Light travels in straight lines
Light is a form of energy that lets us see. One of its most important properties is that light travels in straight lines. We can show this by looking through three cards with holes: light only reaches your eye when all the holes line up in a straight line. Because light travels straight, an object in its path blocks it and forms a shadow.
Key idea
Light travels in straight lines and very fast (about 300 000 km per second). A straight beam of light is called a ray.
Sources and how we see
A luminous object makes its own light, such as the Sun, a lamp or a candle. A non-luminous object does not make light; we see it because it reflects light from a source into our eyes. The Moon is non-luminous — it reflects sunlight.
Other properties
Light can be reflected when it bounces off a surface, refracted when it bends on passing between materials, and split into colours by dispersion. Light can travel through a vacuum (empty space), which is how sunlight reaches the Earth.
Remember
- Light travels in straight lines and forms shadows.
- Luminous objects make light; non-luminous objects reflect it.
- Light can travel through empty space.