What best describes why the critical angle of an air-glass boundary is 39.3°?

Awind turbine is initially spinning at a constant angular speed. as the wind's strength gradually increases, the turbine experiences a constant angular acceleration 0.173 rad/s2. after making 2870 revolutions, its angular speed is 132 rad/s. (a) what is the initial angular velocity of the turbine? (b) how much time elapses while the turbine is speeding up?

How is the gravitational force related to the distance between two objects?

When you push downward on a book at rest on a table, you feel an upward force. does this force depend on friction? defend your answer.