Have you ever held up a shiny metal spoon in front of your face to see your reflection? And have you noticed that your reflection changes if you switch from looking at one side of the spoon to the other? Your face will be the right way up when you look at the back of the spoon but upside-down when you look at the bowl of the spoon.
The other morning, my elder daughter was studying her face in a spoon instead of using it to eat her breakfast. She noticed the change in her reflection when turning the spoon around and it got her thinking: Why am I upside-down on one side of the spoon? Why does a spoon work like a mirror? And why don’t I ever look upside-down in a mirror?
The answer to all these questions is physics, so let’s find out more…!
Let’s start by thinking about reflection and light. Light is a kind of energy that travels in waves from the Sun to the Earth. (Check out my earlier post on how light is made to find out more.) Light waves move in straight lines but if an object gets in their way, they either get soaked up (or ‘absorbed’) by the object or they bounce off it (get ‘reflected’).
A mirror is an object that can reflect light. The sorts of mirrors that we use day-to-day (for example, in our bathrooms) are made from flat pieces of glass that have been coated on one side with metal.
When you look at your reflection in a mirror, what your eyes see the light that is reflected off the mirror back towards your face. Your reflection appears to be ‘behind’ the glass in the mirror and it is the same size as you actually are. But your reflection isn’t exactly the same as the ‘real-you’ because that it has its left and right sides swapped over.
And most times, we want our mirrors to show a useful reflection that looks like ‘real-us’. But if we make mirrors that aren’t flat, we can create funny and strange reflections – you might have seen mirrors like this at the fun-fair or a science museum? Mirrors that have bumps and bulges in them change the way light is reflected and this changes what our eyes see.
So, what about the spoon reflection? Well, a shiny metal spoon can act like a mirror and reflect light. But a spoon has a curved shape – one side curves inwards (we call this ‘concave’) and the other curves outwards (we call this ‘convex’) – so it will make a strange reflection.
A convex mirror reflects light from a wide angle and allows you to see more things but the things you see will appear smaller than they actually are. You might find convex mirrors on cars to help drivers see things to the sides and behind them. Concave mirrors can do two tricky things – if an object is far away from the mirror, it will appear much bigger than it actually is; if an object is close-up to the mirror, the reflection will be small and upside-down. And this is what happens when you [look at yourself in the eating-side of a spoon(https://www.sciencefocus.com/science/why-is-your-reflection-upside-down-in-a-spoon/)!
For more information about how light waves and reflections work, you might like to check out this short video.