1. Intro to Simple Machines & Work

2. Simple Machines: Are devices used to make work easier Used to:
change the size of the force
change the direction of the force
change the speed or distance of the force
Rarely 100% efficient

3. Types of Simple Machines:
Six diff types grouped into two categories:
Lever
Pulley
Wheel & Axle
Inclined Plan
Screw
Wedge

4. Types of Simple Machines:

5. Examples: Tap Hammer Ramp Bike Brake Bike Chain Light Switch Bike Tire
Tap
Hammer
Ramp
Light Switch
Paper Cutter
Pencil
Pliers
Pulley
Scissors
Staplers
Slide
Tape Dispenser
Wheel & Axle
Bike Brake
Bike Chain
Bike Tire
Bolt
Bottle Top
Broom
Ceiling Fan
Clothes Pin
Door Knob
Doorstop
Drill Bit
Lever
Lever
Pulley
Inclined Plane
Wheel & Axle
Lever
Screw
Wedge & Lever
Screw
Lever
Lever
Lever
Wheel & Axle
Pulley
Lever
Lever
Wheel & Axle
Lever
Wedge
Incline Plane
Screw
Pulley

6. Work: An applied force acting through a distance
Force & motion must be in the same direction
Applied force must cause motion for work to be done
Work measured in J (Joules) & is scalar m J N

7. Ex. Pushing against a wall = NO work
Carrying books while walking = NO work on books
Lifting your backpack from the floor = WORK
Going up stairs = WORK

8. Ex #1
How much work is done by a boy pushing a car with a force of 800N for a distance of 200m?
F = 800N
d = 200m
W = ?

9. Ex #2
A camper uses a rope & pail to get water with a mass of 20kg from a well. If it is raised a vertical distance of 3.5m, how much work is done by the camper?
F = ?
d = 3.5m
W = ?

10. Ex #3
A boy pulls a sled with a rope. The rope makes an angle of 20̊ with the ground. The force in the rope is 300 N. The boy moves the sled 30 m. How much work is done?
20o
300 N
Δd = 30 m
Force = Direction of Motion H O ? A

11. Ex #4
A 1000kg car accelerates uniformly from rest to a speed of 20m/s in 16s. How much work is done by the engine during this time?

12. How Simple Machines Work
The machine does not allow you to do less work, but does allow you to do the work using a smaller force.
Since the work that you do is the same or greater, the force must be applied through a greater distance.

13. (Fd) Effort = (Fd) Resistance
Work done
by you
Work done
to the object =
*(ignoring friction)*
(Fd) Effort = (Fd) Resistance
Note: The force and the displacement must always be in the same direction

14. Effort Force: Resisting Force: Effort Distance: Resistance Distance:
The force a person puts into the machine
Resisting Force:
The force that must be overcome to do the work
Effort Distance:
The distance through which the effort force moves
Resistance Distance:
The distance through which the resistance force moves

15. Homework:
pg 293 Practice #1-4