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Mechanical Systems- Science 8 FULL UNIT
Transcript of Mechanical Systems- Science 8 FULL UNIT
Levers & Inclined Planes Lever –-is a rigid bar or plank that can rotate around a fixed point Levers are used to reduce the force need to do a particular task.
You can move a very large load, but you must move a greater distance than the load moves. What is Work? work is done when a force acts on an object to make that object move. In order to say that work is being done, there must be movement. The formula looks like this: W = F x d Force is measured in Newtons and distance is measured in meters. The resulting work unit is called a joule named after the English scientist James Joule. Work and Machines There are different types of simple machines that can help us do work. Work input is the work needed to use, or operate the machine Work output is the work done by the machine. youtube- how levers work 1:42 youtube- Eureka! episode 11 - inclined plane 5 mins youtube- Eureka! episode 12 - the Lever 5 mins Work and Friction Friction is the reason that work input does not equal work output in real situations. Friction affects the machine’s efficiency. Mechanical Advantage Mechanical Advantage is the comparison of the force produced by a machine to the force applied to the machine. the size of the load vs the size of the force needed to move the load MA = Load Force
Effort Force youtube- Eureka! episode 13 - MA & Friction 5 mins Inclined plane Or ramp, makes it easier to move a load higher than it is, but, it has to be moved over a much longer distance. (examples: loading ramp, wheelchair access ramp) Question!
What is 'ergonomics' Topic 2-
The Wheel and Axle, Gears and Pulleys youtube- Eureka! Episode 14 The Screw & Wheel 5mins youtube- Eureka! Episode 15 The Pulley 5mins A Lever That keeps on Lifting A winch consists of a small cylinder that has a crank or handle. The axle of the winch acts like the fulcrum, the handle is the effort arm. Because the handle is longer than the radius of the wheel, the effort force is smaller than the load – making it act like a small lever over and over again. The Wheel and Axle combination of two wheels of different diameters that turn together A longer motion on the wheel produces a more powerful motion on the axle, thus giving it a mechanical advantage (steering wheel in a car). Several simple machines all working together in a system are called complex machines. A system is a group of parts that work together to perform a 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. How many simple Machines? Linkages In the bicycle, the chain is the linkage. The linkage is the part of the subsystem that transfers your energy from the pedals to the back wheel. – one that drives the motion and the other will follow in the same direction. Chains or belts form a direct link between two wheels Transmissions Machines that are more complex than a bicycle move much larger loads. A transmission contains a number of different gears. READ PAGE 285 READ page 286 Gears They consist of a pair of wheels
that have teeth that interlink.
Gears are essential components of most mechanical systems Read page 287 When they rotate together, one gearwheel transfers turning motion
and force to the other. what happens here? Gears transfer energy in a mechanical system. Gear wheels – which are wheels with precisely
manufactured, identical teeth around its edge The gear that supplies the energy is called the driving gear. The gear to which the force is directed is called the driven gear. It can be calculated by dividing the number of driver gear teeth by the number of follower gear teeth. speed ratio.
One or more combinations of wheels and ropes can be
fixed in place or moveable. Depending on the number of pulleys used, A Pulley consists of a wire, rope, or cable
moving on a grooved wheel. single fixed pulley! single movable pulley! Pulleys help you lift larger loads. OMG! Supercharging Pulleys A very complex combination of pulleys, including fixed and movable is called a.... block and tackle a block and tackle can have a large mechanical advantage. reading page 289 292-293 in textbook for more information Topic 3-
Energy, Friction, and Efficiency
Work and Energy
Machines help people do things that they normally couldn’t do on their own
Work is a transfer of energy. what type of energy is moving the windmills?
what type of energy is being created? Examples of energy:
Thermal In the example of the bicycle – your energy (chemical energy from your food) is transferred to the pedals giving them kinetic energy, or energy of motion.
Stored Energy Stored energy is called potential energy. Much of the energy for machines is stored as chemical potential energy.
Gravitational potential energy is transferred to kinetic energy in machines in a dam to generate electrical energy. Energy cannot be created nor destroyed – It is only transformed or transferred! SUPER IMPORTANT! let's make some energy transmittions KINETIC ENERGY ELECTRICAL ENERGY ELECTRICAL ENERGY THERMAL ENERGY THERMAL ENERGY ELECTRICAL ENERGY
No Machine is 100% Efficient
An ideal machine would transfer all the energy it received to a load or to another machine. However there are no ideal machines. Real machines lose energy. The work output of a real
machine is always less than the work input. read pages 296 read pages 298-299 The reason that machines are never 100% efficient is because of the energy that is lost by a machine to friction.
The higher the efficiency, the better the machine is transferring energy. video- 2:40 video 1:34 Eureka! Episode 8 - Work- 5mins Eureka! Episode 9 - Kinetic Energy Eureka! Episode 10 - Potential Energy
Since some of the effort force put into a machine is used to overcome the frictional force of the
will help to reduce friction and increase efficiency. reducing the surface area interaction where
parts rub together and good maintenance of the machine
Useful Friction There are reasons why we need friction in a machine for it to perform properly. Slipping and sliding would occur and proper gripping would be impossible without friction. There are many places where friction is useful, including: Bicycles tires create friction with the road surface to give you grip Gymnasts use rosin to provide grip on slippery metal surfaces (like rings or bars) Curlers sweep the ice in front of the rock to decrease friction with the ice surface A speedy review 1. The load in a wheelbarrow would be easier to lift if the handles on the wheelbarrow were shorter.
2. A teeter-totter is a Class 1 lever.
3. Every time you move one of your fingers, arms, or toes, you are using a lever.
4. When you slide a box up a ramp onto a stage, you do less work than if you were to lift the box onto the stage.
5. If you lift a box weighing 100 N a height of 5 meter into the back of a van, you have
done 500 J of work.
6. If, when using a lever, you exert an effort force of 5 N to lift a load of 10 N, your lever has a mechanical advantage of 2.
7. Friction, noise, and heat have no effect on the efficiency of machines.
B) False 8. In what unit is work measured?
D) kilograms 9. The Canadarm functions much like a human arm. Which type of lever does it use most?
A) Class 1 lever
B) Class 2 lever
C) Class 3 lever
D) the mobile servicing system
10. Two simple machines that are part of a bicycle are _______________________ .
A) a gear and a wheel and axle
B) an inclined plane and a lever
C) an inclined plane and a wedge
D) a screw and an inclined plane
10 questions! Pressure is a measure of the amount of force applied to a given area. The unit of measurement for pressure is a pascal (Pa), named after Blaise Pascal who did important research on fluids. Blaise Pascal (1623-1662)
discovered that … From Pascal’s law, we know that the pressure the small piston creates is the same everywhere in the fluid. To increase the force on the output piston , the input piston must move through a greater distance. Topic 5 – Hydraulics and Pneumatics The air usually passes through the pneumatic device under high pressure and then escapes outside the device. The high pressure air is used to do the work Life depends on a pneumatic system in your body – namely the respiratory system. Topic 6 –
Groups of parts that perform specific functions, in a complex machine, are called subsystems.
Each subsystem in a complex machine contains a simple machine and usually has just one function. The assembly of the 3 levers swings around on a gear-like part called the slew ring. Topic 8 –
People & Machines Improving machines brought lots of positives, but there were also some negative side effects (like pollution). People flocked to the cities to get work in the factories – the shift from rural living to urban dwellers began. Today alternative fuel sources (solar-powered, electricity, hybrids, propane and hydrogen fuel cells) are being tested and are utilized to a very small extent. Scientists often have to ask
themselves difficult questions, weighing the positive and negative effects of the technology.
Designing for Comfort
Many of the principles of design rely on the physics principles of Force, Area and Pressure Ergonomics is: The Science of Comfort
The heart is actually two pumps that circulate your blood throughout the body. Four automatic valves are used to help circulate the blood. Topic 4- Force, Pressure and Area Sandblasting an old building made of stone or brick can make it look almost like new. Sandblasting is also used to roughen surfaces to improve traction, by increasing friction. Medical engineers have developed a type of cast filled with pressurized air, which makes it fit snugly and securely. Calculating the input force and the output force will give you the Mechanical advantage of the system.
MA = Output force / Input force EACH Device is using pressure Calculating Pressure
1 Pascal is equal to the force of 1 Newton over an area of 1 m
p is pressure
F is Force and
A is Area
1 Kilopascal is equal to 1000 pascals 2 Safety equipment is need in many situations in order to protect our body from injury or accident. He was the first to notice that the shape of the container had no effect on the pressure at any given depth as illustrated here. This is known as Pascal’s Law and it makes hydraulic (liquid) and pneumatic (air) systems possible. "Pressure applied to an enclosed fluid is transmitted undiminished in all directions throughout the fluid and perpendicular to the walls of the container." Most of the safety equipment is designed to spread the force over a larger area. Equipped Against
Pascal’s Law A common application of Pascal’s law is the hydraulic lift.
It is a mechanical system that raises heavy objects, using a fluid under pressure in a closed system (self-contained collection of parts).
(MA) MA Load
Effort EXAMPLE 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. 3 2 1 The mechanical advantage in a hydraulic system comes from the fluid pressure in the system.
Mechanical advantages in hydraulic systems are usually quite high, showing how useful they are.
The reason for the large mechanical advantage in a hydraulic system is the ability of the fluid to transmit pressure equally. It allows you to use a small force on the small piston to produce a larger force on the large piston.
p = F / A
By solving this ratio you will find that the forces created within a hydraulic system provides very large mechanical advantages - making them useful in many applications.
Larger Force –
Greater Distance To Move
Mechanical advantage in hydraulic systems has a cost.
That cost is the increased distance the smaller force must go through to make the large force move a small distance.
Amusement park rides make extensive use of hydraulic systems Hydraulic systems use the force of a liquid in a confined space.
Hydraulic systems apply two essential characteristic of fluids – their incompressibility and their ability to transmit pressure.
Pneumatic systems do not seal the gas (usually air) in the same way as hydraulic systems seal in the fluid it uses.
Pneumatics at Work
Examples of pneumatic devices that are used to do work:
The jackhammer The loud noise of the jackhammer is the compressed air at work. Bursts of air, under very high pressure drive the ‘chuck’ in and out of the jackhammer at high speeds, which pounds the concrete – breaking it up into small rocks or fragments.
Staple guns and pneumatic nailers use pulses of air pressure to drive staples or nails into solid objects.
Sandblasters do exactly what the name implies.
High pressure air blasts tiny sand particles out of a nozzle to remove dirt and paint from stone or rock.
Riding on Air
Hovercrafts are used by the Canadian Coast Guard in search and rescue missions.
They are also used commercially, to transport people, cars and equipment over long distances on land or water.
The hovercraft has a pump that draws air from outside and pumps it out through small holes in the bottom of the hovercraft.
Propellers on the back of the craft drive the hovercraft forward, and rudders are used to steer it. A skirt around the bottom holds enough air to support the weight of the craft above the water or land.
Most machines that move very large, very heavy objects use a hydraulic system that applies force to levers, gears or pulleys. Hydraulics at Work
Modern construction projects use hydraulic equipment because the work can be done quicker and safer. Examples of hydraulic devices that are used to do work:
The Earthmovers The cherrypicker is an example of a hydraulic device that is used to do raise workers to high places to repair or do work at heights that normally could not be reached safely. Jaws of Life The various parts of an airplane wing are raised and lowered hydraulically.
Hydraulics are also responsible for tail adjustments to enable the pilot to turn the plane in the air. Hydraulics in Flight
Wheels are raised and lowered using a hydraulic system as well. There are different hydraulic systems in different aircraft, but all the systems work together in much the same way to provide reliable and safe adjustments when the plane is taking off, airborne and landing. Dentist Drills too! it's a good thing that it works on air...
if it was a hydraulics system, then the drill would keep drilling past the tooth. The heart (your hydraulic device) pumps the blood (fluid) around your body carrying food and nutrients to all cells in your body. Breathing depends on changes in air pressure. You breathe in and out about 12 times a minute, exchanging about 500ml of air each time. Hydraulics and Pneumatics in Your Body
Your body also depends on a complex hydraulic system – the circulatory system.
& Valves and Pumps
A valve is used to control the flow of a fluid.
It is a moveable part that controls the flow by opening or closing.
Many pumps use automatic valves controlled by pressure to move fluids in specific directions.
Pressure on one side opens the valve and closes when the pressure on the other side is greater.
Between heartbeats the pressure changes allowing the valves to open and close when they are supposed to. As time passed, people expected more and more difficult tasks to be completed by machines.
Machines became more complex.
Several simple machines all working together in a system are called complex machines.
A system is a group of parts that work together to perform a function.
The different subsystems in a mechanical device can produce a force advantage, such as the disc brakes in a car.
The brake fluid transfers the pressure from the brake pedal to the brake pads and the disc, which produces enough force to stop the car.
Another example of a highly efficient combination of levers and hydraulics is the backhoe.
The backhoe is a combination of 3 levers, called the boom (class 3 lever), the dipper (class 1 lever) and the bucket (class 1 lever).
Topic 7 –
Throughout History Past to Present examples: Thomas Savery developed the first practical steam engine in 1699. He heated water to make steam and then used it to move a piston.
When the piston moved, it caused an attached rod (which was connected to a crankshaft) to move as well, making the engine work. Putting Steam To Work
Water Technologies Rail Technologies Steam Engines:
Paddle wheeled steam boat:
Combustion Engines: Please define how the following machine improvements work Can you now develop your own timeline on how machines have transformed over time, still trying to accomplish the same goal? Science and technology have given us many different amazing machines that have made our daily tasks easier.
The automobile caught on very quickly, but the ideal machine soon demonstrated its greatest flaw.
Pollution of the environment was a result of more and more fossil fuels being burned, in larger vehicles.
http://goodcomics.comicbookresources.com/2009/03/19/comic-book-legends-revealed-199/ Collected websites used in this Prezi This list is being populated Water-driven spinning machines were used in 1769 and could finish the work of 12 workers.
James Watt’s efficient steam engine and Henry Cort’s use of coal for fuel (instead of wood) to make iron started the Industrial Revolution.
Mass production industries began and soon small towns became industrialized cities, leading to social change.
The invention of the steam engine transformed society. Simple machinery replaced hand labor since 1700.
The Industrial Revolution
Which Came First?
Did technology change society or has society changed our technology?
The automobile uses cheap fuel and therefore more vehicles are being used.
With cities so large, people need a vehicle to travel from place to place. OR, is the convenience of having a vehicle just societies’ reason to have larger cities?
Because of the impact of scientific knowledge on society preferences for styles and sizes of vehicles changed.
Larger vehicles polluted more and cost more to operate, so society wanted more compact fuel efficient vehicles.
Positive Negative Negative When a new technology is being designed or an old technology improved upon the starting point must be the function – what is it that you want the technology to do?
Nuclear power is just one example
clean and efficient power generation nuclear accidents devastate the environment VS The ethical issues must be reviewed and considered in the decision to go ahead. How do inventors use their understanding of scientific concepts to design a new device, or modify an old one?
...and now a Rube Goldberg Machine to celebrate the end of the UNIT!