Now you see it ..

5th July 2013 at 01:00
... now you don't. Researchers recently made a goldfish and a kitten vanish. Explore the science of invisibility in your lessons

Most of us will have dreamed of having an "invisibility cloak" - a garment that would let us slip from sight, or even spy on others with impunity.

Now scientists in Singapore have unveiled new technology that has been used to make a kitten and a goldfish "disappear".

A video of experiments carried out at Nanyang Technological University shows a "cloak" made of thin panels of glass, suspended in a bowl of water. Plants in the bowl are clearly visible through the cloak but when a goldfish enters the cloak it disappears from view. Further footage shows the lower half of a kitten disappearing as it steps inside a cloak placed on a table (see images above).

The scientists have improved on earlier cloaks, which worked only with polarised light or microwaves. Although the devices are still fairly primitive, the hexagonal cloak used to conceal the goldfish can hide objects from six different directions. It could potentially be used in the security, surveillance and entertainment sectors.

The idea of an item of clothing that makes the wearer invisible has been around for thousands of years. Harry Potter inherits an invisibility cloak in the books by J.K. Rowling. But millennia earlier, in Greek mythology, the gods gave Perseus, the son of Zeus, a magical helmet that rendered him invisible, to help him in his task of slaying the Gorgon Medusa. Homer's The Iliad refers to Athena, goddess of wisdom and military victory, and patron of Athens, using the same helmet during the Trojan War.

So is reality catching up with mythology? The science of invisibility, also known as transformation optics, first drew international attention in 2006 when Sir John Pendry from Imperial College London, England, described how it would be possible to bend light around objects. Pendry says that the latest development is a "genuine step forward".

The experiments in Singapore were led by Baile Zhang, an assistant professor of physics and applied physics, who showed off a tiny invisibility cloak at a TED conference in February. Using a box of calcite - a cheap and abundant mineral that bends light - he made a rolled up piece of paper that had been submerged in oil vanish.

The science involved in these experiments will be challenging for young students. But you could use it to introduce them to the Greek and Roman gods, or to stage a role play based on who they would most like to disappear.


Why do some young children - and many animals - think that if they cannot see you, you cannot see them?

Who or what would you like to disappear and why?

How does some darkened glass allow people on the inside to look out but prevent those on the outside from looking in?

Why does the eye sometimes play tricks on us? Get students to consider three-dimensional images and films, and then look at the same subjects in two dimensions. What are the differences?

What would you do if you were given an invisibility cloak for a day?


Trick of the light

Staging scientific demonstrations as magic tricks can be an exciting experience for children - especially when they have to work out how you did it.

Try filling a large glass bowl with glycerin or cooking oil. Before the lesson, place a small test tube inside. The children won't be able to see the tube because the optical density (refractive index) of glass is similar to that of glycerin or cooking oil, so the light will bend (refract) very little when going from the oil to the test tube, rendering the test tube invisible.

While it is wrapped carefully in a cloth, smash an identical test tube with a hammer. This will be a shock but reassure the children that you can make it whole again with a special magic fluid. Then throw the pieces of glass into the bowl.

Get your students to say a magic chant as you use a pair of tongs to remove the undamaged test tube from the oil, to the amazement of all. If this doesn't impress them, nothing will.

For more information on this and other show-stopping feats, see the selection of science magic tricks from TES Connect science adviser Alessio Bernardelli. bit.lyscienceismagic


Telling tails

Animal-obsessed children may have wondered what life would be like if they had been born with a tail - or how different fashions would be if everybody had one.

Now an interactive app, A Cautionary Tail (pictured), tells the quirky story of a little girl born with a tail that expresses her emotions. The aim of the app is to help parents and teachers bolster self-confidence and positive body image in young children, and to reduce the bullying of those who appear to be a bit different.

Based on the award-winning short animation of the same name, voiced by Cate Blanchett, Barry Otto and David Wenham, the app from Australian company Rawr Media stars a child whose parents celebrate their daughter's unusual appendage.

Her tail also inspires exciting make-believe games with her friends. As she grows older, however, the young woman is bullied and rejected, and must choose between fitting in with the crowd and being true to herself.

The app has "Read to Me" and "Read on My Own" features, and suggested reading ages of 5-12.

For more information, go to


Can you believe your eyes? Test your students' perception skills in these optical illusion lesson starters from IBurchett. bit.lyvisualstarters

Encourage students to be kind and supportive in this lesson from Beatbullying. bit.lybullyproofshield

Experiment with instruction-writing skills in an invisible ink activity from rubyru22. bit.lyinvisiblemessage


Enchanting investigation

As the summer holidays approach, teachers will be looking for fun activities. Wave your wand - or marker pen - and make mathematics magical with this Harry Potter potion task.

Harry Potter has gone over to the Dark Side and created an evil potion to turn teachers into frogs. The key to the potion's success is the number of legs included from animals such as spiders, lizards and bats.

Challenge your students to work out as many ways as possible to create their potion. For example, it might require 64 legs, which would mean that they could use eight spiders (eight legs each), or four spiders and eight lizards (four legs each). Students will forget that they are using their multiplication and factors skills.

Record their findings in a table and conclude the investigation with some time for reflection.

Find the lesson at bit.lyharrypottermaths


Explore ancient mythology with JU3fromLeics' introduction to Greek gods. bit.lyGreeksOfOlympia

Take Harry Potter-themed mathematics further in this magical lesson on ratios. bit.lyhpratios

Banish confidence issues and build self-esteem in a superhero activity shared by greenteaaddict. bit.lysuperesteem

Watch and learn some wacky science tricks in this video from Teachers TV. bit.lymagicscience.

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