - Almost there!
0:00:04 > 0:00:06Ms Hucklebuck!
0:00:06 > 0:00:10That's it! That's my lucky tennis ball!
0:00:10 > 0:00:13- Jonathan!- Actually, it's Colin!
0:00:14 > 0:00:16THUD
0:00:17 > 0:00:19Oh, dear.
0:00:19 > 0:00:21It's not like Colin to be this late.
0:00:21 > 0:00:24Maybe the pressure finally got to him and he gave up.
0:00:24 > 0:00:27- KNOCKING - Help! I'm stuck in the pipes!
0:00:27 > 0:00:29- BOTH:- You're stuck in the pipes?
0:00:29 > 0:00:31BELL RINGS
0:00:31 > 0:00:32Positions!
0:00:32 > 0:00:33This is...
0:00:40 > 0:00:42..the floor manager.
0:00:45 > 0:00:47Stand by!
0:00:51 > 0:00:53- BOTH:- It's time for...
0:00:56 > 0:00:59Today we're asking, how does a compass work?
0:00:59 > 0:01:03The first compass was invented in China during the Han Dynasty,
0:01:03 > 0:01:05about 3,000 years ago.
0:01:05 > 0:01:08A compass is a lightweight magnet balanced on a pivot
0:01:08 > 0:01:09which we call a needle.
0:01:11 > 0:01:14No matter where you stand on Earth, a compass will point towards
0:01:14 > 0:01:15the North Pole.
0:01:15 > 0:01:17For centuries, this simple piece of equipment
0:01:17 > 0:01:20helped seafarers navigate the globe
0:01:20 > 0:01:22and led to the Age of Discovery.
0:01:22 > 0:01:26Speaking of discovery, we better go off and find Colin.
0:01:26 > 0:01:27See you shortly!
0:01:29 > 0:01:31And we're clear!
0:01:31 > 0:01:33I always wanted to say that.
0:01:33 > 0:01:37OK, Colin, I think I've got your location pinned down.
0:01:37 > 0:01:39What can you see in there?
0:01:39 > 0:01:41I can see a T-junction up ahead.
0:01:41 > 0:01:44There's plenty of dust and cobwebs and there's an awful lot
0:01:44 > 0:01:45of tennis balls.
0:01:45 > 0:01:47Rawr!
0:01:47 > 0:01:48Aah!
0:01:48 > 0:01:50Get me out of here!
0:01:50 > 0:01:51BELL RINGS
0:01:51 > 0:01:55And we're live in 5, 4, 7, 33.
0:02:00 > 0:02:03So, tell us, Dr Knowles, how on earth does a compass work?
0:02:03 > 0:02:06It's all because of the Earth's magnetic field.
0:02:06 > 0:02:09Convection currents in the liquid layers of the Earth's interior
0:02:09 > 0:02:13generate an electrical charge, a bit like a giant battery.
0:02:13 > 0:02:15Because the Earth rotates on its axis,
0:02:15 > 0:02:18this charge aligns itself with the Earth's poles,
0:02:18 > 0:02:20creating a positive charge at one end
0:02:20 > 0:02:22and a negative charge at the other.
0:02:22 > 0:02:24Just like a magnet.
0:02:26 > 0:02:29That's magnet-ificent.
0:02:29 > 0:02:30Ha-ha-ha!
0:02:30 > 0:02:34But did you know that there are actually two North Poles?
0:02:34 > 0:02:36You what now? Two North Poles?
0:02:36 > 0:02:39Because the Earth's magnetic field can vary,
0:02:39 > 0:02:43the exact location of magnetic north is always changing.
0:02:43 > 0:02:45Right now, it lies in northern Canada -
0:02:45 > 0:02:48about 1,600 kilometres from true north.
0:02:48 > 0:02:51That must be very confusing for anyone living there.
0:02:54 > 0:02:56So now you know how a compass works.
0:02:56 > 0:02:59Way-hey! See you next time!
0:03:01 > 0:03:05Please hurry up! I think I've got company!
0:03:05 > 0:03:08Hang in there, Colin! We'll get you out soon!
0:03:08 > 0:03:10OK, if he bears 23 degrees...
0:03:10 > 0:03:12'I wonder what this big red button does.
0:03:12 > 0:03:14'I probably shouldn't press it.
0:03:14 > 0:03:16'Oh, I really want to though.
0:03:16 > 0:03:18'Oh, look, I just pressed it.'
0:03:19 > 0:03:22Whoa!
0:03:22 > 0:03:23Aah!
0:03:25 > 0:03:27Aargh!
0:03:27 > 0:03:30Aargh!
0:03:30 > 0:03:31Colin, you're safe!
0:03:31 > 0:03:32Ow!
0:03:34 > 0:03:37Oh, crumpets.
0:03:37 > 0:03:39Oh, look, you found it.
0:03:39 > 0:03:42Oh, what would I do without you, McCork?
0:03:42 > 0:03:44What can I say, Mrs Hucklebadger? I do my best.
0:03:44 > 0:03:46Oh...
0:03:46 > 0:03:48Just typical!
0:04:00 > 0:04:01Brain Freeze!