Mechanical Systems Unit Review

Early Machines machines help us do work and use energy more efficiently early machines were simple devices to help us do work such as: lift things, move things, crush things, or split things

Industrial Revolution now we had power such as steam, coal, oil… and we could improve the ability of machines to do work for us

Simple Machines levers winches incline planes wedges screws pulleys complex machines are several simple machines working together

Levers simple machine that changes the amount of force needed to move an object made up of a bar that is free to rotate around a fixed point called a fulcrum force exerted on the lever to make it move is the effort force the mass of the object being moved is called the load distance between fulcrum and load is called the load arm

E E E E = Effort Force L = Load F = Fulcrum L L L F F F 3 Classes of Levers

Winches consists of a small cylinder that has a crank or handle to produce effort force. axle of the winch acts like the fulcrum by exerting a force on the handle to turn the wheel the cable retracts the load

Incline Plane a ramp or slope that reduces the force needed to lift something it does this by increasing the distance over which the work is done

Screw its an incline plane that is wound around a central post helps to increase the force used –by rotating the screw, the incline plane pushes it forward (or into something), & the screw slowly travels a straight distance examples –screw –spiral staircase –jar lid

Wedge similar in shape to an incline plane works only in one direction when pushed into an object it gradually splits it apart –e.g. axe head splitting wood or a knife cutting something

Pulleys consists of wire, rope or chain moving on a grooved wheel designed to help lift large loads fixed pulley is attached to something that does not move (e.g. ceiling) moveable pulley is attached to something else, but the pulley can move

block and tackle uses a combination of fixed and moveable pulleys to make a “supercharged” system that can move very heavy loads when multiple pulleys are used in a system its called a compound pulley

Wheel and Axle combination of two wheels of different diameters that turn together –one is called the wheel… the other the axle –the longer the motion on the wheel… the greater the force on the axle… the more work gets done

Complex Machines several simple machines working together a system is a group of parts that work together to perform a function subsystems are usually simple machines linkages for the network or link between the subsystems so the system works

A Bicycle is a Complex Machine

Brakes in a Car are a Complex Machine

Gears gears are an essential component of most mechanical systems BECAUSE they transfer energy consist of a pair of wheels with teeth that interlink can be used to increase or decrease speed of the mechanical system can be used to change the direction of motion of the mechanical system

pinion A smaller gear (Y) is called a pinion. driving gear The gear that supplies the energy is called the driving gear (X). driven gear The gear to which the force is directed is called the driven gear (Y). A large gear (X) driving a smaller gear (Y) increases speed decreases torque and increases speed in the driven gear. multiplying gears Gears such as these are called multiplying gears. A small gear (Y) driving a larger gear (X) increases torque reduces speed and reduces speed in the driven gear. reducing gears Gears like these are called reducing gears. When the driving gear has fewer teeth than the driven gear, the driven gear then rotates more slowly than the driving gear. A car or bicycle in low gear uses reducing gears. When the driving and the driven gears are the same size they are known as parallel gears parallel gears.

Work work is energy in action –if there is no movement of object there is no work Work = Force x Distance –how much force was applied, and for how far work is measured in Joules (J) work input is the work you apply on the machine work output is the work the machine does on the load

Mechanical Advantage is a comparison of the force produced by a machine to the force applied to the machine (by you) Mechanical Advantage (MA) = Load force (F L ) or Output Force Effort force (F E ) Input Force or for levers, MA = effort arm load arm load force and effort force are both measured in Newtons (N), therefore MA has no units of measure MA can be 1

Mechanical Advantage - Pulleys to calculate the MA of a pulley, count the number of ropes/cables supporting the load

MA <1 when MA is >1 the machine is multiplying the input force to create a larger output force when MA is <1 it is useful for tasks that don’t require a large output force –e.g. a bicycle is a machine with a MA <1 the output force causes the bicycle to move faster than the rider could walk, so it is a very useful machine

Friction the difference between the calculated value and the real (actual) value of mechanical advantage is friction friction is essentially a force that opposes motion it is caused by the roughness of materials force is always needed to overcome friction –so the MA of the device will be less because of this added force that must be overcome friction in a system causes heat

Speed Ratio speed measures the distance an object travels in a given amount of time the measure of how a machine affects speed is called the speed ratio (SR) SR = input distance OR d input (m) output distance d output (m)

Efficiency efficiency is a measure of how well a machine or a device uses energy –the more energy that is lost, the less efficient a machine is –friction is a main factor in loss of energy –efficiency is represent in %. Efficiency (%) = Mechanical Advantage X 100 Speed Ratio lubricants can be used to reduce friction and improve efficiency NO MACHINE CAN BE 100% EFFICIENT !!!!

Hydraulic Systems liquids are placed under pressure in a confined space –because they are relatively incompressible… the can transmit that pressure to do work… like lifting very heavy objects pressure in liquids is measured in Pascals (Pa): P = F/A –F is force (N) –A is area (m 2 ) Pressure Lift

Pneumatic Systems air or gas is placed under pressure in a confined space… operates essentially like a hydraulic system e.g. sand blaster, air gun, nail gun, jackhammer, hovercraft