How fast would a coin dropped from the Eiffel Tower travel?

We explore the curious questions that science can answer

The Eiffel Tower stands 330m tall (Getty/iStock)

How fast would a coin dropped from the top of the Eiffel Tower be travelling by the time it reached the bottom? Could it hurt someone if it hit them?

A falling object doesn’t accelerate indefinitely. It speeds up until it reaches its “terminal velocity”, after which it will continue to fall at the same speed. A coin dropped from the Eiffel Tower has a terminal velocity of about 45 metres per second (about 100mph) – which would certainly cause some considerable damage to anyone unlucky enough to be hit by it.

When a budgie in a cage starts flying, what happens to the total weight of cage and bird?

The total weight, as measured by a weighing scale under the cage, would go down. When the budgie is on its perch, the total weight is a combination of the weight of the cage and the weight of the bird.

When the bird launches itself into space, its weight no longer has any effect on the scale the cage is on.

However, if the bird were to be in an airtight container (don’t try this at home), the weight would remain the same. This is because as the budgie beats its wings in flight, each stroke pushes down a column of air with the same weight as the bird.

How many slices of bread could you toast in a lightning strike?

One lightning strike is a billion kW – the power of about 800 million toasters; it could toast 1.6 billion pieces of bread. Of course, lining up all those bits of bread and turning them over after five milliseconds could be tricky. 

How long would it take something to fall to the bottom of the deepest underwater ocean trench?

The Marianas trench is 35,839ft, or 10,860m deep, and it would take about an hour for an object thrown overboard to fall right to the bottom.

In the film ‘Goldfinger’, one of the women was painted in a non-porous paint which killed her. Would this really happen?

Yes, for several reasons. First, the skin is important for temperature regulation. We sweat constantly: it evaporates and removes heat from our bodies. Blood flowing near to the skin also loses heat as it is cooled by contact with the air. Without these two mechanisms, the body would overheat and we would die.

Secondly, the skin can absorb substances applied to it – such as any toxins in a non-porous paint. These might be eliminated by the kidneys, or they might kill you. Thirdly, a non-porous paint would mean that the skin’s waterproof surface layer would get waterlogged (like wearing a non-absorbent plaster for a while) and so be liable to infection. It might even start to fall apart.

What is the speed of a bullet in a plane travelling at 1,000mph if the bullet leaves the barrel at 500mph?

If the bullet is fired forward then the speed to somebody standing on the Earth would be 1,500mph and if fired towards the tail, 500mph.

To everybody on the plane it would appear that the bullet was travelling at 500mph no matter which direction it was fired.