'To Float Or Not To Float'

The effect of Brine
You need:

• table salt
• glass
• egg
• spoon
• water

What to do:

1. Fill the glass with water.
2. Carefully put the egg in the water.

What happens?
The egg sinks to the bottom of the glass.

                             

3. Take the egg out of the water.

4. Add 10 tablespoons of salt to water and mix until it is dissolved. Now you have made Brine (10% NaCl solution)

5. Put the egg in the water once more.

What happens?

The egg floats.

Reason:

This is because the egg is more dense than the water so it sinks to the bottom. The salt water (Brine) is more dense than clear water, and therefore it makes possible for the egg to float.

How to make a Periscope

You need:

• a piece of strong cardboard, 32cm x 50cm
• scissors
• sticky tape
• 2 handbag mirrors, 6cm x 10cm
• a ruler
• pencil
• 2 square pieces of cardboard, each 6cm x 6cm

What to do:

     1.Using the ruler, divide the cardboard into four equal parts, each 8cm wide. Draw around a 6cm square twice, as you see in the picture. Cut these squares out.

     2. Cut the 6cm square in half diagonally to make 2 right angled triangles.

     3. Place the triangle on the top strip of the paper, as shown in the picture.Draw a line along the  diagonal of the triangle and cut through it to make a notch. Do this again in the 3 other places shown in the picture. Fold the cardboard into shape. Join the sides with sticky tape.

      4. Slide the 2 mirrors through the notches.

      5. Get behind an obstacle (such as a wall, or a window sill) so that the periscope is sticking above your head.Look through the square at the bottom. Enjoy!!

What happens?

In the mirror inside the periscope you will see a reflected image of whatever is behind the obstacle.

Reason :

This is because the light which rebounds from the objects or people on the other side of the obstacle strikes the mirror at the top of the periscope. Because of the angle of this mirror, it is reflected in the bottom mirror. You can use your periscope to look at something without being seen - just like submarine crew who need to survey the sea  before coming up to the surface!

   

How to make a simple Telescope

You need:

• Two magnifying glasses
• Two cardboard tubes of different diameters
• Sticky tape

What to do:

1. Slide one tube into the other. Fix a magnifying glass at one end with sticky tape.
2. Look at the moon through the tubes, with your eye against the taped magnifying glass and holding the second glass at the other end. Make the tube longer and shorter and move the second glass until you get a clear image.

What happens?

Through the taped magnifying glass, you can obtain a closer image of the moon , but upside down.

Reason:

This is because the lens at the end make the rays of light from the moon converge and create the image inside the tube. The lens nearest to the eye enlarges this image and makes the moon appear closer. Refractor telescopes work in the same way, but these are much larger in order to show images which are not upside down.  

Why do some things float and others sink?

You need:

• modelling clay
• a beaker
• water

What to do:

1. Fill the beaker with water.
2. Mould the modelling clay into a boat and place it in the water.
3. Now roll the boat-shaped clay into a ball. Place it in the water.  

What happens?

The little boat settles on the top. The ball sinks to the bottom.

Reason:

If more water is displaced by the object, greater will be the thrust which the object gets towards the top. With the clay boat, a wide surface floats on the water and therefore it displaces more amount of water. Hence it gets an upward thrust which is sufficient to keep it afloat. Where as the clay ball displaces very little water. So the thrust which it gets is not enough to keep it afloat. This experiment shows that floating also depends on the shape of an object.