Simple Machines Intro to Simple Machines Work Simple

Simple Machines Intro to Simple Machines & Work

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

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

Types of Simple Machines:

Examples: http: //staff. harrisonburg. k 12. va. us/~mwampo le/1 -resources/simple-machines/index. html n n n Bike Brake Lever n Bike Chain Pulley n Bike Tire Wheel & Axle n Bolt Screw n Bottle Top Screw n Broom Lever n Ceiling Fan Wheel & Axle n Clothes Pin Lever n Door Knob Wheel & Axle n Doorstop Wedge n Drill Bit Screw n Tap Wheel & Axle Hammer Lever Ramp Inclined Plane Light Switch Lever Paper Cutter Wedge & Pencil Lever Pliers Lever Pulley Scissors Lever Staplers Lever Slide Incline Plane Tape Dispenser Pulley

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

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

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

A camper uses a rope & pail to get water with a mass of 20 kg from a well. If it is raised a vertical distance of 3. 5 m, how much work is done by the camper? F=? d = 3. 5 m W=?

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

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

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

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

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