Science facts

Science facts: all 14, explained

1. Old church windows are not thicker at the bottom because glass flows.

   Glass is an amorphous solid and does not flow noticeably over centuries. Uneven old panes came from how glass was made at the time, and glaziers often fitted the thicker edge at the bottom.

   Source: Glass (Wikipedia) · Fact card

2. Water expands when it freezes.

   Most liquids shrink as they solidify, but water expands by about 9% as it forms ice, because its molecules lock into an open crystal structure. That is why ice floats and why frozen pipes can burst.

   Source: Ice (Wikipedia) · Fact card

3. Diamonds and pencil lead are made of the same element.

   Both diamond and graphite are pure carbon. In diamond, each carbon atom bonds tightly to four others in a rigid 3D structure. In graphite, the atoms form flat sheets that slide over each other, which is why it leaves marks on paper.

   Source: Allotropes of carbon (Wikipedia) · Fact card

4. Bananas are slightly radioactive.

   Bananas contain potassium, and a small fraction of natural potassium is the radioactive isotope potassium-40. The dose from eating one is tiny and harmless. Your own body contains potassium-40 too.

   Source: Banana equivalent dose (Wikipedia) · Fact card

5. Atoms are almost entirely empty space.

   An atom’s nucleus holds nearly all its mass but is tiny: if an atom were the size of a stadium, the nucleus would be about the size of a pea in the middle.

   Source: Atom (Wikipedia) · Fact card

6. Sound travels about four times faster in water than in air.

   Sound moves at around 343 metres per second in air and roughly 1,480 metres per second in water, because water molecules are closer together and pass vibrations on more quickly.

   Source: Speed of sound (Wikipedia) · Fact card

7. Helium makes your voice sound higher without changing its pitch.

   Your vocal cords vibrate at the same rate, but sound travels faster in helium, which changes the resonances of your vocal tract. That boosts the higher frequencies, so your voice sounds squeaky.

   Source: Helium (Wikipedia) · Fact card

8. Eiffel Tower grows taller in summer.

   Iron expands when it heats up, so the Eiffel Tower can grow by up to around 15 centimetres on a hot summer day.

   Source: Eiffel Tower (Wikipedia) · Fact card

9. Helium was discovered on the Sun before it was found on Earth.

   In 1868, astronomers studying sunlight during an eclipse saw a yellow line that matched no known element. It was named after Helios, the Greek Sun god, and found on Earth in 1895.

   Source: Helium (Wikipedia) · Fact card

10. Hot air balloons float because hot air is lighter than cold air.

    Heating the air inside the balloon makes it expand, so it is less dense than the cooler air outside. The difference creates lift, the same reason warm air rises in a room.

    Source: Hot air balloon (Wikipedia) · Fact card

11. Ordinary glass is made mostly from sand.

    Most glass is made by melting silica sand with soda ash and limestone. Lightning striking sand can also fuse it into natural glass tubes called fulgurites.

    Source: Glass (Wikipedia) · Fact card

12. Rainbows are really full circles.

    From the ground, the horizon cuts off the lower part, so we see an arc. From a plane or a high mountain, you can sometimes see a complete circular rainbow.

    Source: Rainbow (Wikipedia) · Fact card

13. Snowflakes almost always have six sides.

    The six-fold shape comes from the way water molecules link up as they freeze into ice crystals. Each flake grows differently as it falls through changing air.

    Source: Snowflake (Wikipedia) · Fact card

14. Light could travel around the Earth about 7.5 times in one second.

    Light moves at almost 300,000 kilometres per second in a vacuum. Earth’s circumference is about 40,000 kilometres.

    Source: Speed of light (Wikipedia) · Fact card