## Resonance.

Q5. What is resonance?
Ans. If allowed to vibrate freely, every object always tends to vibrate at the same rate. This is its natural frequency. You can make things vibrate faster or slower than this by jogging them at particular intervals. But if you can jog it at just the same rate as its natural frequency, it vibrates in sympathy and the vibrations become much stronger. This is resonance.

## Why is the Earth like a magnet?

Q4. Why is the Earth like a magnet?
Ans. As the Earth spins, the swirling of its iron core turns the core into a giant magnet. It is a little like the way a bicycle dynamo generates an electric current. Like smaller magnets, the earth’s magnet has two poles, a north and a south. It is because earth is magnet that ball magnets always point in the same direction if allowed to swivel freely.

## Magnetic Pole.

Q3. What is a magnetic pole?
Ans. Magnetism is there invisible force that draws together some metals, such as iron and steel- or pushes them apart. This force is especially strong at each end of the magnet. These two powerful ends are called poles. One is called the north (or north-seeking) pole, because if the magnet is suspended freely this pole swing round until it points north. The other is called the South Pole. If the opposite poles of the magnets meet, they will be drawn together. If the same poles meet, the magnets will push each other apart.

## Lodestone.

Q2. What is a lodestone?
Ans. Thousands of years before people learned how to make steel magnets, they found that lumps of certain type rock can attract or repel each other, or bits of iron. These rocks are called lodestones, and contain iron oxide, which makes them naturally magnet.

## What is a magnetic field?

Q1. What is a magnetic field?
Ans. The magnetic field is the area around the magnet in which its effects are felt. It gets gradually weaker further away from the magnet. The Earth’s magnetic field extends some 80,000 km (50,000 miles) out into space.

## What is hydraulic power.

Q3. What is hydraulic power?

Ans. Fluids like water are in-compressible- that is, they cannot be squashed. So if you push fluid through a pipe, it will push out the other end. Hydraulic power uses fluid-filled pipes working like this to drive things very smoothly. Hydraulic means water, but most hydraulic systems sue oil to avoid rust problems.

## What’s so special about water?

Q2. What’s so special about water?

Ans. WATER IS SPECIAL IN MANY WAYS, AND IS ESSENTIAL TO ALL LIVING THINGS.

Water is chemically neutral, yet dissolves many substances, which is why it is so important for life. It is denser as a liquid than a solid and so expand when it freezes. Water is found naturally in all of its three states of matter-solid ice, liquid water and gaseous water vapour. This is unusual, because of the strong bonds between its two hydrogen atoms and one oxygen atom. Read More …

## Why do things float?

Q1. Why do things float?

Ans. When an object is immersed in water, the weight of the object pushes it down. But the water around it pushes it back up with a force equal to the weight of water displaced (pushed out of the way). The object sinks until its weight is equaled by the up thrust, then floats.

## What is half-life?

Q10. What is half-life?

Ans. No-one can predict when an atomic nucleus will decay. But scientists can predict how long it will take for half the particles in a substance to decay. This is its half-life. Stronium-90 has a half-life of 9 minutes. Uranium-238 has a half-life of 4.5 billion years.

## Who invented the atomic bomb?

Q9. Who invented the atomic bomb?

Ans. The first atomic bombs were developed in the USA towards the end of the Second World War by a brilliant team of scientists under the leadership of Robert Oppenheimer (1904-1967). His colleagues included Leo Szilard (1898-1964) and Otto Frisch (1904-1979). Together they created the first two A-bombs, which were dropped on Hiroshima and Nagasaki in Japan in 1945 with devastating effect.