Physical Science: Work

Work

Chapter 5.1

What is work?• You work on math problems.• You go to work.• Making a sandwich is work.• Taking out the trash is too much

work.• Doing your homework is work.

• What machines help us work?

In physics, work is:• *Work is a formula: W=Fd

• *W= Work; F= Force; d= distance

• *Example:

• *Moving an object with a force of one newton for a distance of one meter= one joule of work

• *A joule is a unit that measures work

Distance (m)

W = F x d

Force (N)

Work (joules)

Brainstorm using a circle map:

1. In the Center write: Work

2. In the circle write types of simple machines

3. In the frame of reference write down what work these machines do

Input and Output• *Input = how much force you put

into doing work

• *Output = how much work was done

• *The work output can never exceed the work input!

Work:

Efficiency• *Efficiency is the fraction of

incoming energy that goes into a process.

Examples: Fuel mileage, appliances and energy efficiency

*Efficiency

• What does it mean to be efficient?

• *In a very efficient machine, all or most of the work input becomes work output

• In other words…if five joules of work was used to lift a box, the box would move the equivalent of five joules output- nothing was wasted.

What about friction?

• *In the real world- Work Output is always less than work input.– WHY?

• *Forces like friction use up some of the input work– Example: wheel turning on an axle can

get very hot…when the wheel gets hot some of that input work is being converted to heat.

Friction

*What is Power?• *Power is the rate at which work

is done.P = W t Time (sec)

Work (joules)

Power (watts)

Power:

Power Demo

• These two people did the same amount of work.

•The difference is Power: One person used more Power and got the work done much faster

•A more powerful machine does the same amount of work in less time

Review:• Work = Force x distance

Your Turn…

• On your paper:–Look through Chapter 5, Section 1

Pg 85-90

–Add more information from this section into your notes.

(at least six items)

Practice:

• Skill Sheet 5-AExample:

• How much work is done on a 10 N block that is lifted 5 meters off the ground by a pulley?

Work = F x d

W = 10N x 5 meters = 50 newton- meters OR 50 joules

Remember: newton-meters = joules

Work

• Work = Force x Distance

• Work is only done when something is moved a distance in the direction of the force.