In this article I am going to demonstrate how you the reader can bend steel without using any physical strength. So, strap yourselves and prepare for your minds to be blown.
Simply take a steel rod and dip it in a clear jar filled with water, and lo-behold you have it steel will be bent. Well, it will at least appear to be bent. This is not just true for steel but any other object that you can possibly dip in water. Go ahead and try it out with a spoon (or a pen) if you can’t do it with a steel rod and you’ll be amazed.
So why does this happen?
Well, remember how you were always taught light travels at the speed of 3000000 km/s (well 299792 km/s for all those science nerds out there). Yeah, turns out that is not entirely true. Light travels at various speeds in various mediums. The commonly known figure of 3000000 km/s is of that in vacuum. However, that figure can vary from medium to medium; i.e., light can have speeds slower or faster than that speed.
For example, the speed of light in glass is 200000 km/s. This is still extremely high but substantially lower than the speed in vacuum. This happens because each substance has a different refractive index which is a something like the resistance of that material. It determines at what speed light actually travels. This is called the refractive index of the substance denoted as R.I. The higher the R.I. of a substance the lower the speed of light in that medium meaning light faces more resistance moving in that substance.
The ratio of the refractive indexes is the inverse of the ratio of the speeds of light in those mediums. This is a direct consequence of Snell’s Law. And, explains why speed of light is different for different mediums.
Further, this difference in speeds of light causes light to bend more in one medium than another. This in turn causes a portion of the object to appear as bent thus producing the illusion. This is something that is very commonly observed in day to day activities.
Another very common illusion that is produced is if you place a coin at the bottom of a container filled with some liquid (water) with a R.I. the coin will appear to be raised above its actual level. This too is a direct consequence of refraction of light which makes the observer feel like the coin is displaced from its initial level to its new higher position.