Work Energy Theorem Review

Rule 1

Work is done by a force on an object

• objects can not do work on something

• forces cannot have work done on them

Rule 2

For the same amount of work, the force and displacement must be inversely proportional

* applying a greater force over the same displacement increases the amount of work

Rule 3

If the force acting on an object results in zero displacement, no work is being done on the object, work = 0

• object is not in motion while the force is acting on it

• object returns to original position

Rule 4

If no forces are acting on an object, no work is being done

* REMEMBER: net force is not the same as no forces

Rule 5

If the force acting on an object is perpendicular to the displacement vector of the object, no work is done.

Rule 6

If the force component is in the same direction as the displacement, the work is positive

If they are in opposite directions, the work is negative

Work Equation

W = FdcosΦ

Newton’s First Law Conclusion

When object is at rest or moving at constant speed, total work is 0

Newton’s Second Law Conclusion 1

If displacement and acceleration are in the same direction, the object is speeding up and the total work is positive

Newton’s Second Law Conclusion 2

If displacement and acceleration are in the opposite directions, the object is slowing down and the total work is negative