How does a lie detector work, and what causes car sickness?

We explore the curious questions that science can answer

If you were strapped to a polygraph machine – would you feel nervous? (Getty/iStock)

How does a lie detector work?

Lie detectors work on the principle that anyone who’s lying will be nervous, and nervous people tend to produce more adrenaline, which makes their hearts beat faster, their skin temperature rise and makes them sweat more. A lie detector basically measures how these things change during questioning. However, people generally get nervous anyway if they’re being questioned, while some people can control their heart rate if they concentrate. So, lie detectors aren’t foolproof indicators of guilt.

Some microwave food containers seem to have metallic films on top of them. Isn't that dangerous, because metal things in microwaves cause sparks?

Metal containers can produce dangerous arcing in a microwave oven. However, many food packages actually contain thin films of metal that speed the cooking process. For example, new packaging techniques use polyethylene terephthalate (PET) film laminated to paperboard as a “heat susceptor” – a metallised film that absorbs microwaves, and becomes a miniature frying pan to brown or fry the foods in the package.

So yes, metal in sufficient thicknesses can cause sparking. But thin films can improve the cooking ability of the microwave.

How are plastic bags made?

All plastic bags and sacks are made by a process known as “blown film extrusion” in which the molten plastic is blown up like a balloon as it is stretched out to produce a continuous tube of the film. This film is flattened to make a continuous double layer – which is what makes new bags difficult to open sometimes. This is then printed, cut to the appropriate length and sealed, and a handle is cut out, all in one process which is continuously repeated to produce individual bags.

How do things rust?

To create rust you need water, air and (of course) iron. The reaction is complicated, but essentially the oxygen reacts with the iron, with the help of the water, to make a reddish compound called iron oxide. Be wary of “rustproof” treatments which challenge you to “paint a nail with this and then put it in a jar of water – it won’t rust!”

If you do this, try immersing an untreated nail too – that probably won’t rust either.

Why does metal feel colder to the touch than plastic when they are both at room temperature?

Your body temperature is about 37C, and room temperature is about 20C to 25C. This means heat from your body is transported to objects you touch. Metal conducts heat better than plastic, so it conducts that heat away from you into the metal more quickly than plastic does. If both materials were at body temperature (or rather, skin temperature) you would probably not feel a difference, since no heat would be transferred.

What causes car sickness?

Car movement is noticed by a part of your body called the inner ear. In your inner ear are three curved tubes called semi-circular canals.

If you are reading a book or looking at the inside of the car your eyes tell your brain that you are not moving but the little tubes in your ear (the semi-circular canals) tell your brain that you are moving. This confuses the brain and makes you feel sick. If you look out of the window of the car and watch things moving past you will make your eyes realise that you are moving and you won’t feel so ill.