Q10. Why do icebergs float in the sea?
Ans. WHEN MOST THINGS GET COLDER, THEY CONTRACT, AND WHEN MOST LIQUIDS freeze they get very much smaller. Water is unique in that it contracts only down to a certain temperature, 4oC (39.2oF). If it gets colder still, it begins to expand, because the special bonds between the hydrogen atoms in the water begin to break down. When it freezes, water expands so much that ice is actually Read More …
Q9. Who made the first waterwheels?
Ans. Nobody knows for sure, but wheels turned by water to generate power were described by Ancient Greek writers over 2,000 years ago.
Q8. What is hydroelectric power?
Ans. Hydroelectric power or HEP is electricity generated by turbines by falling water. Typically, hydroelectric power stations are sited inside dams built to create a big fall or ’head’ in the water.
Q7. Why does sweating keep you cool?
Ans. Sweating keep you cool because sweat is nearly all water, and water needs warmth to turn to vapour- which we call ‘drying’. Watery sweat dries from the skin by taking warmth from the body. This makes the body cooler
Q6. Why do plants need water?
Ans. Plants contain an even higher proportion of water than the human body. Plants need water for building cells, and also for transporting nutrients from the roots to the leaves where they are needed.
Q5. How much water is there in the body?
Ans. Water is found in nearly every cell of the body, which is why human bodies are almost three-quarters water. Women’s bodies have slightly less water than men’s, and children’s bodies slightly less than women.
Q4. What is heavy water?
Ans. Heavy water is deuterium oxide, water that is a little heavier than ordinary water because it contains the hydrogen isotope deuterium rather than ordinary hydrogen. Heavy water is used in the nuclear industry to slow down nuclear reactions.
Q8. What is an echo?
Ans. An echo is when you shout in a large empty hall or in a tunnel, and you hear the noise ringing back out at you a moment or two later. The echo is simply the sound of the voice bouncing back from the walls. You don’t normally hear echoes, because they only bounce back clearly off smooth, hard surface and in confined spaces. Even in a confined space, the walls must be at least 17 meters (55 ft) away, because you will hear an echo only if it bounces back at least 0.1 second after you shouted.
Q7. What is sound frequency?
Ans. Some sounds, like a car’s squealing brakes, are very high -pitched. Others, like a booming dash drum, are very low- pitched. What makes them different is the frequency of the sound waves. If the sound waves follow very rapidly one after another, they are high- frequency and make a high sound. If there a long gaps between each wave, they are low- frequency and make a low sound. A law frequency sound is about 20 Hz or waves per second. A high frequency sound is 20,000 Hz or waves per second.
Q6. How does sound travel?
Ans. Every sound is created by vibration, be it an elastic band twanging or a loud speaker cone shaking to and fro. But you can’t hear any sounds in a vacuum. This is because the sound reaches your ears as a vibration- and there must be something to vibrate. Normally, this is the air. When a sound source vibrates to and fro, it pushes the air around it to and fro.
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