light always travels in straight lines,but it sometimes bends when traveling through different mediums.what?

Answer 1

The bending of light when it passes through one medium to another is called refraction. The light bends because it passes from a less dense medium (air) to a more dense (glass or water for example) When the light is passing through air, since it is less dense it will travel faster, when it enters the glass which is more dense it will refract/bend beacuse it will change speed.
This is why if you prut a straw in a glass of water, the light is coming from the air (less dense) to the water (more dense) and the light will be refracted and that's why the straw will appear to be broken. hope this is not too confusing.

Answer 2

All you have to do is rememeber that light is a wave. One of the properties of waves is that they will travel at different speeds through different media or more precisely, matter with different densities. The bending you observe is due to the interface of one material, (air, glass, plastic, polycarbonates, etc) with another different material. At the interface, the light actually changes speed, faster in less dense stuff, slower in greater density stuff.

Ok, say you have a beam of light. Ok, Now here is my feeble attempt at equating this to something larger... Say you are driving a car at a constant power (Not speed!). You can drive quite fast on the pavement, which has a high density. The soft sand at the side of the road is quite hard to go fast in. So lets say you swerve off the road and your left tires hit the sand... They will immediately slow down, but the right side will still be going fast on the pavement. The result it that you end up turning onto the sand. Once all 4 tires are on the sand, there's no more jerk that takes the steering because all the wheels are on the same media. Now say you didn't correct your direction after going on the sand, and there is another stretch of pavement coming up that is parallel to the one you were just on. Your left tires hit the road first, catch some good traction and take off, while the right side is still slow in the sand. The result? The car is heading in the exact same direction (only on a parallel) as when you left the first road.

Now pretend the car is a light beam, the sandy area in between the roads is glass, and the roads themselves are a vacuum. In a vacuum, the speed of light is about 300,000,000 M/Sec. When approaching from an angle, as it hits the interface at the glass, the leading edge slows down (the speed of light in glass is roughly 75% of a vacuum) and the trailing edge stays at the same speed. This results in the bend you see. When the light hits the other side of the glass, it will reverse that action, speed up again and the beam will now be travelling along a parallel path.

This was a bit longer than I anticipated but hopefully it helps you understand what is going on.

:)

Answer 3

It bends at the interface between the two media. Someone else will explain that better. In the meantime, fill up a glass with water, and put a straw in it. Now look: where the straw intersects the water from above and below, it looks like it's broken!

We can use this to our advantage. Prisms bend light that way too, so we use them in binoculars.