worknrg

Work, What is Work?

Mechanical work is done when something is moved through a distance.

Work is also considered to be the transfer of energy

Definition

Really good site with the ideas of work here

http://id.mind.net/~zona/mstm/physics/mechanics/energy/work/work.html

unit

The Unit of work is the Joule, named after James Joule

Work = Force x Distance

but only if the distance covered is in the same direction as the force applied pushes in.

No work is done in the direction perpendicular to the force

Therefore when climbing a stairs with a box, the distance is the height of the climb. We do not need to worry about the horizontal distance travelled, as there is no acceleration, and therefore no Force, in that direction. W = F x s = 0 x s = 0

F = weight = mg ..... W = mgh

Simple experiments.

Lets have a look to see how this equation actually works.

Appropriate calculations involving force and displacement in the same direction only.

http://www.seai.ie/Schools/Secondary_Schools/Subjects/Physics/Unit_1_-_Work/Sample_questions/

Lifts, escalators.

http://www.seai.ie/Schools/Secondary_Schools/Subjects/Physics/Unit_1_-_Work/Lifts_and_escalato

Question Time

Calculate the work done when a force of 10 newtons acts through a distance of 50 metres in the direction of the force.

A girl pulls a sledge a distance of 100 metres. If the force exerted by the girl is 80 newtons in the direction in which the sledge is moving, calculate the work done.

A car of mass 900 kg accelerates at 3 ms-2 from rest. How much work is done after it has travelled 100 metres?

Lets check the answers

http://www.sei.ie/Schools/Secondary_Schools/Subjects/Physics/Unit_1_-_Work/Sample_questions/

Now what if we have to lift a box?

It is obvious that it is easier to walk along for 100m than to go up 3m!

Why is that?

Is it beacuse of Gravity?

The Force that must be applied must move the mass against the acceleration that is gravity so the force must be the mass x gravity, the gravity is the acceleration in this case.

We already know that WghtMssGrav

http://www.sei.ie/Schools/Secondary_Schools/Subjects/Physics/Unit_1_-_Work/Lifts_and_escalators/