PBS
Pbs Learning Media: Farmers in Peril
In this video from Wide Angle, the sparse life of the rural farmer in India is compared to the wealth of consumer goods available to wealthier city dwellers.
Wolfram Research
Wolfram Math World: Similar Triangles
Find the necessary information to decide if triangles are similar at this MathWorld site.
CK-12 Foundation
Ck 12: Math Grade 4
Browse resources related to fourth-grade math standards. Click on a topic for interactive lessons, videos, and extra practice.
BBC
Bbc: Gcse Bitesize: Why Do Scientists Think That Light and Sound Are Waves?
Light travels as transverse waves and can travel through a vacuum. Sound travels as longitudinal waves and needs to travel through a solid, liquid or gas. Read about the properties of light and of sound, and learn the differences between...