December 5, 2017 You need: Clean paper / pencil Warm Up: Mental Math Quiz. I CAN: define work, power, and simple machines

Early Release Guest speaker Cougar Mtn Teacher planning-PM Cougar Mtn Swag-Brrr

Formula for Work Work is measured in a unit called “Joules”

Main Concept 2: Power is ONLY about how fast work gets done! More or Less Power? Main Concept 2: Power is ONLY about how fast work gets done! It’s nice to get work done quickly! So here we have a certain amount of stacked wood. We need to cut it! We have several choices of tools we can use: “Power Saw” This saw will get the work done eventually, but it takes way too long to do it Since this saw does the same work faster than the hand saw, we say it has MORE POWER!!! OR Hand Saw Here’s the point: Both will get the same work done (cutting all the boards), but one will take less time = more power!!!

Power is measured in a unit called “Watts” Formula for Power Power is measured in a unit called “Watts”

Simple Machines (Making work easier…phew!)

How do machines do work? Machines make work easier by changing 3 things about the FORCE you exert to do work: AMOUNT OF FORCE you exert DISTANCE over which you exert force DIRECTION in which you exert force

What are SIMPLE MACHINES? There are only 6 basic simple machines that make work easier: Inclined Plane Wedge Screw Lever Wheel & Axle Pulley

What is the mechanical advantage of a machine? A machine’s mechanical advantage is the number of times a machine increases a force exerted on it. Mechanical = Output Force Advantage Input Force

What is the mechanical advantage of a machine? You exert 10 N of force on a can opener. The can opener exerts 30 N of force on the can. What is the mechanical advantage? Mechanical = Output Force = 30 N Advantage Input Force 10 N Mechanical Advantage = 3

What is the efficiency of a machine? The EFFICIENCY compares: the work you put IN to the work the machine puts OUT. An IDEAL machine is 100% efficient. INPUT WORK = OUTPUT WORK In the real world, some input work is always lost due to FRICTION between the moving parts of the machine.

What is the efficiency of a machine? EFFICIENCY = Output Work x 100% Input Work You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower?

What is the efficiency of a machine? You mow the lawn with a rusty lawn mower. You do 50,000 J of work on the lawn mower but only 25,000 J go to cutting the lawn. What is the efficiency of the lawn mower? EFFICIENCY = Output Work x 100% Input Work Efficiency = 25,000 J x 100% 50,000 J Efficiency = 50%

Test expectations Answers need to be written onto your scan-tron. When you finish, LOOK BACK OVER your answers. When you are truly finished, you may: draw/doodle, read silently, put your head down to rest. Remember that you are NOT to communicate with others during a test.

Progress Reports These are not permanent – merely a way to be sure that you and your folks are aware of what is getting done (or not getting done). Look for the missing work and/or go to Ms.Garris’s web page and print a new copy. Make up work is accepted – but it must first be done!! (Deadline = Dec.13th)