My Science School

If two solutions of different concentrations are separated by a semi-permeable membrane (that is, a membrane that allows some substances but not others to pass through), the water from the weaker solution will start moving into the stronger solution. This is the process of osmosis.

 The flow will continue till the solutions on both sides have the same concentration. When grapes are put in the thick sugar syrup, the skin of the grapes act as a semi-permeable membrane and water from the grapes moves into the sugar syrup. The grapes shrivel up as a result.

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Try it with a rubber band. Stretch a rubber band and quickly hold it against your cheek. It feels warmer. Usually when things expand, a gas or liquid, for example, they become cooler.

When a liquid (or gas) expands, it takes the energy required for expansion from the liquid itself. So the liquid becomes cooler.

When a rubber band is stretched, it is not using up its internal energy. Energy is being supplied to it from the outside (by the one who is stretching it). So its internal energy increases and its temperature rises, making it slightly warmer to the touch.

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Find out from this experiment

If water is poured on a glass slab, the glass becomes wet; but if mercury is poured on the same glass surface it does not become wet. Why?

Whether a surface gets wet or not depends on

 1. The force of attraction between the molecules of the liquid and the molecules of the surface with which it is in contact, and

2. The cohesive force between the molecules of the liquid.

In the case of mercury, its molecules hold on tightly to each other. The molecules of the glass surface cannot pull them away. So the surface does not get wet.

In the case of water, the adhesive force is greater than the cohesive force between the water molecules. So the water clings to the glass surface, wetting it.

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It's time to clean your ceiling fan. But you'll find it's tough to clean the edges of the blades...

Static electricity develops on the blades of the fan when they are in motion, due to friction with the air. The static electricity attracts dust particles. As the edges of the blades are the first to come into contact with the surrounding air, more dust collects on them than on the other parts of the blades.

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Do you enjoy an aerated soft drink? Have you noticed that the content fizzes and gushes out when you open the cap?

If I take a soft drink bottle from the fridge and open it after shaking it vigorously, the liquid spurts out. Why does it come out so forcefully after shaking?

If the liquid rushes out when a softdrink bottle is opened, it is because carbon dioxide is escaping from the water in the drink.

Carbon dioxide is introduced into the water at high pressure and cold temperatures. Besides causing the liquid to bubble when opened, a little of the carbon dioxide reacts with water to form carbonic acid which gives the drink its refreshing tangy taste.

If you shake a bottle vigorously before opening it, some of the gas in the head of the bottle above the liquid will get dissolved in the liquid. This gas is more than the water in the drink can normally dissolve and so when the bottle is opened the sudden release of pressure will cause the gas to rush out. This will bring the liquid out in a gush.

Picture Credit : Google