& Power

Is this kid working?

What about this? Does this look like work to you?

Work is done on an object if TWO things happen:

1. A force (push or pull) is applied to MOVE the object. 2. The direction of the object’s movement is in the SAME Direction as the force being applied.

Is this man doing work?

Is this man doing work? NO! Movement is not in the same direction as the force!

Is work being done here? movement force

Is work being done here? YES! Movement IS in the same direction as the force! movement force

How can you calculate the amount of work done in moving an object? * Work = force X distance Work (J) = force (N) X distance (m) Giving us units of Newton-Meters (N·m) We Express this as the JOULE (unit for work)

Energy: is the ability to do work

Remember To do work a force must be applied and an object must move. The greater the force that is applied that makes an object move, the more work that is done.

Which task would involve more work? A. lifting a shoe from the floor to your waist OR B. lifting a pile of books the same distance

Answer Even though the shoe & the books move the same distance, more work was done in lifting the books because it takes more FORCE to lift books. Hint: the books have greater ____? Mass

If you push on a wall are you doing work? If the wall doesn’t MOVE NO WORK HAS BEEN DONE

Power The rate at which work is done.

Power = Work (J) time (s) To Calculate Power: This is J/s or what we call Watts

Power If you were sanding a table by hand, you could increase your power using an electric sander to do the same amount of work in much less time.

Machine: Any device that helps make work easier

The work you do on a machine is called the Work Input The work you do on a machine is called the Work Input. The Work done by the machine is called the Work Output

Work input = Input Force Work Output = Output Force

Mechanical Advantage: Tells you how many times a machine multiplies force, the greater the MA is the easier work will be. Mechanical Advantage Output Force Input Force =

Force = work/distance Power = work/time = force x distance/time Work = distance x force Work = power x time Time = work/power Distance = work/force