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

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

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

5. 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!!!

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

7. Simple Machines (Making work easier…phew!)

8. 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

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

10. 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

11. 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 N
Mechanical Advantage = 3

12. 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.

13. 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?

14. 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%

15. 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.

16. 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)