Are there a million germs on a pinhead and why do ice cubes turn white?

We explore the curious questions that science can answer

Bacteria is all around us, including on pinheads (Getty/iStock)

Is it true that there are about a million germs on every pinhead?

Before we can answer this, we need to say what a germ is. Normally we say a germ is any living organism that we cannot see but that makes us ill. “Germ” is a general word which can describe a bacterium, a virus, or a fungus. It is true that there are probably a million bacteria on the head of a pin. Bacteria are all around us.

However, unless we stab the pin deep into an arm or a leg, these bacteria will not harm us.

If atoms are mainly space, why doesn't your hand fall through a table?

Everything around us is made of atoms – even the air we breathe. The difference between the air we breathe and a table is that the atoms are much more tightly packed in a table. So while you can pass your hand through the air – where you are essentially pushing atoms out of the way – you can’t put your hand through a table because the atoms can’t move out of the way. It’s like trying to walk through a tennis court filled with 100,000 tennis balls as opposed to one with 100 tennis balls – you just can’t do it.

But it’s not just the space that’s a problem. There are also very strong forces holding atoms together. So although atoms are mainly space, the forces holding them together and the tightness with which they are packed mean you can’t put your hand through a table.

Why is it so difficult to iron out a crease when it's so easy to make a crease?

The Home Laundering Consultative Council says it’s all to do with the direction in which the fabric fibres are lying. The fibres prefer to be in straight lines and when you iron in a crease you align them in that way. It is quite easy to get the fibres to do what you want because they want to do it too!

However, because this is their preferred position, it is not easy to iron out a crease once it’s there. This involves making all the fibres jiggle up again. The best way to get rid of creases is to dampen the fabric so that the fibres relax and thus become easier to realign.

Why does a kettle go quiet just before it boils?

As water is heated, dissolved gasses in the water start to come out of solution. As water approaches boiling point all the dissolved gases have been released so there is no more bubbling. This is when the kettle goes quiet. As the water then begins to boil, the convection currents in the water become very violent and the water becomes noisy again.

Why doesn't lightning affect people inside a car?

There’s a special effect in a hollow sphere of metal, called a Faraday cage, where there isn’t any electricity inside the sphere. Faraday, the man who came up with lots of the rules on electricity which we now use, first found out that a hollow sphere has no electricity in it.

Why do you get dizzy when standing on top of a tall building?

For the same reason that you can easily walk along the edge of a pavement, but not along the edge of a chasm. Your eye is not used to seeing objects at a great distance where the floor should be. The perspectives that the brain expects are not there, and it causes the body to over-correct for the apparent discrepancy.

The resulting confusion in brain signals, and general anxiety caused by being in a potentially dangerous situation, cause dizziness.

Why do ice cubes go white?

When ice is made in a freezer, the freezing starts from different points within the cube, ie, the crystal structure of the cube isn’t uniform. When light enters it, you get refraction and reflection inside the cube so light doesn’t go straight through and the cube isn’t transparent.