Students use a spring scale to drag an object such as a ceramic coffee cup along a table top or the floor. The spring scale allows them to measure the frictional force that exists between the moving cup and the surface it slides on. By...

With a simple demonstration activity, students are introduced to the concept of friction as a force that impedes motion when two surfaces are in contact. Then, in the Associated Activity (Sliding and Stuttering), they work in teams to...

In this intimate talk filmed at TED's offices, energy innovator Amory Lovins shows how to get the US off oil and coal by 2050, $5 trillion cheaper, with no Act of Congress, led by business for profit. The key is integrating all four...