Geekery

Jelly experiment

Posted on 01. Jun, 2009 by Jake.

Dave Ansell, kitchen scientist, explains the science of jelly.

His experiment is pretty straightforward: make some jelly, according to the manufacturers instructions and add a bunch of fruit. Leave to set.
Among the fruits they used were fresh and tinned pineapple. The jelly containing fresh pineapple didn’t set properly, while the tinned pineapple jelly set just fine.

This experiment is fun, but hardly spectacular.

The interesting bit is in the explanation.

How does jelly set? Jelly is made of strands of protein molecules, which become entangled when they cool. This surrounds the water to produce solid, if wobbly, jelly.

But some fruit contain enzymes which break down proteins. Our own digestive systems break down proteins in a similar way. These enzymes break down the protein fibers in the jelly into strands that are too short to tangle properly and to allow the jelly to set.

The canned pineapple, however, has been heated to preserve it (by killing any germs inside the tin). The heat also denatures the enzymes, making the canned pineapple suitable for jelly use.

Check out Ansell’s protease & pineapple illustrations to better understand the process.

In a future experiment, I will be adding large quantities of vodka to the jelly and then consuming the finished product. This is purely in the interests of science, and is recommended only for professionals. Do not try this at home, unless you really want to.

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Uri Geller – Eat your heart out!

Posted on 25. May, 2009 by Jake.

Experiment One: Static Electricity

In this experiment, we will bend water with just the power of our minds. And a nylon comb.

You will need: the aforementioned comb (and applied brain power) and a tap.

Turn the tap on so there is fairly low water flow. Run the comb through your hair repeatedly. If you don’t have hair, ask your girlfriend/nephew/suitably hairy dog.

Move the teeth of the comb (the bit that was running through your Labrador’s golden tresses) towards the water.

Watch the water bend!

Alter the conditions in various ways: adjust the flow of water, run the comb through your hair some more, maybe use a different comb. Note the changes.

The effect is, of course, the consequence of electricity generated by running the nylon through your hair and then stored, as static electricity, in the comb.

We’re used to the effects of static electricity on solid objects: sticking a balloon to your hair, for example. But there’s something surprising about seeing flowing changing course – especially as there’s nothing even touching the water.

A charged object (in this case the comb) attracts small particles (as oppositely charged particles will attract each other). In this case, the molecules in the water are attracted to comb. More precisely, what’s happening is that electrons in your hair are collected in the vinyl comb, making it negatively charged. The positive charge of the water is then attracted by the comb.
Experiment Two: Telekinesis

As in the previous experiment, turn the tap on so that there is a gentle stream of water. Picture the water curving gently. When this causes the water to move, click here, to enter professional sceptic James Randi’s ‘One Million Dollar Paranormal Challenge.

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Cash to burn

Posted on 20. May, 2009 by Jake.

Ask a friend (to be safe, try make it one you don’t really like) to lend you a R200 note. Any note will do, but the R200 will produce maximum impact. Now set the note on fire.

If all goes well, the cash will set alight without burning. If not, well 200 bucks is a small price to pay for expanding the sum total of human knowledge

For this experiment you will need a solution of half water and half isopropyl alcohol. If your local Woolworths has run out of isopropyl alcohol, you can use ethanol instead, which is available at most chemists. But you may need to experiment on paper first to get the mixture of ethanol and water just right.

Most importantly, you will need a large bucket of water.

Soak the note in the solution. Hold it in a scientifically approved mechanism for handling combustible materials (I’m thinking braai tongs).

Light the note.

Allow your audience to gasp in amazement and then quickly douse the flames.   

Either bask in approval or run, depending on the outcome of the experiment.

What’s happening?

Alcohol burns at a lower temperature than the paper note, while the vaporisation of the water protects the cash.

Remember, you’re playing with fire so be careful! Like this guy:

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Crystal Method

Posted on 11. May, 2009 by Jake.

It’s Turner Prize season in the UK. The prestigious contemporary art prize is one of the more controversial on the British culture circuit. Recent winners have included Martin Creed’s The Lights Going On and Off, which is a room with, er, the lights going on and off. Among the 1999 finalists was Tracy Emin’s unmade bed.

This year’s shortlist includes a really unexpected source of beauty. Roger Hiorns has created a breathtaking piece, Seizure, in which he has covered the walls and ceiling of a London flat with copper sulphate crystals. The whole apartment looks like it is made of sparkling dark blue precious jewels (check out these pics).

Hiorns’s crystal sculpture is epic and ambitious (he used 80,000 litres of copper sulphate solution) but there’s no reason you can’t recreate his effect on a smaller scale.

If, like me, you had a chemistry set as a kid (and if you’re like me, you probably never used it) you’ll remember that it included a little packet of copper sulphate. This is less common today, what with copper sulphate being poisonous and all.

But now that we’re responsible adults – or at least adults – it’s finally time to play with chemicals. Here’s a quick and easy recipe for making pretty blue crystals. It’s fun to do with kids, but be sure to supervise them closely. Prevent contact from skin and do not swallow.

Super Easy Method

• Pour copper sulphate solution into hot water
• Pour into a jar
• Wait a couple of days
• Enjoy your crystals

Easy Method

To create better quality crystals, you first need to create a seed crystal.

• Mix copper sulphate into hot water until no more will dissolve (to create a saturated solution)
• Pour a small amount of the solution onto a shallow dish
• Leave this undisturbed overnight
• You will find small crystals on the saucer. Select the best for use as your ‘seed’.

Growing your crystal

• Tie your seed crystal to nylon string (fishing wire is good – dental floss will do) or other suitable line
• Suspend the seed in a jar containing the rest of the copper sulphate solution
• Leave the crystal and solution somewhere where it will not be disturbed. Do not seal the jar
• Leave until satisfied.Enter your crystal into the South African Contemporary Art Awards.

Tip: If you see crystals  growing on the sides of the jar, transfer the solution to a new, clean jar.  Competing crystals will slow the growth of your primary crystal.

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The Aerodynamics of a Ping Pong Ball

Posted on 26. Feb, 2009 by Jake.

If you’ve ever wanted to make a ping pong ball levitate in mid air – this kitchen science is for you.

This week Derek and Hugh Hunt are with Nick and Christian from Norwich School trying to investigate how we can make something levitate without using dodgy magic tricks!

What you need?

• A ping pong ball
• A bendy straw or a hairdryer – This experiment works best if the nozzle on your hairdryer is about the same size as a ping pong ball. If it’s not try making a funnel with a drinks bottle. Another thing you could use is a vacuum cleaner with a “blow” setting. Make sure it’s on the “cool” setting!

What do you do?

1. Bend your straw into a right angle
2. Put the long end of the straw in your mouth and point the short end straight up.
3. hold the ping pong ball over the end of the straw
4. Blow quite hard and let go of the ball when you feel it lift.

or:

1. Switch your hairdryer on and point the air stream vertically upwards.
2. Try to balance the ping pong ball into the air stream.

 What may Happen?

The ball levitates in the air stream, a few inches above the straw or the hairdryer!

It will stay there even if it is bouncing around a bit. You can even tip the straw over a bit and have the ball stay on the air stream.

What is going on?

Normally the ball would fall down under gravity but because you are blowing upwards the air hitting the ball is pushing it upwards. However the ball doesn’t fall off the stream of air and if you feel the stream it feels very narrow and rounded, it ought to fall off, but for some reason doesn’t.

This is an example of what is called the Coanda effect. When fluids, including air (which is a form of fluid), flow over a curved surface they follow the surface and “stick” to it. You can also see the Coanda effect at work by dribbling water down the back of a spoon it will stick to the spoon and get deflected, as shown in the image on the left.

 (a)      (b)

(a) when the ball is in the centre the forces from the air going around both sides cancel out

(b) as the ping pong ball moves to the left, it drags the air stream in the same direction. The air stream exerts an equal and opposite force on it so it is pulled back towards the centre

In our experiment, if the ball is in the centre of the stream of air, the air will flow around it symmetrically and leave the ball moving in the  in the same direction as it met it.

However if the ball moves out of the centre of the air stream, say to the left, there is going to be much more air sticking to the right hand side than the left. this means that it will keep on sticking to the surface of the ball and get deflected to the left.

There’s a very important physical  law called Newton’s 3rd law of motion, which says that every action has an equal and opposite reaction, which means that if you push something it pushes back. So because the ball is pulling the air to the left, the air will pull the ball to the right. Moving it back into the centre of the air stream.

In fact you can even tilt the straw or the hair dryer  to one side and the ball will stay floating in the angled air stream, due to the Coanda effect.

What has this got to do with the real world?

It has many applications but one of the most important is making a plane fly. A plane is held up by it’s wings which are designed to deflect air downwards, so by an equal and opposite reaction the plane is pushed upwards.

It is quite obvious how the air flowing under the wing is deflected downwards – it hits a curved surface and as it can’t go through it it has to be deflected downwards. The air passing over the top however is also deflected downwards this time due to the Coanda effect, it sticks to the surface and moves down. So half of what is keeping you in the air is the Coanda effect.

Why does the Coanda effect make air stick to surfaces?

If a stream of air leaves a curved surface, it will tend to drag the stationary air just beyond the point it leaves, along with it.

This creates a slight vacuum which bends the air round along the surface making it stick. The vacuum also pulls the surface in the opposite direction creating the force on the ping pong ball or the wing.

However if the surface curves too sharply or the air is moving too quickly the vacuum gets so strong that it can pull air backwards into the gap, creating a swirl of air or a vortex. This is very wasteful of energy and when this happens to a wing it is known as a stall. The wing looses half of its lift and gains a lot of extra drag, neither are ideal when flying, and if this happens near the ground a crash is quite likely. 

More information on the aerodynamics of a ping pong ball and other experiments like this can all be found at The Naked Scientists.

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