If you throw a ball through a pile of sand, it will slow down in the sand and emerge at less that its initial speed. But when light shines on a pane of glass, even though it slows down inside, its speed upon emerging is the same as its initial speed. Explain.

The phenomenon you are describing is related to the concept of refraction, which occurs when light passes through different mediums, such as air, glass, or water. Refraction is caused by the change in speed of light as it transitions from one medium to another.

When a ball moves through a pile of sand, it experiences friction and encounters resistance from the grains of sand. This friction slows down the ball's motion, causing it to emerge from the sand at a reduced speed.

On the other hand, when light passes through a transparent material like glass, it also experiences a change in speed. The speed of light is different in different mediums because it interacts with the particles of the material. In the case of glass, the speed of light is slower than in air.

When light enters the glass pane, it slows down due to this change in speed. The change in speed causes the light to slightly change direction, a phenomenon known as bending. However, when light emerges from the other side of the glass pane and re-enters the air, it returns to its original speed. This occurs because the properties of glass allow light to traverse the material without dissipating or losing energy.

In other words, light can maintain its initial speed upon emerging from a pane of glass because the structure and composition of the glass material do not impede or slow down the light significantly. This is different from the way a ball slows down in sand, as the friction and resistance of the individual sand grains result in a net loss of momentum for the ball.