12 interesting physics facts: light, sound and gravity

Physics explains how the world works — why a ball falls down, how sound reaches us, why a rainbow forms. Instead of fearing the formulas, start understanding physics through these interesting facts.

Gravity and motion

1. You would be lighter on the Moon: the Moon's gravity is about one-sixth of the Earth's. If you weigh 60 kilos on Earth, a scale on the Moon would show about 10 kilos — while your mass stays the same.
2. Escape velocity: to break completely free of the Earth's gravity, an object needs a speed of about 11.2 kilometres per second. That is why spacecraft are launched on powerful rockets.
3. The Earth is a giant magnet: the movement of molten iron inside the Earth creates a magnetic field. This is why a compass needle points north–south.

Sound

1. Sound is faster in water: sound travels at about 343 metres per second in air, about 1,480 in water and about 6,000 in steel. The closer the particles, the faster the sound.
2. Measure how far the lightning is: light is much faster than sound, so we see the flash first and hear the thunder later. Count the seconds between the flash and the thunder and divide by 3 — the lightning struck about that many kilometres away.

Did you know? A whole class of particles is called "bosons" in honour of the Indian physicist Satyendra Nath Bose.

Light

1. The bent pencil in water: a pencil standing in a glass of water looks bent, because light changes direction as it passes from air into water. This is called refraction.
2. Mirage: the "water" you see far ahead on a road in summer is also refraction at work — layers of hot air bend the light from the sky.
3. The seven colours of the rainbow: raindrops split the Sun's white light into seven colours — violet, indigo, blue, green, yellow, orange and red (VIBGYOR).
4. The Raman effect: C. V. Raman discovered that part of the light passing through a transparent substance changes its colour (wavelength). For this he won the Nobel Prize in Physics in 1930 — the first Asian to win a Nobel in science.

Heat and energy

1. Absolute zero: the lowest possible temperature is −273.15 degrees Celsius, called "absolute zero". Reaching it is considered impossible.
2. Hot air rises: when air is heated it expands and becomes lighter. Hot-air balloons fly on this principle.
3. Energy is never destroyed: energy can be neither created nor destroyed — it only changes from one form to another, such as electricity into light and heat.

How to make physics easy

Find the everyday event behind every formula — a bicycle, a fan, a pressure cooker, the kitchen stove: all are examples of physics. Do small experiments at home (with an adult watching) and write the results in your notebook.

Read more: Science questions · Class 5 quiz: the solar system.