Intro to Simple Machines & Work

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

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

Types of Simple Machines:

Examples: Tap Hammer Ramp Bike Brake Bike Chain Light Switch Bike Tire http://staff.harrisonburg.k12.va.us/~mwampole/1-resources/simple-machines/index.html 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

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

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

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 = ?

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 = ?

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

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?

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.

(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

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

Homework: pg 293 Practice #1-4