Everyday science

Scattering of sunlight

Sunlight contains all colours. Air molecules scatter short blue wavelengths far more than red ones (Rayleigh scattering), so blue light reaches our eyes from all over the sky.

Light travels through more air

When the Sun is low, its light passes through much more air. Most blue light is scattered away before it reaches us, leaving the reds and oranges.

Refraction in raindrops

Sunlight entering raindrops is bent (refracted), split into colours (dispersion) and reflected back. You see a rainbow when the Sun is behind you and rain is in front. The colours are red, orange, yellow, green, blue, indigo and violet.

Refraction

Light bends as it passes from water into air because it travels at different speeds in each. Our eyes trace the light in straight lines, so the stick seems bent and pools look shallower than they are.

Training the immune system

A vaccine contains a weakened, killed or harmless piece of a germ, or instructions to make one (mRNA). The immune system learns to recognize it and makes antibodies and memory cells, so it can fight the real germ quickly later.

Antibiotics kill bacteria, not viruses

Colds and flu are caused by viruses. Using antibiotics when they are not needed helps bacteria become resistant, making future infections harder to treat.

The body fighting infection

The brain's hypothalamus raises the body's temperature to help the immune system fight germs. Normal body temperature is about 37 °C (98.6 °F).

Ice is less dense than water

When water freezes, its molecules form an open crystal shape that takes up more space, so ice is about 9% less dense. This keeps lakes from freezing solid, protecting fish in winter.

Higher pressure raises the boiling point

Trapped steam increases the pressure inside, so water boils at about 120 °C instead of 100 °C and food cooks faster. At high altitudes water boils below 100 °C, so cooking takes longer.

Evaporation takes heat away

When sweat evaporates it absorbs heat from the skin. Sweat evaporates slowly in humid weather, which is why humid heat feels worse.

Condensation

At night surfaces cool down. Water vapour in the air touching them cools and condenses into droplets. A cold glass of water 'sweats' for the same reason.

Light travels faster than sound

Light travels at about 300,000 km per second, sound only about 343 m per second. Count the seconds between flash and thunder and divide by 3 to estimate the distance in kilometres.

No path for current

Current flows only when there is a difference in voltage. A bird touching one wire is at the same voltage everywhere, so no current flows through it. Touching two wires or a wire and the ground is deadly.

Earth's tilted axis

Earth is tilted about 23.5°. As it orbits the Sun, each hemisphere leans towards the Sun for part of the year (summer) and away for the other part (winter). Seasons are not caused by Earth's distance from the Sun.

Earth spins on its axis

Earth rotates once about every 24 hours. The side facing the Sun has day, the other side night. The Sun appears to rise in the east because Earth spins from west to east.

The Moon's gravity

The Moon's gravity (and to a lesser extent the Sun's) pulls ocean water into bulges, giving most coasts two high and two low tides a day.

Shadows of the Moon and Earth

A solar eclipse happens when the Moon passes between the Sun and Earth (at new moon). A lunar eclipse happens when Earth's shadow falls on the Moon (at full moon).

Gases trap heat

Gases such as carbon dioxide and methane let sunlight in but trap some of the heat Earth gives off. This keeps Earth warm enough for life, but extra gases from burning fossil fuels are causing global warming.

Blocks harmful ultraviolet rays

A layer of ozone gas about 15–35 km up absorbs most of the Sun's harmful UV radiation. CFCs damaged it, creating the 'ozone hole', until they were banned by the Montreal Protocol.

Pollution trapped near the ground

In winter a layer of warm air can sit above cooler air near the ground (temperature inversion), trapping smoke from vehicles, factories, brick kilns and crop burning. The result is thick, harmful smog.

Making water molecules vibrate

Microwaves make water molecules in food vibrate rapidly, which produces heat. Metal reflects microwaves and can cause sparks, so it should not be put inside.

Moving heat out

A refrigerant liquid evaporates inside the fridge, absorbing heat, and is then compressed and condensed in the coils at the back, releasing the heat into the room.