Simple Machines: Lever, Wheel & Axle, Pulley Unit 6 – Lecture 1

Review Work = Force * distance measured in Joules [newton meters] this remains true using effort force or resistance force Power = Work / time measured in Joules per second Mechanical Advantage = Force(out) / Force(in) Efficiency = Work(out) / Work(in) * 100

Machines A Simple Machine accomplishes the work in one motion. A Compound Machine is made up of two or more simple machines. Most machines are compound machines.

Simple Machines There are six types of simple machines: Lever Wheel-and-Axle Pulley Inclined Plane Wedge Screw

Helpful Note ALL of the equations for the mechanical advantage of different types of machines will be given to you for the test [which will take place tentatively on Monday, 2/8]. Ideal vs. Actual Mechanical Efficiency Ideal = according to the equation Actual = taking into account the efficiency ex: MA = 2 but machine only has a 94% efficiency 2 = the ideal MA 2* .94 = actual efficiency. MA = 1.88

Lever Bar Fulcrum A Lever is comprised of: a bar (straight or curved) a fixed point called the fulcrum on which the bar pivots Bar Fulcrum

Lever The distance from where the effort force is applied to the fulcrum is the Effort Arm of the lever. this is where your effort is done Effort Arm

Lever The distance from the fulcrum to where the resistance force is applied is the Resistance Arm. Resistance Arm

Lever There are three classes of levers: class is determined by where the location of the effort force, resistance force (load), and the fulcrum

Lever 1st class lever: see-Saw (Teeter-Totter) prying up a lid by pushing down on a bar pairs: scissors, pliers, hedgeclippers

Lever 2nd class lever: door wheelbarrow arms pairs: shears, nutcracker

Lever 3rd class lever: NOTE: MA = < 1 effort increases to increase distance of load tweezers! anything you swing bat, sword, stick, golf club brooms, rakes, mops

MALever The MA of a lever is calculated as: MALever = Effort Arm Resistance Arm (again, both in units of length, so there are no MA units) The longer the effort arm, the more the MA [the better it is for you] recall: increase distance, less force

Practice What is the MA of a lever with an Effort Arm of 6 m and a Resistance Arm of .3 m? Which type of lever does not increase the force output of the machine? If a lever has a MA of 9, and a force of 6 N is applied, how much force will the lever apply?

Wheel-and-Axle Wheel & Axle - a simple machine made of two circles of different diameters that rotate together. The outer circle (wheel) is turned with less force over a larger distance so that the inner circle (axle) turns with more force over a shorter distance. Ex. Steering wheels, door knobs, faucet handles

MAWheel&Axle MA = radiusWheel radiusAxle Explains how to steer larger vehicles with less force

Practice What is the MA of a Wheel with a 50 cm radius connected to an Axle with a 2.5 cm radius?

Pulley Pulley - a simple machine comprised of a wheel with a rope or chain running around it. The MA of a pulley system is equal to the number of ropes which support the object, because the weight is distributed. MA = 1 no difference MA = 2 no difference MA = 3 no difference MA = 4 no difference

Pulley There are two types of pulleys Fixed do not move, merely redirect force Moveable attached to the object being pulled and multiply force rises and falls with the object

Pulley Block and Tackle System - a multiple-pulley system where large amounts of distance are converted into force. composed of a fixed pulley & a moveable pulley MA = number of supporting ropes

Practice 2 What is the effort force? [give in pounds of force] 35 lbs What is the MA of this pulley system? 2 What is the effort force? [give in pounds of force] 35 lbs

Practice 3 What is the effort force? [give in pounds of force] What is the MA of this pulley system? 3 What is the effort force? [give in pounds of force] 23.3 lbs

Practice What is the Force Output of this pulley system? 50 N