Ms. Wickersham. Concepts o All mechanical devices that humans use are made from six basic building...

Ms. Wickersham

Concepts

o All mechanical devices that humans use are made from six basic building blocks called simple machines.

o It's important to note that when a simple machine is used the same amount of work is require. o A SM reduces the amount of effort needed to move

an object, but it results in moving it a greater distance to accomplish the same amount of work.

o All complex mechanisms are made from simple machines.

Simple Machines

Simple Machines: A simple device that provides a mechanical advantage, such as a wheel & axle, lever, pulley, or inclined plane.

Compound Machines: A system of two or more simple machines (the game mouse trap is a great example).

LEVER AND FULCRUM

PULLEY

WHEEL AND AXLE

INCLINED PLANE

WEDGE (Modification of Inclined plane)

SCREWS (Modification of Inclined plane)

THERE ARE SIX SIMPLE MACHINES

Machines do work for us.What is Work?

In order for work to be done, two conditions must be met:

o a force must move an object some distance

o and the force and distance the object moves must also be in the same direction.

Therefore, if the object does not move, no work is being done.

Formula for Work

In order to calculate work you need to have the measurement for Force and Distance.

W=F x D W = Force (Newtons) x distance (meters) W = Force (lbs) x distance (feet)

http://www.youtube.com/watch?v=pDK2p1QbPKQ

How do machines help us do work?

Mechanical advantage (MA) is the factor by which a mechanism multiplies the force put into it, making work easier.

Machines provide us with MA in the followingways:o A machine can increase the force o A machine can change the direction o A machine can increase the speed

LEVER AND FULCRUM

o A simple machine consisting of a rigid bar and a fulcrum (pivot point).

o There are three classes:o 1st classo 2nd classo 3rd classo http://www.youtube.com/watch?

v=Us2KfO_yrPA

Three classes of Levers

o The class of lever is determined by what is located in the middle.

o Use this diagram to help you remember.

o 1st class - fulcrum (pivot point) is in the middleo 2nd class - resistance (load) is in the middle o 3rd class - effort (force) is in the middle

FIRST CLASS LEVER

1st class-the fulcrum is between the effort and the Load.

The closer the load is to the fulcrum, the less effort needed to lift the load.

SECOND CLASS LEVER

2nd class- the LOAD is between the effort and the fulcrum.

THIRD CLASS LEVER

o These levers are used least often because their MA is less than 1.

o This means the force needed to use them is greater than the force they can move.

3rd class- the EFFORT is between the Load and the Fulcrum

How to calculate MA for levers:

Can be calculated in two ways:

If you know the distanceMA = Effort Arm

Resistance Arm (distance between the fulcrum and the input force)

If you know the weightMA = Load/Resistance Effort

PULLEY

o Pulley: A simple machine consisting essentially of a wheel with a grooved rim in which a pulled rope or chain can run to change the direction of the pull and thereby lift a load.

o http://www.youtube.com/watch?v=9T7tGosXM58

Pulley Systems

There are three types of pulley systems:

1. A FIXED PULLEY

2. A MOVABLE PULLEY and

3. A COMBINATION PULLEY

To calculate MA, you count the # of wheels

or ropes, excluding the effort rope.

FIXED PULLEY

A fixed pulley is “fixed” to something such as a ceiling, it cannot move.

Work: changes the direction of the force

A fixed pulley doesn't reduce the effort.

MA = 0

MOVABLE PULLEYS

A movable pulley is “movable” either vertically or horizontally.

Work: changes the direction of the force

MA = A movable pulley provides a mechanical advantage of 1.

COMBINATION PULLEY

A combined pulley is a combination of the fixed and movable, sometimes called a block and tackle.

Work: changes the direction of the force

MA = weight/# of pulleys

WHEEL AND AXLE

Wheel and Axle: a simple machine consisting of two concentric wheels.

Work: Increases the speed and changes direction

MA = wheel diameter/axle dia.

http://www.youtube.com/watch?v=XlZYPFDjTJM

INCLINED PLANE Inclined plane: A simple

machine used to raise or lower a load by rolling or sliding it instead of lifting it vertically.

Work: Increases the force

MA = Slope / height

http://www.youtube.com/watch?v=pG_kT565-XQ

WEDGES

o A piece of material, such as metal or wood, thick at one edge and tapered to a thin edge at the other

o The wedge is an inclined plane.

o MA = side length/thickness

o The screw is an incline plane that is wrapped around a central axis.

o The distance between the ridges is called the pitch (the distance advanced in a single turn).

o MA = dia. of screw/lead of screw

Mechanical Advantage

http://www.youtube.com/watch?v=rvscbkd3AzU&playnext=1&list=PL4S_gOG2-Y-hmAZqrMBtD5bqFcP3rBmkp&feature=results_main