Why is it necessary to use at least one electromagnet in a motor instead of using only permanent magnets?

Because as you might already know electromagnets use a conductive metal and electricity to make the said electromagnet. So what do you get if you use the electromagnet and move it through coiled wire. The magnetism makes a electrical current thus making your motor.

I hope that this was helpful for you. :3  

I'm not sure what your asking buddy.. but i know that you can weld two peices of steel by pure force and pressure.

the best answer for these questions would be:

1.            c. is smaller

2.            d) concrete operational

3.            b) interaction with the environment – the children interact with their environment can them learn more.

4.            a) parents who reason openly with children can limit a child’s cognitive ability.