Foundations of Technology

 Common components (levers, inclined planes, wedges, wheels and axles, pulleys, screws, gears, cams, linkages, shafts, couplings, cables, bearings, brakes, clutches)

Table of simple mechanisms, from Chambers' Cyclopedia, Simple machines provide a "vocabulary" for understanding more complex machines

Class 1 - The fulcrum lies between the effort and the load Class 2 - The fulcrum is at one end, the effort at the other end and the load lies between the effort and the fulcrum Class 3 - The fulcrum is at one end, the load at the other end and the effort lies between the load and the fulcrum The ideal mechanical advantage (IMA) - ignoring internal friction - of a lever depends on the ratio of the length of the lever arm where the force is applied divided by the length of the lever are that lifts the load. The IMA of a lever can be less than or greater than 1 depending on the class of the lever.

(1) L e = 1.5, L r = 1.5 IMA = 1 (2) L e = 2, L r = 1 IMA = 2 (3) L e = 3, L r = 1 IMA = 3 (4) L e = 1, L r = 3 IMA = 1/3 (0.33) (1)(2) (3) (4)

N = Normal force that is perpendicular to the plane m = Mass of object g = Acceleration due to gravity θ (theta) = Angle of elevation of the plane, measured from the horizontal f = frictional force of the inclined planeNormal forceMassgravitythetafrictional force To calculate the forces on an object placed on an inclined plane, consider the three forces acting on it. The normal force (N) exerted on the body by the plane due to the force of gravity i.e. mg cos θnormal forcegravity the force due to gravity (mg, acting vertically downwards) and the frictional force (f) acting parallel to the plane.frictional force

The ideal mechanical advantage (IMA) of an inclined plane is the length of the incline divided by the vertical rise, the so-called run-to-rise ratio. The mechanical advantage increases as the slope of the incline decreases, but then the load will have to be moved a greater distance. Again, work in equals work out in an entirely efficient system. Friction will be large if objects are slide along the surface of the inclined plane. Efficiency can be increase by using rollers in conjunction with the inclined plane. L = 2 L = 4 h = 1 IMA = L/h IMA = 2IMA = 4 (1)Force needed to move 100lbs would be 50lbs, but you have to travel twice the distance. (2)Force needed to move 100lbs would be 25lbs but you have to travel four times the distance.

The wedge is an adaptation of the inclined plane. It can be used to raise a heavy load over a short distance or to split a log. The ideal mechanical advantage (IMA) of a wedge depends on the angle of the thin end. The smaller the angle, the less the force required to move the wedge a given distance through, say, a log. At the same time, the amount of splitting is decreased with smaller angles.

A windlass, a well known application of the wheel and axle. The ideal mechanical advantage of a wheel and axle is calculated with the following formula: RW = 3 RA = 1 RW = 4 RA = 5 IMA = 3 IMA = 4/5 (0.8)

The weight lifted divided by the lifting force is defined as the advantage of the pulley system.

The ideal mechanical advantage (IMA) of a screw is ideally the ratio of the circumference of the screw to the distance it advances during each revolution. A screw's lead is defined as the linear distance the screw travels in one revolution (360°). The lead determines the mechanical advantage of the screw; the smaller the lead, the higher the mechanical advantage. The pitch of a screw is defined as the distance between adjacent threads. In most screws, called "single start" screws, which have a single helical thread, the lead and pitch are equal.leadpitch A jackscrew, such as those used to raise homes and other structures, combines the usefulness of the screw and the lever. The lever is used to turn the screw. The mechanical advantage of a jackscrew is quite high. IMA = P

The cam and follower is a device which can convert rotary motion into linear motion (movement in a straight line). A cam is a specially shaped piece of material, usually metal or hard wearing plastic, which is fixed to rotating shaft. The cam can have various shapes eg. round, oval, heart shaped. A follower is a mechanism which is designed to move up and down as it follows the edge of the cam. Many machines which have moving parts use cams. A good example is the motor car engine which has cams to open and close valves and contact breaker points and operate fuel pumps. The exact distance it moves depends on the shape of the cam and this is know as a the throw The cam and follower is a device which can convert rotary motion into linear motion (movement in a straight line). A cam is a specially shaped piece of material, usually metal or hard wearing plastic, which is fixed to rotating shaft. The cam can have various shapes eg. round, oval, heart shaped. A follower is a mechanism which is designed to move up and down as it follows the edge of the cam.

 Basic system design (sketching, symbols, notation) Systems design is the process of defining the architecture, components, modules, interfaces, and data for a system to satisfy specified requirements. One could see it as the application of systems theory to product development.

 Simple controls (Complex systems may have layers of controls. Some controls operate particular parts of the system and some control other controls. Even the most fully automatic systems require human control at some point.)

 System performance evaluation (mechanical advantage, efficiency)  Safety considerations

 Force  Motion  Energy  Work  Power  Efficiency  Gravity  Friction

 Force – A push or pull exerted by one object on another.  Energy – The ability to do work. Energy is one of the basic resources used by a technological system.  Work – The transfer of energy from one physical system to another, expressed as the product of a force and the distance through which it moves a body in the direction of that force.

 Power – Force over time. Measured in foot- pounds, Newton meters, or watts.  Efficiency – Operating or performing in an effective and competent manner with a minimum of wasted time, energy, or waste products. The ratio of output work to input work  Friction – A force that opposes the motion or intended motion of a body in contact with another body.

 Gravity - An attractive force acting at a distance between two or more masses.  Motion - In physics, motion is a change in position of an object with respect to time.