Science and Physics

Water boils at 100 degrees Celsius at sea level, but far lower high up a mountain.

Ice floats on liquid water because freezing makes it slightly less dense than the liquid.

Glass is sometimes called a slow liquid, yet it is a solid with a disordered structure.

Helium is the only element that refuses to freeze solid under ordinary atmospheric pressure.

Dry ice skips the liquid stage entirely and turns straight from a solid into a gas.

Salt lowers the freezing point of water, which is why it melts ice on winter roads.

Baking soda fizzes when vinegar is added because the reaction releases carbon dioxide gas.

Rust forms when iron meets oxygen and water, creating a flaky reddish compound over time.

Copper turns green with age as its surface slowly reacts with air and moisture.

Soap cleans by holding one end to water and the other end to greasy dirt.

Oil and water separate because water molecules cling to each other more than to oil.

Honey keeps for years because its low water content makes it a poor home for bacteria.

Yeast makes bread rise by releasing bubbles of carbon dioxide into the soft dough.

Boiling water bubbles are water vapor, not air, forming when liquid turns into gas.

Steam can burn far worse than boiling water because it carries extra hidden heat.

Metal feels colder than wood at the same temperature since it draws heat away faster.

Dark clothing absorbs more sunlight than pale clothing, which is why summer shirts feel hotter.

A microwave heats food by making water molecules inside it vibrate and warm their surroundings.

Refrigerators cool food by moving heat outward rather than by creating coldness from nothing.

Pressure cookers raise the boiling point of water so food cooks faster than usual.

Sound travels roughly four times faster through water than it does through ordinary air.

Sound cannot travel through a vacuum because there are no particles to carry the vibration.

Bats navigate dark caves by listening to echoes of their own high-pitched calls.

Thunder sounds after lightning is seen because light travels much faster than sound.

Mirrors reverse images left to right because they reflect light straight back at you.

A straw looks bent in water because light changes speed when it leaves the liquid.

Magnets attract iron but have no noticeable pull on wood, plastic, or glass.

Every magnet has a north pole and a south pole that cannot be separated.

Opposite magnetic poles pull toward each other, while matching poles push each other away.

Earth behaves like a giant magnet with magnetic poles near its geographic poles.

Static electricity builds up when two different materials rub together and trade electrons.

Balloons stick to walls after rubbing because static charge attracts the neutral surface.

Electric current flows in a loop, so a broken wire stops the whole circuit.

Copper wire is used in homes because it carries electricity with very little resistance.

Bulbs glow because a thin filament resists the current and heats until it shines.

Fuses protect houses by melting and breaking the circuit when too much current passes.

Batteries store chemical energy and release it as electricity when connected in a circuit.

A volt measures electrical push, while an amp measures how much charge flows.

The meter was originally defined as one ten-millionth of the distance from equator to pole.

A kilogram was once defined by a physical cylinder kept in a vault in France.

Celsius sets freezing at zero and boiling at one hundred for pure water at sea level.

Absolute zero is the coldest possible temperature, where particles nearly stop moving altogether.

An atom is mostly empty space, with tiny electrons orbiting a dense central nucleus.

Molecules in a gas move freely, while those in a solid only vibrate in place.

Density compares mass to volume, which explains why a small rock can feel heavy.

Dropped objects fall at the same rate regardless of weight when air resistance is removed.

Water expands as it freezes, which is why ice floats instead of sinking to the bottom.

A metal spoon feels colder than a wooden one at the same temperature because metal carries heat away faster.

A spinning wheel resists tipping over, which is part of why a rolling bicycle stays upright.

Glass is often described as a slow-moving liquid, but it is really a solid with a disordered structure.

Helium balloons slowly shrink because the atoms are small enough to escape through the rubber.

Static shocks build up when two different materials rub together and then suddenly discharge.