大象传媒

Why does everyone say you shouldn鈥檛 play with your food? Here are three ways to do just that 鈥� and learn about science at the same time 鈥�

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You might think you taste food with your mouth 鈥� but as you鈥檒l see, your nose has a very important part to play in the process.

You will need:

• Several different flavours of crisps (but not salt and vinegar). The crisps should all have the same texture, even though the flavours are different (to eliminate cheating!)
• A scarf to use as a blindfold
• A volunteer

First blindfold your volunteer and ask them to hold their nose. Pass them a crisp 鈥� but don鈥檛 tell them what kind. Ask them to chew on it and tell you what flavour it is. They probably won鈥檛 be able to.

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Ask them to release their nose, and see if they can tell you the flavour now. Chances are, with their nose unblocked they鈥檒l be able to do it 鈥�

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PS you can try an even simpler version of this experiment on yourself. Pinch your nose and eat a crisp. The crisp will feel like a crisp in your mouth, but it won鈥檛 taste of much. When you release your nose, suddenly the flavour becomes obvious. Pinch your nose, and the flavour disappears again.

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PPS you can also try this experiment with differently flavoured sweets.

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What鈥檚 happening?
The taste buds in your nose help you to taste food 鈥� but you need your nose too, because it鈥檚 the aromas from food that give us most of our sense of flavour. Normally, when you eat, these foodie aromas travel between your mouth and your nose and the flavour you taste is a mix of what both your mouth and nose have 鈥榯asted鈥�. This means that when you hold your nose, you stop some aromas from reaching inside it, and so you鈥檙e not getting as much 鈥榝lavour鈥� information as you usually do, which is why you can鈥檛 taste flavours as well as usual.

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Why doesn鈥檛 it work with salt and vinegar crisps? Is it because they are the 鈥榢ing of crisps鈥� as Dom suggested? Well, not necessarily! It鈥檚 because your taste buds are very sensitive to the sour flavour of vinegar, so even with your nose blocked, that鈥檚 one thing you can taste.

We need iron in our diet to stay healthy. The iron is used by our bodies to create a substance called haemoglobin, which is what gives blood its rich red colour, and helps to carry oxygen to every part of the body. If someone was lacking in iron, they鈥檇 be pale and tired, and might even faint.听

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Some breakfast cereaIs are fortified with iron 鈥� and this experiment demonstrates that the iron in cereal really is the same as the iron as you鈥檇 find in a metal object like a nail!

You will need:

• An iron-fortified breakfast cereal (check the ingredients list if you鈥檙e not sure)
• A mortar and pestle, or a coffee grinder
• A neodymium magnet also called a 鈥榬are earth鈥� magnet
• Cling film
• A piece of white paper

First, grind up a few handfuls of cereal. You can do this with your mortar and pestle, or if you want extra quick results, use a coffee grinder! Pulverise the flakes until they鈥檙e like very, very fine dust.

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Now cover the end of your magnet in cling film. The reason you鈥檙e doing this is so that any particles that end up attracted to the magnet can be lifted off it simply by unwrapping the clingfilm.

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Now take your magnet and stir it slowly through the pulverised cereal. Keep moving it in the powder until you see particles sticking to the magnet 鈥� this could take a while so be patient. When you鈥檝e picked up enough of it to get a good look at, carefully unwrap the clingfilm and drop the particles onto the piece of white paper. Now place the magnet under the piece of paper, and see if you can 鈥減ull鈥� the cereal powder around from underneath 鈥� If you can, that鈥檚 iron you鈥檝e got there, and it鈥檚 being attracted to your magnet, just like a nail normally is!

Believe it or not, it鈥檚 possible to pick up a bottle containing rice, using just a pencil 鈥� Here鈥檚 how!

You will need:

• A small drinks bottle. The neck of the bottle must be narrower than the body
• Enough (uncooked) rice to fill the bottle
• A pencil

Stab the pencil into the rice vertically and jab it quickly up and down several times. Suddenly, you should feel the rice 鈥榞rip鈥� 鈥� and then you鈥檒l be able to pick the bottle up off the table. Have patience, and keep going as this demo doesn鈥檛 always work straightaway 鈥� It鈥檚 cool when it does though!

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What鈥檚 happening?
This is a demonstration of friction. Jabbing your pencil into the rice causes the rice grains to move around a little so that more of their surfaces are in contact with each other and the pencil. The more surface contact there is, the more friction there is, which is the force that you feel as resistance, and is a force that can stop things from moving. All of a sudden the pencil will become effectively stuck due to this friction so you can use it to pick up the weight of the bottle.