My dd (Year 7) needs a funky science experiment she can perform.....

[maidamess]

She has at her disposal a table top, limited access to a socket, and cannot use live animals!(So growing an ear on a mouses back is out of the question)

Any ideas for something suitable that will make folk gasp but is easy to demonstrate?

raisin in a bottle of fizzy water is a good one too.

Well that would be lovely but as she has to do the experiemnt indoors, I think its out of the question. What a lovely scientist you are though

You can make a rocket with a camera film canister (if you can find one in this day and age!). Put a little vinegar in the canister, a teaspoon of bicarb on the lid. Place canister on floor and place lid firmly on.

STAND WELL BACK.

Shoots up about 10 metres. Fab.

I understand how it actually works, but what is sucking? What does the word sucking mean? When you suck using a straw, you pump air out of the straw to make a vacuum, and this means there's less pressure and the atmospheric pressure pushes the juice up the straw. We do have a word "suck" and it does have a meaning. If I say the egg is sucked into the bottle, that's an accurate use of the world suck. It doesn't have any other meaning.

If nothing (ie a vacuum) can't do anything, can it silence a ringing bell? Can it carry EM waves? IMO a vacuum can suck, because that's the meaning of suck - to remove pressure.

oohh. raisin in a bottle of fizzy water makes no mess!

get a bottle of fizzy water (cheapo one). Take off the paper wrapper, and try to get a clear plastic bottle, tescos value type job.

Pop the raisin in, and close the lid.

The raisin will sink to the bottom, because it is more dense than the water.

Bobbles of CO2 will form on the wrinkles surface of the raisin (posh name for this nucleation sites), and the CO2 comes out of solution and forms little bubbles that cling to the raisin. THis makes the raisin less dense and it will rise to the surface. the CO2 goes into the air at the top and the raisin sinks.

This will happen over and over again.

No mess. Strangely mesmerising

I would like to know something else about the eggsperiment MB if you could oblige - is it just the air cooling and contracting after the flame goes out that lowers the pressure, or is it the flame "using up" a part of the air in the bottle by combusting? was always told the latter but am not sure.

the vacuum doesn't silence the ringing bell. The bell will still vibrate, but because there are no gas particles present, the sound waves cannot be conducted to our ears. EM waves are different and can pass throug a vacuum

the problem with 'sucking' is that it was a meaning in 'normal english' which doesn't carry over into science, and this can cause long erm confusion. What matters is that there is a pressure differential with the egg. It isn't 'sucked in' it is pressed in.

I know it sounds overly pedantic, but you have to be clear if the kids are going to grasp why this is a good demo of the particulate nature of gases.

and don't get me started on the difference between respiration and breathing

tbh I'm hazy on the fine detail.

When you burn the paper (paper works best IME) you produce CO2 and water. The water forms as a liquid which you can see on the inside of the bottle. the particles in a liquid are a (lot) closer together, so while you have liberated some carbon, in the form of gaseous CO2, you have produced liquid H2O, so there are significatly less gas moleules inside than there were at the start of the experiment.

more gas particles outside, egg pushed in

I guess there may be a cooling/contracting factor as well...

the best example of the effect of cooling gases is the coke can crushing experiment.

Put a small amount of water in a coke can, and get it to boiling point. With tongs, swiftly turn it upside down and plunge into iced water. the steam inside (which forces out the air as it evaporates) quickly condenses back to a liquid, and the greater pressure outside crushes the can in a second.

was going to suggest the raisins and fizzy water/lemonade. kids love this and they get quite mesmorized. easy to explain as well

My kids loved the mentos/coke experiments, which they did outside in their English school. In the US they have just done a similar, but less mess one. Put some baking soda (I think this is bicarb in the UK) in a balloon (not blown up). Put some vinegar in the bottom of a large plastic bottle. Put the balloon securely on the top of the bottle, and then shake the soda down. You get a lot of fizzy froth, and the gas blows up the balloon.

Thanks everyone for your ideas. She's got lots to think about now!

Martianbishop - please could you explain how mentos / coke works, and the difference between respiration and breathing? (You're way better than those New Scientist books )

OK mentos first.

Rather like the raisins thing, the surface of the mento has lots of minute dips and scratches. The makes the CO2 suddenly come out of solution, the gas expands and the fountain of coke shoots into the air.
You can make more of a splash with a calgon tablet......that does the same.. Plus the calgon reacts with the acid in the coke and makes even more CO2!

Acid + carbonate -> CO2 + Water + salt

Re breathing. We think of breathing and respiration as being the same. In biology they each have specific meanings. Breathing is the exchange of gases, ie getting the air into and out of your lungs. All living things respire and this is a chemical reaction that is happening in our cells all the time.

Glucose + O2 -> CO2 + H2O is the reaction.

If you reverse it you have the equation for photosynthesis. The secret of life on a Monday afternoon....not bad, eh?

sorry not read all through so apologies if I double anything already said. But how about the shelling of a raw egg in a jar of vinegar?
you put the vinegar in the glass jar, put in a whole raw egg in its shell, then watch.
The acid in the vinegar eats away the egg shekk because the shell is calciferous and so is alkali (sorry if I use the wrong word/ reason I'm a parent not a science teacher) and the acid reacts with it.
The entire egg remains intact in the vinegar with no shell on.

MB - thanks!

I get respiration (should have had you teaching my GCSE biology class - my teacher was rubbish!)

Why do mentos make a fountain when raisins just bob though? Raisins are much more pitted... Doesn't the sugar play some part? I remember when I was a kid and we had a sodastream - if you put the concentrate in before you fizzed the water, it gushed everywhere - I thought the mento thing was a similar principle?

For anyone else who still cares, I googled this - apparently I was wrong and it's nothing to do with sugar - it's all to do with the surface-tension-lowering properties of the aspartame (in the coke) and the gum arabic (on the surface of the mento) and the relatively high density of the mento.

New Scientist story here

Isn't science great!