Does light travel in a straight line?
Take 2 pipes, one straight and one bent. Look at the flame of a burning candle through both the pipes separately.
We notice that we can see the flame through the straight pipe.
Looking at a flame through a straight pipe
But we cannot see the flame through the bent pipe. We can use pipes having different kinds of bends, the result will be the same.
Looking at a flame through a bent pipe
This proves that light does not bend, but travels in a straight path.
How does the straight-line path of light form shadows?
When an opaque object is kept in the path of light, light does not curve around the object. This is why a shadow is formed.
Formation of shadows due to the straight-line path of light