In an electric motor, periodically changing the direction of current in the electromagnet can cause the axle to spin because

a. the electromagnet loses its magnetism.
b. mechanical energy is converted to electric energy.
c. the force is constant.
d. the magnetic field reverses direction.

D The magnetic field reverses direction.

Explanation:

An electric motor works based on the principle of electromagnetic induction. It is the interaction of electric current and the magnetic field that makes a motor function.

An electric motor is a machine that will convert the electric energy to mechanical energy. In this a commutator is used to change the direction of current.

When the direction of flow of current is made to change, the magnetic field also reverses the direction.

There are different types of motors like AC motor,DC motor, Induction motor etc.

the independent variable, the one that is intentionally manipulated, is whether or not the car hits the barrier.

the dependent variable, the one that you measure the response in, is the distance that the washers travel.