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
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.
Power Demo• These two people did the same amount of work.•The difference is Power: One person used morePower and got the work done much faster•A more powerful machine does the same amountof work in less time
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-A Example:• 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.