How light travels

Light is a wave that travels in straight lines. It can cross empty space, where there is nothing to carry it.

• Light is a transverse wave. Sound is a longitudinal wave. Like every wave, both carry energy, and both can be reflected or absorbed.
• Light does not need particles. It can travel through a vacuum, which is how sunlight reaches us across space. Sound cannot.
• Light is very fast. In a vacuum it travels 300 000 km every second, which is 300 million metres per second. That is about a million times faster than sound in air.
• Light travels in straight lines, so we draw it as rays: straight lines with arrows. It does not bend round an object that is in its way, and that is why there are shadows.