UNIT 2: MECHANICAL SYSTEMS UNIT NOTEBOOK. SCIENCE 8 Mr. Anderson

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1 UNIT 2: MECHANICAL SYSTEMS UNIT NOTEBOOK SCIENCE 8 Mr. Anderson

2 Section 1 Notes 1.1 Simple Machines - Meeting Human Needs Machines help people use energy more efficiently. A machine helps us do work. The first machines were very simple devices. For example, early Egyptian builders used levers to move rocks and ramps to help them move large loads to higher levels. Each machine was designed to meet specific need. Although all these machines were different, they all had one thing in common: they required ANIMALS or HUMANS as their source of energy. The earliest machines were simple devices to make work easier; like moving a large rock or moving a load up an incline, splitting wood or lifting materials up to a working area above the ground. Meeting the Same Need In Different Ways In the past, one very common way of raising water from deep wells was to use a type of water wheel called a SAKIA (PERSIAN WHEEL). Persian wheels had a series of buckets attached to a long rope, draped over a large wheel. Animals such as donkeys, camels or cows turned the wheel, raising the buckets of water.

3 This device, called an ARCHIMEDES SCREW, can move large volumes of water or other substances quickly. Originally powered by hand, the are now powered by motors. Archimedes was only one of many famous inventors. Hundreds of years later, the famous Italian artist / scientists / architect / all-round-smart-guy Leonardo da Vinci designed water lifts using two Archimedes screws to raise water up a tower. Simple Machines A simple machine is a tool or device made up of one basic machine. There are six types of basic machines: 1. LEVER 2. WEDGE 3. INCLINED PLANE 4. PULLEY 5. SCREW 6. WHEEL AND AXLE

4 LEVERS Levers consist of the following parts: FULCRUM LOAD OR RESITANCE EFFORT OR FORCE Levers help us to use LESS FORCE when doing a task, like pulling out a nail, opening a bottle or hitting a baseball. There are three classes of levers. Sketch Examples CLASS 1 TEETER TOTTER SCISSORS CLASS 2 WHEEL BARROW CLASS 3 CATAPULT

5 INCLINE PLANE Inclined planes help us to move heavy objects HIGHER with LESS FORCE. We also call these RAMPS. WEDGE A wedge helps us to use force to SEPARATE an object. Wedges drive into objects quickly, normally in a DOWNWARD direction. SCREW A screw is essentially an INCLINED PLANE wrapped around an AXLE. A screw changes the ROTATIONAL (turning) energy into LINEAR (straight) energy.

6 PULLEY A pulley consists of a wire, rope or cable moving around a grooved wheel. Pulleys help to CHANGE the DIRECTION of the load and to lift large loads easily. WHEEL AND AXLE Normally a combination of two wheels of different diameters, a wheel and axle help you to INCREASE the amount of FORCE you put in, as well as increase SPEED or travelling distance.

7 Using these simple machines gives us an ADVANTAGE. There are four advantages that these simple machines can provide us (1) CHANGE IN THE DIRECTION OF FORCE (2) MULTIPLING THE FORCE (mechanical advantage) (3) INCREASING/DECREASING SPEED (speed advantage) Transferring force (staple remover) Change the direction of a force (a pulley on a flagpole) (4) TRANSFERING THE FORCE Modifying Simple Machines Simple machines provide us an Multiplying force (screwdriver) Increasing or decreasing speed (scissors) advantage when doing work. In what ways can we "modify" a simple machine to maximize the amount of effort or work it can do for us? Type of Machine Lever Changes for Less Effort Needed move the fulcrum closer to the load Incline Plane Decrease the slope / longer ramp Wedge Sharper wedge Screw Decrease the space between threads / have finer threads Pulley Add more pulleys Wheel & Axle Have a larger wheel and a smaller axle

8 1.2 The Complex Machine A Mechanical Team Complex Machines A complex machine is a device in which simple machines all work together. Complex machines can be made of two or more simple machines. SYSTEM: A group of machines or devices that work together to complete a task SUBSYSTEM: An individual device or part that has a specific function The bicycle is a good example of a complex machine because it is a system for moving a person from one place to another. Within the bicycle are groups of parts that perform specific functions, such as braking or steering. These groups of parts are the subsystems. Each subsystem in a complex machine contains a simple machine and usually has just one function. The subsystems of a bicycle are: Wheel and axle Gears Pedals Brakes & Steering

9 Subsystems That Transfer Forces The subsystems in a mechanical device that produce motion, such as in a bicycle, play a role in how energy is transferred within the system. The subsystems are called linkages and transmissions. Some complex machines use LINKAGES to move an object by TRANSFERRING ENERGY from an energy source. The linkage is the part that does the transferring of energy. Bicycle chains are a great example of a linkage. YOU are the energy source, and the WHEELS are the objects needing your energy. You use the linkage in your bike to TRANSFER ENERGY TRANSMISSIONS also transfer energy from an energy source to an object. They are a special type of linkage to transfer energy from the engine to the wheels. Transmissions like this one appear in vehicles and large trucks and semi-trailers. The larger the transmission, the larger the load (the more it can carry).

10 Gears Gears are ESSENTIAL COMPONENTS of most mechanical systems. They have a pair of WHEELS (sometimes more) with teeth that INTERLINK. DRIVING GEAR: the gear you turn DRIVEN GEAR: the gears that turn in the train In a gear system, one turning gear transfers ENERGY to the gear next to it. This is rotational energy into whatever we want! Gears are used for two reasons: Increase or decrease the speed of a machine How Gears Affect Speed A large gear driving a smaller gear decreases torque (twist) and increases speed in the driven gear. Gears such as these are called multiplying gears. A small gear driving a larger gear increases torque and reduces speed in the driven gear. 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.

11 2.1 Machines Make Work Easier Mechanical Advantage Machines can make work easier by increasing the amount of force that you exert on an object - but without making YOU work harder! When a machine increases the force that you exert on an object, we say that the machine creates a MECHANICAL ADVANTAGE. Mechanical Advantage: The amount by which a machine can multiply the force. Input force = force you apply Output force = force machine applies Quite simply, MECHANICAL ADVANTAGE is comparing how much force you put into the machine to the force done by the machine. (Size of the load compared to the effort force) Think of this example. What sort of advantage does the machine give you?

12 A lever will give you a HIGH mechanical advantage. This means that the LEVER will EXERT MORE FORCE than you will. What is something that you could change about the lever to INCREASE or DECREASE the mechanical advantage? What sort of advantage does this machine give you? How could you change this machine to INCREASE or DECREASE the mechanical advantage? A screw is an example of a machine that actually gives you a LOW mechanical advantage - you are working harder than the machine!! But there is a trade-off... A screw has a low mechanical advantage, but can INCREASE THE SPEED or CHANGE THE DIRECTION of the force.

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14 Bikes also give you a LOW mechanical advantage. Can you explain why this is a good thing?? What is the trade-off? A bicycle has a M.A. less than one, but you gain the advantage of SPEED by putting in more force than the machine. Mechanical Advantage Formula: MA = Output Force / Input Force WHAT IS THE MECHANICAL ADVANTAGE? In this example, the branch lever has exerted a force that is FIVE TIMES greater than the force you exerted on the branch itself. We therefore say that the branch has a mechanical advantage of 5.

15 Speed Ratio When we look at how a PULLEY can help us create a mechanical advantage, we are measuring the SPEED RATIO. By using a pulley, we gain a mechanical advantage (machine works for us) and a SPEED advantage (faster to lift). SPEED RATIO: The measure of how the speed of an object being lifted is affected by the machine. Input Distance = distance you move Output Distance = distance the load moves Speed Ratio Formula: SR = Input Distance / Output Distance FRICTION AND EFFICIENCY FRICTION is.. a force that oppose motion. It is caused by the roughness of materials as they slide past or over one another. Even surfaces which may seem smooth to us do have a slight amount of "roughness". In order for machines to work properly, the force of FRICTION needs to be overcome. Think of when you move a box up a ramp... where is the friction? Friction affects the MECHANICAL ADVANTAGE of a mechanical device. This is because in a machine, there is always some form of friction between moving parts. Friction is also given off as a form of HEAT.

16 Machines cannot be 100% efficient in real situations due to energy lost as friction / heat. EFFICIENCY is the measurement of how well a machine or device uses energy. Any machine loses some energy as it operates. Usually this energy is lost as heat due to friction. On a bike, you could add lubricant to the chain. In a car, you can make sure the tires are full or air. BOTH REDUCE FRICTION AND INCREASE EFFICIENCY. 2.2 The Science of Work In the scientific sense, work is done when any FORCE acts upon an object to make the object MOVE. MOVEMENT must occur before you can say that work has been / is being done. CALCULATING WORK: Work = Force (N) x Distance (m) where F is the force that you exert and distance is the distance the object moves.

17 2.3 The Big Movers - Hydraulics Most machines that move very large, very heavy objects use a HYDRAULIC system that applies force to levers, gears or pulleys. It is able to INCREASE the MECHANICAL ADVANTAGE of the machine. Modern CONSTRUCTION projects use hydraulic equipment because the work can be done QUICKER and SAFER. There are many practical applications of hydraulic systems that perform tasks, which makes work much easier. A Piston Creates Pressure In hydraulic systems, the pressure is created using a piston. Pistons can be different sizes and hydraulic devices use pistons that are different sizes attached to each other with a flexible pipe. The Input piston is used to apply force to the fluid, which creates pressure in the fluid. The fluid transfers this pressure to the output piston. This pressure exerts a force on the output piston and the result is a mechanical advantage that makes the hydraulic system very useful.

18 3.1 Evaluating Mechanical Devices Mechanical devices have evolved over time because of science and the development of new technologies. We use a set of CRITERIA to evaluate how well and EFFICIENTLY a machine operates, as well as many other criteria. Scientists, engineers, and other inventors want to develop devices that are efficient and effective. Both FUNCTION and DESIGN are considered when building a device. FUNCTION: what the device is supposed to do DESIGN: the form of the device that makes it usable Function and design play a role in evaluating, because developers need to know the why and how in a device they are building. Using Criteria To Evaluate A Device When a device has broken down or become ineffective in performing its function, making decisions as to what new device will replace the broken device have to be made with specific criteria in mind. The list of criteria you decide on will determine how well the replacement will meet your needs. The criteria you use might include:

19 Use Purpose Cost Aesthetics (how it looks) Workmanship (how well it s made) Reputation (company, make, etc) Function and Design Scientists, engineers and inventors want to develop mechanical devices that work the best for the work they are designed to do. The function is the purpose and the design is the form. The design should suit the function. Evaluation For Development Another reason for evaluating a device is to determine how it can be improved. The environment can have an impact on the design of a device as well. The development of mountain terrain bicycles came as a result of how the bicycle would best function in the rough terrain it would be used in. Considering The Environment The effect of a device on the environment should also be considered in evaluating it. The negative impact on the environment should not outweigh the usefulness or effectiveness of the device. 3.2 Technology Develops Through Change New materials and technology, human and environmental needs all contribute to the development of changes to current devices. Some advances in science resulted in new technology, such as electricity. As more people studied and learned more about electricity, new technologies arose.

20 Advances In Science Result In New Technology Charles Coulomb first identified electric charges in the 1700 s, but it took almost 100 years to make electricity widely available to major Canadian cities, and it took until the 1940 s to make it available to most communities in Canada. As scientists and engineers learned more about this new energy source, they found ways to use it in new technologies, such as the light bulb and the electron microscope. From Particles To Trains Another example of technology from science is the MAGLEV Train. These are high-speed trains that have no wheels and traditional tracks, but instead use the power of large magnets to propel the train to incredibly fast speeds km/hr or more! The technology for the MAGLEV resulted from physics experiments using particle accelerators (huge machines used to break apart atoms and other particles of matter) which use large amounts of electricity to create powerful; magnetic and electric fields.

21 Changes In Society Result In New Technology New technology can also result from changes to human society. Robots were originally popularized in movies and comic books. The word robot comes from the Czech word robotnik, meaning workers, or slaves. They were thought to be human-like machines that could do the work of humans. It was originally used in a play where millions were manufactured to work as slaves in factories. Most robots today don t really appear to be human-like, but they do the work of many humans, mostly in industry. The first practical robots were developed in the 1960 s. Robots today weld car bodies together, diffuse bombs, perform surgery, help the handicapped and even explore other planets. Changing Society Changing Technology The drive to develop more effective and efficient robots came from the need to replace humans in the workplace. This was because humans were demanding more money for less hours of work and production costs were soaring. Industry decided to replace humans with robots and most of these were just smart arms. Changes In The Environment Result In New Technology Since the early 1960 s the environment has impacted technological development because people wanted to repair the negative impacts they had made on the environment. New technologies (like recycling) were needed to prevent more damage. Processing materials over and over or making them biodegradable would address some of the issues. Other technologies (like oil skimmers) would help make environmental clean-up more effective and prevent further damage.

22 Mechanical Systems Study Guide 1. What is the difference between a simple machine and a complex machine? 2. Identify the 6 simple machines and describe an advantage of using each one. 3. What type of simple machine is in the following examples: a. Bottle opener b. Your jaw c. Shovel d. Hammer e. Roller blades f. Screwdriver g. Diving board h. Wheel barrow i. Spiral staircase 4. Draw and label the three classes of levers. 5. Describe the effects of simple machines (how they make work easier for us). 6. What is the difference between a system and a subsystem in a complex machine? 7. Identify five subsystems in a bicycle. 8. Define the following: a. Gear b. Linkage c. Transmission 9. What is the difference between a multiplying gear and a reducing gear? 10. Write the definition and formula s for the following: a. Mechanical advantage b. Speed ratio c. Efficiency 11. What does it mean if the mechanical advantage of a system is greater than one? Less than one? 12. Define friction and describe how it affects the mechanical advantage and/or efficiency of a machine. 13. A sailor uses a force of 600 N to pull on a pulley system to raise the sails on a boat. The maximum weight of sails that the sailor can raise with this system is 2400 N. What is the mechanical advantage of the pulley system? 14. What is the difference between force and work? 15. What is the formula for work? 16. What unit is used when you calculate work? 17. What is the work being done when a person pushes with 75 N of force for 3.5 meters? 18. What is the distance that a weight travels if you are pulling on a pulley with 80 N of force and are putting in 440 J?