Explain why both a power source (like a battery) and a complete circuit are necessary for an electromagnet to function. 

Fill in the blank. the number of each type of element in the compound (other than 1) is represented by a small number to the right of the element symbol.

Askydiver weighing 140 lb (including equipment) falls vertically downward from an altitude of 19,000 ft and opens the parachute after 18 s of free fall. assume that the force of air resistance, which is directed opposite to the velocity, is of magnitude 0.55|v| when the parachute is closed and is of magnitude 14|v| when the parachute is open, where the velocity v is measured in ft/s. assume that acceleration due to gravity has magnitude 32 ft/s/s; remember that weight is the product of mass and gravitational acceleration. (a) find the speed of the skydiver when the parachute opens. (b) find the distance fallen before the parachute opens. (c) what is the limiting velocity vl after the parachute opens? (d) determine how long the sky diver is in the air after the parachute opens. (e) plot the graph of velocity versus time from the beginning of the fall until the skydiver reaches the ground.

You can watch static electricity in action by rubbing an inflated balloon against your hair. your hair will actually stand on its end! it does this because each hair becomes charged, and they all repel one another.