Light does change its direction when it travels from one medium to another, a phenomenon known as refraction. Refraction occurs due to a change in the speed of light as it passes through different materials, such as air, water, or glass, which have different refractive indices.
When light travels from one medium to another at an angle, its speed changes, and this change in speed causes the light to bend or change direction. This bending of light is governed by Snell's law, which states that the angle of incidence (the incoming angle of the light ray) and the refractive indices of the two materials determine the angle of refraction (the bent path of the light ray).
However, when light travels from one place to another within the same medium, such as through air or a vacuum, it does not experience refraction because the speed of light remains constant. In these cases, light travels in a straight line without changing its direction.
It's important to note that although light may not change its direction within a single medium, it can still be influenced by other factors such as scattering, absorption, or reflection, which can alter its path or interaction with the surrounding objects.