Plug one end of the bottle with your hand, then turn the bottle upside-down and rotate it hard. Remove your hand and watch the water pour out into the sink. The water will come out in a fast stream, rather than a slow glug-glug.

Water for heat storage

A large body of water will absorb heat energy quite slowly. It will also release this heat energy slowly, so it takes a long time to cool down. The high heat capacity of water has many uses. Since the earliest times, water has been used to keep homes cool in summer. For example, people would take blocks of ice from lakes in the winter and pack them away in sawdust and then use them to cool food during the summer. Now that way of producing energy are becoming more expensive, many small scale heating and cooling projects are being developed all around the world.

Scientists are developing ways of storing the heat energy of summer sunlight and using it for winter heating. In the United States, the University of Massachusetts at Amherst is building a central solar heating plant designed to capture the heat energy of the sun and to store it in the ground for use later in the year. During the summer months, south-facing solar collectors will absorb the heat energy and transfer it, via a heat exchanger, to a mixture of water and alcohol (the alcohol acts as an antifreeze). The warm water and alcohol mix is pumped through thousands of plastic pipes sunk deep in the ground, releasing heat energy that warms the clay soil. By midsummer the clay will reach temperatures of 50°C (122°F ) or more. Some heat energy will be diverted to a spare water tank to provide hot water at night when the solar collectors are not working. During the winter months, cold water flowing from the clay. The warm water will be circulated around pipes in the university buildings, keeping them warm.