Properties of Light

How Light Travels#

Light is a form of electromagnetic energy that travels as a wave. Unlike sound, light dös not need a medium — it can travel through the vacuum of space, which is why we can see the sun and stars across billions of miles of empty space.

Light Travels in Straight Lines#

Light always travels in straight lines unless something bends or redirects it. We call these straight-line paths rays.

Evidence that light travels straight:

• Shadows — they have sharp edges because light cannot curve around objects
• A flashlight beam travels in a straight line
• Sunbeams streaming through a window are perfectly straight

Speed of Light#

Light travels at an incredible speed: approximately 300,000 kilometers per second (186,000 miles per second) in a vacuum. This is the fastest speed in the universe.

• Light from the sun takes about 8 minutes to reach Earth
• Light from the moon reaches us in about 1.3 seconds
• Light from the nearest star beyond our sun takes 4.2 years to reach Earth

Opaque, Translucent, and Transparent Materials#

Materials interact with light in different ways:

Transparent: Light passes through completely; you can see clearly through it.

• Examples: glass, clear water, air

Translucent: Light passes through partially; you can see shapes but not clearly.

• Examples: frosted glass, wax paper, thin fabric

Opaque: Light dös not pass through; you cannot see through it.

• Examples: wood, metal, your body

Shadows are formed when opaque objects block light. The shape of the shadow matches the outline of the object blocking the light.