Crash, Bang Squelch!

Chris -   Now, it is the Cambridge Science Festival happening at the moment and one of the really big highlights certainly for me in the past and certainly this year no less of the science festival is Science on Saturday.  The University of Cambridge throws opens its doors and there are some wonderful students who lay on all kinds of demonstrations for the general public including young and earned, up and coming, scientists of tomorrow, and Harriet Johnson went along to see some of the demonstrations that were laid on yesterday.

Harriet -   I'm at the Science Festival in Cambridge where there's loads of scientific experiments being demonstrated by the students of Cambridge University.  First, we're with Isabel.

Isabel -   What we have here is a solution of sodium acetate which we've dissolved in water and we allowed it to cool down.  What we're now going to do is we're going to add a seed, some of this crystal that's already pre-formed.

Harriet -   So, at the minute, the liquid is crystal clear and then what's happened?

Isabel -   Did you see that?

Child -   It's like frozen.

Harriet -   It does look frozen.  The whole cup has turned into a hard cloudyness, hasn't it?

Isabel -   Yeah.  Give that a feel.

Child -   It's hot.

Isabel -   So here, we had to heat up to dissolve the solid in the first place into liquid.  Now, when it's forming a solid, form a solution, heat energy is released.

Mother -   It's amazing, isn't it?

Ivan -   My name is Ivan and this experiment is glow sticks.  Have you used glow sticks before?

Child -   Yeah, you like break them and they glow.

Ivan -   Yes, I have one here.  Why do you have to break them?

Child -   Because there's chemical inside and they get released when they break it?

Ivan -   Yeah, so if you break this one - so that's quite bright.  How do you think we can stop it from glowing, apart from like waiting a really, really long time?

Child -   You've could freeze the chemicals.

Ivan -   That's true.  We've actually got a bowl of ice here.  so, if you put one end in, you see the difference between the two.  The one that's not in the ice is glowing more brightly than the one that was in the ice.  So, how would you think you can make this one glow as brightly as this one again?

Child -   You could warm it up with your hands.

Ivan -   Yeah, so you try that now.

Child -   It glows again.

Ivan -   It glows again!

Adam -   Hi.  I'm Adam.  If we drop a paperclip down onto the water, as long as you don't drop it from too high, instead of sinking like we'd expect, the paperclip will actually float on the surface.  Try and look at it so the light is reflecting on the surface and you can see there's a big sort of dent in the water.  that's because the paperclip is pushing down onto the surface, and the surface is pushing back and actually holding the paperclip up.  And that's all to do with  something called surface tension.  It's like an elastic band.  It stretches itself as much as it can because water really hates touching air.  It only wants to touch other bits of water.that surface is so strong and so tight that it can actually hold up the paperclip.

Mother -   Wow!  It's amazing.

Adam -   Now, does your mum have made you do the washing up?

(laughter)

Adam -   You're very lucky.  But the thing I could actually do for fun amazingly when doing washing up is I can take this detergent. Inside it's got all these molecules with a head and a tail, and the head really loves water and the tail really hates it.  When I put the detergent in the water, all the water loves and sticks to the heads and moves away from the tails, and it makes the water much happier to be near the air and be at the surface.  So, what do you think will happen when I put the detergent near the paperclip?

Child -   It will sink.

Adam -   Let's see.  The paperclip shot across, right across the surface of the water.  and then if I do a little bit more, it'll sink straightaway.

Mother -   That was good!

Adam -   So, you would bang on when you said that it would sink, but why do you think it moved?

Child -   Because when it touched, the bubble went and hit the paperclip so it moved across.

Adam -   It hasn't actually done that.  It's actually because, if I got back to this rubber band, when the water is on the surface, it's stretched in all directions like that.  If you imagine, something that's in the middle is being pulled equally in all directions, when I add the detergent, it breaks the surface tension in one spot like there.  You see that when I break the surface tension, the elastic band pinged forward.  That's because when the surface tension there is really low, the paperclip is being pulled in every direction except that one.  So, the paperclip gets dragged along really quickly.

Chris -   Harriet Johnson who was at the Cambridge Science Festival which is happening all of this week.  You can find out more on the web if you just Google Cambridge Science Festival.