-: MAKING A HOVERCRAFT :-

It Is a science toy which works on the phenomenon of the surface tension of water. It makes use of mothballs, which weaken the pull of surface tension in the water close to them. The stronger pull of the surface tension in front of each mothball pulls the sticks and the snowman spins in a circle.      

MATERIALS REQUIRED

• Draw a small snowman on the paper, color it and cut it out.
• Cut a slice of the cork about 1 inch thick and take four rectangular pieces of light wood. Make a small notch in each piece of wood. Glue one mothball In each notch In such a way that their surfaces remain In touch with water.

• Attach four sticks to the cork such that they are in the shape of a cross. At the free ends of these sticks, attach one wooden piece with glue.
• Stick the snowman to the slice of the cork.

• Take a plastic tub and fill It with water. Now, put the snowman Into the tub of water and watch It. The whole assembly will spin around due to the surface tension of water.

-: DETERMINING THE SURFACE TENSION OF WATER :-

Surface tension is a force that occurs at the surface of a liquid. The surface of a liquid due to the inward pull of its molecules acts like a stretched elastic membrane. This membrane can support light objects. For example, a blade can float on the surface of water. You can measure the surface tension of water by this simple project.

MATERIALS REQUIRED

• To measure surface tension, you have to make a balance device. For making the balance, take a wooden block and glue a wooden strip at Its center. Make the beam of the balance by using another wooden strip and using a pin as a pivot. 

• Take the iron ring and make a small bag of cloth. Tie three threads to make a pan of the balance.
• Take the plastic sheet and put a tiny hole in the centre with a needle. Tie a knot in a thread and use it to suspend the plastic sheet from one end of the balance.

• Use small nails on the other end to balance the plastic sheet. 

• Now, bring the bowl full of water and put it under the plastic sheet in such a way that it just touches the surface of water.You will see that the balance is disturbed. 

•  Now, add small nails in the pan until the plastic sheet suddenly breaks away from the surface of water. This extra weight is nothing but a measure of the surface tension of the water - the force with which it attracts the plastic.
• You can repeat the experiment by using mustard oil, kerosene oil, alcohol, etc. instead of water and measure their respective surface tensions also. 

More Example :-

• A razor blade or a sewing needle can be made to float on the surface of water, although these things are heavier than water. Put the blade or needle on a piece of blotting paper and then place it gently on the surface of water in a glass. The blotting paper soon gets drowned into the water and the blade or needle remains floating on the surface of water. This is due to surface tension.

• The nib of a pen is slit at the tip to provide the continuous flow of ink by surface tension. 

-: MAKING A WEATHER-INDICATING FLOWER :-

The amount of moisture in the air, i.e. humidity, can be used as the basis for forecasting the weather. When the humidity is high, rain is likely, while a low humidity usually indicates a dry spell. This project is based on the colour change produced in cobalt chloride by the moisture in air.

• Take a small sheet of blotting paper and cut it in the shape of a flower.

• With the help of cotton thread and a sewing needle, tie it with the thin wooden stick.

• Now take about 20 gm of cobalt chloride from a chemicals supplier or from your laboratory and make a strong solution of it in water.

• Dip the blotting paper flower in this solution, then put the flower in a warm place to dry.

• Now, your weather-indicating flower is ready for use. If the colour of the flower becomes pink on some day, it indicates a storm; if the colour becomes bluish-pink, it indicates rain; and if the colour becomes light blue, it indicates dry weather.

-: MAKING A MODEL OF AN ELEVATOR :-

People are usually lifted to the tops of tall buildings by elevators or lifts. An elevator car is raised by a windlass that is turned by an electric motor. Tracks keep the car moving in a straight line. A weight balances the weight of the car so that it is easier to pull up the car. The motor of the elevator can turn the windlass either way. It can wind up the cable and raise the car. It can unwind the cable and let the car go down. Electric wires go from the car to the motor. A person in the car can make it go up, go down or stop by using switches in the car. You can make a model of an elevator as follows.

Materials Required

• Drive nails through spools into the wooden board.

Add caption

• Take a cardboard box, say a shoe-box, without the lid. Tie one string to the bottom of the box and two strings to the top of the box. This box will act as the car of the elevator.

• Slip the bottom string of the car over the spools marked 4, 3, 2 and 1. Wind the string several times around spool 2. Tie its other end at the top of the box.
• Run the second string from the top of the box over spoois 5 and 6 and finally fasten it to a weight of about 100 gm to balance the weight of the car.

• You can put two toys, one of a boy and the other of a girl, in the box as passengers. Then the windlass (spool 2) with your fingers . The car will go up and down. You can make this model more attractive by putting it in a model building constructed of cardboard.