What is an axis? a felge? and arab spring

What happens to light waves from a star as the star moves away from earth?

Which example has gravitational potential energy? a.a horse slowing down from a run b.an apple about to fall from a tree branch c.a bicycle being pedaled down a horizontal path d.beaker sitting on the floor

Automobile fuel efficiency is often measured in miles that the car can be driven per gallon of fuel (mpg). heavier cars tend to have lower fuel efficiencies (lower mpg ratings). which variable (weight or fuel efficiency) is most naturally considered the explanatory (predictor) variable in this context?