All forces must have
and
oa) power, energy
ob) power, a direction
o a magnitude; energy
od) a magnitude, a direction

All forces must have  a magnitude and a direction.

Explanation:

If object A uses a force on object B, formerly object B must use a force of similar magnitude and opposing direction behind on object A.This law describes a certain proportion in nature: forces perpetually happen in pairs, and one group cannot use a force on different without enduring a force itself.

Sometimes lead to this law loosely as action-reaction, where the force exercised is the action and the force experienced as a result is the reaction. An example, rockets move forward by expelling gas backward at high velocity.

81 is a composite number.