Unit 6 – Lecture 1

ReviewWork = Force * distance

measured in Joules [newton meters]this remains true using effort force

or resistance force

Power = Work / timemeasured in Joules per second

Mechanical Advantage = Force(out) / Force(in)

Efficiency = Work(out) / Work(in) * 100

MachinesA 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 MachinesThere are six types of simple machines:

LeverWheel-and-AxlePulleyInclined PlaneWedgeScrew

Helpful NoteALL 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 EfficiencyIdeal = according to the equationActual = taking into account the efficiencyex: MA = 2 but machine only has a 94%

efficiency2 = the ideal MA2* .94 = actual efficiency. MA = 1.88

LeverA Lever is comprised of:

a bar (straight or curved)a fixed point called the

fulcrum on which the bar pivots

Bar

Fulcrum

LeverThe 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

LeverThe distance from the fulcrum to where the

resistance force is applied is the Resistance Arm.

Resistance Arm

LeverThere are three classes of levers:

class is determined by where the location of the effort force, resistance force (load), and the fulcrum

Lever1st class lever:

see-Saw (Teeter-Totter)prying up a lid by

pushing down on a barpairs: scissors, pliers,

hedgeclippers

Lever2nd class lever:

doorwheelbarrow armspairs: shears,

nutcracker

Lever3rd class lever:

NOTE: MA = < 1 effort increases to increase distance of

loadtweezers!anything you swing

bat, sword, stick, golf clubbrooms, rakes, mops

MALeverThe 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

PracticeWhat 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-AxleWheel & 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

PracticeWhat is the MA of a Wheel with a 50 cm

radius connected to an Axle with a 2.5 cm radius?

PulleyPulley - 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 = 1no

difference

MA = 2no

difference

MA = 3no

difference

MA = 4no

difference

PulleyThere are two types of pulleys

Fixeddo not move,

merely redirect force

Moveableattached to the object

being pulled and multiply forcerises and falls with the object

PulleyBlock and Tackle System - a multiple-pulley

system where large amounts of distance are converted into force.composed of a fixed pulley & a moveable

pulleyMA = number of supporting ropes

PracticeWhat is the MA of this pulley system?

2

What is the effort force?[give in pounds of force]35 lbs

PracticeWhat is the MA of this pulley system?

3

What is the effort force?[give in pounds of force]23.3 lbs

PracticeWhat is the Force Output of this pulley

system?50 N