Floatlakie.weebly.com



1. – Machines are tools that help humans do work.

1. – Simple Machines – Meeting Human Needs

A machine is any mechanical device that helps us do work. Over the years these machines have become more complex and more efficient.

[pic][pic]

[pic]

The earliest machines were very simple. In fact they are referred to as simple machines. The six common simple machines are: the lever, the inclined plane, the pulley, the screw, the wedge and the wheel and axle.

[pic][pic][pic][pic][pic][pic]

Lever

The leaver consists of a rigid bar that pivots or rotates around a fixed point called a fulcrum. Arranging a lever in specific ways allows you to lift a load with less force. There are three classes or types of levers.

[pic]

____________________________________________________________________________________________________________

____________________________________________________________________________________________________________

____________________________________________________________________________________________________________

Inclined Plane

The inclined plane is simply a ramp that is set at an angle. It allows you to move a load from one level to a higher level with less effort. It also allows a load to be lowered at a safer rate. Instead of a load being dropped vertically it can be let down gradually.

[pic] [pic] [pic]

Wedge

A wedge is an object that is narrow at one end and wider at the other end. It is two inclined planes attached. A wedge is forced into an object or between two objects to force them apart. A wedge makes it easier to move things apart.

[pic][pic][pic][pic]

A Screw

A screw is like an inclined plane (or a wedge) wrapped around a cylinder. The screw can convert force into a forward motion, like the Archimedes’s screw below. It is most used to fasten objects together.

[pic][pic]

Pulley

A pulley consists of a rope / string moving on a grooved wheel. You can use one pulley alone or use more than one pulley together to make it possible to lift a load with even less effort.

[pic][pic][pic]

Wheel and Axle

This consists of a larger wheel connected to a smaller axle. When you turn the wheel to make the axle turn you can move loads with much less effort. If you move the axle to move the wheel you can cause a speed advantage.

[pic] [pic] [pic] [pic]

Machines Help Us Do Work in Two Ways

Machines will either give us a force advantage or a speed advantage.

Force Advantage (mechanical advantage) – It takes less force to complete a task. This allows you to move an otherwise impossible object. However, we end up traveling a greater distance during the process.

Speed Advantage – We can speed up an action. This allows us to make something move faster than we would be able to otherwise. However, it may take more effort to complete the task.

Lifting Things With Pulleys

| | |Force Required to Lift the Weight (N) |

| |Weight (N) |1 Pulley |2 Pulleys |3 Pulleys |

|1 kg Weight | | | | |

| | | | | |

| | | | | |

How much force advantage do you gain from one pulley? _______________

How much force advantage do you gain from two pulleys? _______________

How much force advantage do you gain from three pulleys? _______________

Say you had a car that weighed 4000 pounds. That is about 1800 kg. How many pulleys would you need to lift the car? _______________

Do you think the size of the pulley makes a difference? __________ How? __________________________________________________________________________________________________________________________________________

Check and Reflect – Mechanical Systems – Section 1 #1

1. What is a machine? ______________________________________________

2. What are the 6 simple machines? ____________________________________

__________________________________________________________________________________________________________________________________

3. Use a diagram to describe the three classes of levers. Give one example for each class.

4. What two advantages can we gain by using a machine? _____________________________________________________________________________________________________________________________________________________________________________________________

5. How can you make a pulley work even better for you?

______________________________________________________________________________________________________________________________

_______________________________________________________________

6. How are an inclined plane and a wedge similar? ______________________________________________________________________________________________________________________________

Lever Investigation

Your group needs to figure out how to arrange the load, effort and fulcrum in order to lift the load with the least amount of effort possible for each class of lever. Once you have figured it out sketch your lever on this sheet and write down how much effort it has taken to lift the 1kg load. Good Luck.

1st Class Lever Minimum Effort _________________

2nd Class Lever Minimum Effort _________________

3rd Class Lever Minimum Effort _________________

1.2 – The Complex Machine – A Mechanical Team

Complex Machines are devices that are made up of several simple machines, which all work together to perform a function. A complex machine is also referred to as a system.

An example of a system is a bicycle. A subsystem consists of a group of parts that perform a specific function. Within a bicycle are subsystems that control braking, steering or accelerating. Subsystems usually contain one or a few simple machines. Identify some subsystems on the bike below.

[pic]

In complex machines that produce motion some of the subsystems are responsible for the transfer of energy / force. These subsystems are called linkages and transmissions. Often they involve gears.

Linkages

Movement is accomplished with a complex machine when energy from some source is transferred to the object being moved. In a bicycle the wheels are the object being moved. The linkage is the part of the bike that transfers your energy from the pedals to the back wheel. What is the linkage on a bike? __________________________________

Transmissions

With complex machines that are more complex than a bicycle and move larger loads than just one person we use a special type of linkage called a transmission. These machines use gears that are designed to transfer much larger forces.

Gears

Gears can alter movement in many ways. When gears are connected by a chain the transfer movement in the same direction

[pic]

When gears mesh with one another the movement is transferred in the opposite direction

[pic]

The driving gear is the gear that is applying a force. The driven gear is the gear that has the force applied to it.

When the smaller gear is the driving gear it decreases the speed of rotation. This set of gears would be referred to as reducing gears because the speed of rotation has been decreased. In the diagram below how many times would the smaller driving gear have to go around in order for the larger driven gear to go around once? _______

[pic]

When the larger gear is the driving gear it increases the speed of rotation. This set of gears would be referred to as multiplying gears because the speed of rotation has been increased.

If we were climbing a hill with a mountain bike what size gear would we want on the front and what size would we want on the back to make our work easier? ________________________________________________________

If we were pedalling down a hill with a mountain bike what size gear would we want on the front and what size would we want on the back to go the fastest we could go? ________________________________________________________

Gear Ratios on a Bike

Problem - Does a 21 speed bike actually have 21 speeds?

Hypothesis - ________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Variables

Manipulated - _____________________________________________

Responding - ______________________________________________

Controlled - _______________________________________________

- _______________________________________________

- _______________________________________________

Procedures

1. _______________________________________________________

2. _______________________________________________________

3. _______________________________________________________

4. _______________________________________________________

5. _______________________________________________________

6. _______________________________________________________

7. _______________________________________________________

Materials - ________________________________________________

Observations

|Gear Arrangement 1 |Front - |Back - |

|Gear Ratio |Number of Rotations |Number of Teeth |

| | | |

| | | |

| | | |

|Gear Arrangement 2 |Front - |Back - |

|Gear Ratio |Number of Rotations |Number of Teeth |

| | | |

| | | |

|Gear Arrangement 3 |Front - |Back - |

|Gear Ratio |Number of Rotations |Number of Teeth |

| | | |

| | | |

Conclusion

1. Restate the hypothesis _______________________________________

_________________________________________________________

2. Is your hypothesis right? _____________________________________

3. How do you know? _________________________________________

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Check and Reflect – Section 1 #2

1. On each picture label the effort, fulcrum and load. Then identify which class of lever it is.

[pic] [pic] [pic]

2. What should you do to a class two lever in order to lift the load with the least amount of effort? ________________________________________________________

________________________________________________________

3. In complex machines the subsystems that are responsible for transferring energy to produce movement are called ________________ or __________________

4. What is a driving gear? ____________________________________

_______________________________________________________

7. What is a driven gear? _______________________________________________________

________________________________________________________

8. When the smallest gear in a gear train is the driving gear what is it called? ______________________. How will this affect the speed of rotation? _____________________________________.

9. If you are climbing a hill what size sprocket would you need on the front and the back? _______________________________________.

Mechanical Systems – Section 1 Assignment

Do all questions in your homework book.

1. Sketch a 3rd class lever in your book and label the effort, load and fulcrum. Then list two examples of a 3rd class lever. /3

2. What would you have to do to a 1st class lever to lift the load with the least amount of effort? /1

3. What advantage do we gain when we use a simple machine? /1

4. What is the difference between a linkage and a transmission? /1

5. If you are trying to gain a force advantage using gears, what size should your driving gear be compared to the driven gear? /1

6. What is a gear ratio? /1

7. What is the linkage on a bike and what does it do? /2

8. What is a multiplying gear? What is a reducing gear? /2

2. An understanding of mechanical advantage and work helps in determining the efficiency of machines.

2.2 – The Science of Work

The scientific definition of work is applying a force to an object causing it to move in the general direction of the force. We can calculate how much work is being done with the following formula:

W = F x d

• W is the amount of work being done. The unit used to measure work is Joules (J), named after the English scientist James Joule.

• F is the amount of force being used to move the load. The unit used to measure force is Newtons (N), named after the English physicist and mathematician Sir Isaac Newton.

• d is the distance the load is moved. The distance must be in meters (m).

If you were to lift your chair up on your desk, how much work would you do? If the distance to the top of your desk was 0.4 m and the force needed to lift the chair was 50 N the calculation would look like this:

W = F x d

= 50 N x 0.4 m

= 20 Nm

= 20 J * 20 Nm = 20 J

So lifting your chair onto your desk did 20 Joules of work.

Calculating Work with Simple Machines

Incline Plane

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Pulley

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Wheel and Axle

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Lever

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

1. – Machines Make Work Easier

Mechanical Advantage

A machine makes work easier by decreasing the amount of effort you need to exert in order to move a load. This is called a mechanical advantage. Really what the machine is doing is multiplying your effort so it can lift the load easier. The input force is the force that we apply to the machine. The output force is the force that is exerted by the load. We can calculate Mechanical Advantage with the following formula:

MA = Output

Input

• MA is the mechanical advantage. There are no units for this measure.

• Output is the output force of the load. Because it is a force being measured the units are Newtons (N).

• Input is the input force or the force exerted on the machine. The units for this are also Newtons (N).

If we were lifting a load with a two wheel pulley and the force the load exerted was 200N and we exerted a force of 100 N on the pulley in order to lift the load the calculations would look like this:

MA = Output

Input

= 200 N

100 N

= 2 * remember there are no units for MA

So lifting a 200 N load with a two wheel pulley gives you a mechanical advantage of 2.

Calculating Mechanical Advantage with Simple Machines

Incline Plane

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Pulley

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Wheel and Axle

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Lever

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Speed Ratio

Speed measures the distance a load travels in a given amount of time. Speed Ratio is a measure of how the speed of the object is affected by a machine. The input distance is how far effort is exerted on the machine. The output distance is how far the load moves. Speed Ratio is calculated by dividing the input distance by the output distance.

SR = Input Distance

Output Distance

• SR is the speed ratio. There are no units for this measure.

• Input distance is how far effort is exerted on the machine. This is measured in meters (m).

• Output distance is how far the load moves. This is also measured in meters (m).

A load is being lifted using a 1st class lever. If the effort is exerted on the lever was a distance of 3 m and the load moves1 m then the calculation will look like this:

SR = Input Distance

Output Distance

= 3

1

= 3 *remember there are no units

So the speed ratio for moving a load over a distance of 1 meter using a 1st class lever is 3.

Calculating Speed Ratio with Simple Machines

Incline Plane

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Pulley

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Wheel and Axle

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Lever

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Friction

In all cases machines create friction when they move. Wherever two surfaces are in contact there will be friction. So the efficiency of a machine moving a load will always be less than 100%. Friction creates heat. This heat can over heat the system and cause it to fail. Often special fans and lubricants are used to reduce the amount of heat created by friction.

Efficiency

Efficiency is a measure of how well a machine uses energy. When mechanical devices are used some of the energy (muscle, fuel, electricity, oil) is lost. Usually it is lost as heat. We say it is “lost” because the energy is not being used to move the load. The more energy that is lost the less efficient the machine is. Efficiency is expressed as a %. So a machine that is 40% efficient loses more energy than one that is 70% efficient. Efficiency is calculated with the following formula:

E = MA x 100

SR

• E is the efficiency. It is expressed as a %.

• MA is the mechanical advantage.

• SR is the speed ratio.

• After dividing MA by the SR you multiply it all by 100.

So if your MA is 2 and your SR is 3 your calculation would look like this:

E = MA x 100

SR

= 2 x100

3

= 0.6667 x 100

= 66.67%

Calculating Efficiency with Simple Machines

Incline Plane

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Pulley

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Wheel and Axle

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Lever

_______________________

_______________________

_______________________

_______________________

_______________________

_______________________

Check and Reflect – Section 2 #1

1. Is work being done in the following examples? Explain your answers

a. A hiker puts her backpack on. ____________________________

____________________________________________________

b. A gardener pulls on a large weed as hard as he can, but he can’t get it out of the ground._________________________________

____________________________________________________

c. A student memorizes a poem. ____________________________

____________________________________________________

2. What units do you use to measure force? ______________________

3. What units do you use to measure work? ______________________

4. What units should we use for distance when we are calculating work? ___________________________

5. Calculate work for the following examples (show all your work):

a. A 15 N box is lifted 0.5 m

b. A 500 N table is pushed 200 cm up a ramp.

c. A pulley is used to lift a 1000 N piano up 10 m.

Check and Reflect – Section 2 #2

1. What is a mechanical advantage? ____________________________

________________________________________________________________________________________________________________

2. Why is the efficiency of a machine never 100%? ________________

________________________________________________________________________________________________________________

3. What are three sources of energy? ____________________________

________________________________________________________

4. Why is energy considered lost when it is not being used to move the load? ________________________________________________________________________________________________________________________________________________________________________

5. Calculate mechanical advantage, speed ratio and efficiency for the following example. A load is being lifted by a 2 wheel pulley. The input force = 5.2 N, output force = 10 N, input distance = 1 m, output distance = 0.5 m

3. – The Big Movers – Hydraulics

Hydraulic Systems

A hydraulic system uses liquids under pressure to move very heavy loads. Pressure is a measure of the amount of force applied to a given area. Pressure can be calculated by the following formula:

p = F / A

• p is the pressure. The units used to measure pressure is the pascal (Pa) named after the scientist Blaise Pascal. It can also be measured in Newtons per square centimetre (N/cm2).

• F is the force being applied. It is measured in Newtons.

• A is the area the fluid is occupying. It is measured in square centimetres (cm2).

So in a situation where a 20 N force is applied on a 4 cm2 area this is how

you would calculate how much pressure there is:

p = F

A

= 20 N

4cm2

= 5 N/cm2

In Pascal’s research he discovered that pressure applied to an enclosed fluid is transmitted equally in all directions throughout the fluid. This effect is known as Pascal’s Law. That is why these systems have such large mechanical advantages, which means they can lift enormous loads.

[pic]

____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

Check and Reflect Section 2 #3

1. What is a hydraulic system? __________________________________

________________________________________________________________________________________________________________________

2. What is Pascal’s Law? _______________________________________

________________________________________________________________________________________________________________________

3. What units do we use for pressure? ____________ or ______________

4. What would our mechanical advantage be if we were using a hydraulic system to move a load? _________________________________________

5. Calculate pressure for each example. Round each answer to the nearest tenth where necessary.

a) force = 25N area = 6cm2

b) force = 40N area = 9cm2

c) force = 55N area = 12cm2

Mechanical Systems – Study Guide

Know the meaning of the following terms:

machine, simple machine, fulcrum, load, effort, manipulated variable, responding variable, controlled variable, complex machine, system, subsystem, linkage, transmission, gears, driving gear, driven gear, reducing gears, multiplying gears, work, mechanical advantage, input force, output force, speed ratio, input distance, output distance, friction, efficiency, hydraulic system, pressure, Pascal’s law

Be able to explain the following:

• Describe how each of the 6 simple machines work.

• Label each class of lever with a fulcrum, load and effort.

• Describe how you would arrange each class of lever so that it lifted a load with the least amount of effort.

• Explain how machines help us do work.

• Identify some subsystems on a bike.

• Explain the function of a linkage or transmission.

• Identify the linkage on a bike and what it does.

• Describe how a linkage and transmission are different.

• Explain how you could increase the speed of rotation using gears.

• Explain how you could decrease the speed of rotation using gears.

• What size sprockets would you have on the front and back of a bike when climbing a hill? Going as fast as possible?

• What are the units used to measure work, force, distance (when calculating work), mechanical advantage, speed ratio, efficiency and pressure.

• Calculate work, mechanical advantage, speed ratio efficiency and pressure.

• Explain how energy is “lost” when using a mechanical device.

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download