1. Today’s Agenda…
Bellringer: What conditions have to be met for something to be considered work?
Discuss Homework
Notes on Work and Machines
Simple Machines Chart
Quiz tomorrow…study friction, work, and machines!

2. Work and Simple Machines Study Pack #15

3. What is work?
In science, the word work has a different meaning than you may be familiar with.
The scientific definition of work is: using a force to move an object a distance (when both the force and the motion of the object are in the same direction.)

4. Work or Not?
According to the scientific definition, what is work and what is not?
a teacher lecturing to her class
a mouse pushing a piece of cheese with its nose across the floor

5. Work or Not?
According to the scientific definition, what is work and what is not?
a teacher lecturing to her class
a mouse pushing a piece of cheese with its nose across the floor

7. What’s work?
A scientist delivers a speech to an audience of his peers.
A body builder lifts 350 pounds above his head.
A mother carries her baby from room to room.
A father pushes a baby in a carriage.
A woman carries a 20 kg grocery bag to her car?

8. What’s work?
A scientist delivers a speech to an audience of his peers. No
A body builder lifts 350 pounds above his head. Yes
A mother carries her baby from room to room. No
A father pushes a baby in a carriage. Yes
A woman carries a 20 km grocery bag to her car? No

9. Formula for work Work = Force x Distance The unit of force is newtons
The unit of distance is meters
The unit of work is newton-meters
One newton-meter is equal to one joule
So, the unit of work is a joule

10. W=F x D Work = Force x Distance
Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done?

11. W=F x D Work = Force x Distance
Calculate: If a man pushes a concrete block 10 meters with a force of 20 N, how much work has he done? 200 joules
(W = 20N x 10m)

12. History of Work
Before engines and motors were invented, people had to do things like lifting or pushing heavy loads by hand. Using an animal could help, but what they really needed were some clever ways to either make work easier or faster.

13. Simple Machines
Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces.

14. Simple Machines The six simple machines are: Lever Wheel and Axle
Pulley
Inclined Plane
Wedge
Screw

15. Simple Machines
A simple machine is a device that helps make work easier by:
Changing the amount of force you apply
Changing the direction of the force you apply

16. Work In & Work Out
You have to do work on the machine – this is work in
Then the machine does work – this is work out
For example: You push on the handles of a can opener and they move; then the can opener does work as its blades move down and puncture the can

17. Work In & Work Out Work in = Work out in perfect machines
Remember, machines just make work easier!
But we have to remember the role of friction in a machine!

18. Work In & Work Out
Friction from two objects in a machine rubbing together will cause some of the work in to be turned to heat
Heat cannot be used to do work, so some of the work in is lost due to friction!
So in real machines work in ≠ work out!

19. Work In & Work Out
The best machines take this into account and try to reduce the friction as much as possible!
This makes the machine more efficient! So the amount of work out is closer to the amount of work in!

20. More About Simple Machines
Simple Machines Chart
Use pages 147 – 150 in your textbook
For each machine:
Explain how it makes work easier
Draw a diagram
Give at least 3 examples (try to give some from the book and some from your own examples)