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# 08/01/2013

Mel finds out about the art of drinking tea, plus Dick and Dom are back with more science experiments in 'How Dangerous Is Your House'.

1 hour

## Last on

Tue 19 Mar 2013 16:00

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## Activity 1: Make a Thaumatrope

A thaumatrope is an optical illusion which can also tell us something about what happens in our brains when watching television.

You will need:

• a piece of A4 card
• scissors
• pens for drawing
• 2 large elastic bands
• hole punch

Take the card, and draw a circle. You may wish to draw around something like a mug. Then, cut it out. Next, think of a pair of images that go together, such as a bird in a cage, or a fish in a bowl. On one side of your card, draw the cage (or bowl). Turn your card over, and on the other side, draw the bird or fish to go inside. This image needs to be upside down in relation to your first picture.

Using the hole punch, make a hole on either side of your pictures, near the edge of your circle. Take your elastic bands and thread one through each hole, and back through itself to tie a knot. Now, hold the elastic bands in each hand, stretched out, and twist your card around and around. It may be easier to ask someone to twist while you hold the rubber bands. Then let go, and watch the pictures!

What's happening?

A thaumatrope, and television, both take advantage of something called persistence of vision. If images appear one after the other very quickly – faster than one-twentieth of a second, your brain fills in the gaps between them, and you see it as if it was a continuous image. So in your thaumatrope, the bird looks as if it is in the birdcage. On television, you are actually watching lots of still pictures, about sixty per second, appearing one after the other. But what your brain registers is a continuous moving image.

## Activity 2: Remote Control Reflections

Most lounges are full of remote controls, and you can have a bit of scientific fun with them.

First, try turning your television on just pointing the remote control at it as you normally would.

Next, turn it off, but point the remote at the ceiling? Did it work?

Try pointing the remote at various surfaces around the room, for example, the sofa, a window, the back wall, a family member. What do you notice about the surfaces which work?

What's happening?

You should find that the remote control works when you point it at a hard surface, such as a wall or ceiling, even if it's not pointing at the television. But if you point it at a soft surface, it doesn't work. Remote controls work using infrared light, which we can't see. But it behaves in the same way that visible light does, travelling in straight lines. When you point the remote at a hard surface, such as the ceiling, the beam is reflected back into the room, and towards the sensor on your television. Soft surfaces absorb the infrared so there is no reflection.

If you have a couple of hand mirrors and some willing assistants, you can try making the beam from the remote control bounce between the mirrors, and turn the television on using reflection. How many mirrors can you manage?

## Activity 3: Couch potatoes

One danger of the living room is simply spending too much time in it! Getting enough exercise is important to keep your heart and lungs healthy.

Dick and Dom learn about the hazards of becoming a couch potato. And they find out what happens to their heart rates when they do some exercise – by taking their pulse.

You can find your pulse in places where an artery passes close to your skin.

Two good places are the underside of your wrist; or in the hollow area by the side of your neck. Use two fingers to feel your pulse – your thumb has a pulse of its own. Count how many beats you can feel in a minute, and write it down.

This is your resting pulse rate.

Now, do something active, for example, run or jump on the spot for a minute or two. Then, take your pulse again. Your heart rate will have gone up.

When you exercise, your muscles need more energy, which is carried in your blood. In order to get energy and oxygen around your body and to your muscles, your heart needs to pump more quickly, and so your pulse rate rises.