What is a machine? What are they for? Why do we need them? What are some examples?
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Machines help us work!
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Machines help us to complete work. Their purpose is to make the completion of a job easier to do. But what does work mean in a scientific context?
What is work?
In s cience, the word work has a different meaning than one you ma y be familiar with. l The s cientific definiti on of work is : using a force to move a n object a dista nce (when both the force and the motion of the object a re in the same di rection.) l Lets look a t some examples . l
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Which is work? l
According to the scientific definition, what is work and what is not? l
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A teacher lecturing to his class A mouse pushing a piece of cheese with its nose across the floor
Which is work? l l l l l
A scientist delivers a speech to an audience of his peers. A body builder lifts 100 kilos above his head. A mother carries her baby from room to room. A father pushes a baby in a carriage. A woman carries a 20 kg grocery bag to her car?
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What are simple machines? l
Ancient people invented simple machines that would help them overcome resistive forces and allow them to do the desired work against those forces. l
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But what are these simple machines? There are six types.
Six Types of Machines:1 - 3 Inclined Plane
Wedge
Lever
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Six Types of Machines:4 - 6 Wheel & Axle
Screw
Pulley
The “Seventh” Simple machine: Gears l
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Gears are sometimes considered the 7 th simple machine. However if we examine gears closely we can see that it incorporates : l l
A wheel and axle Levers
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Compound Machines A compound ma chine consists of two or more simple machines put together. l In fact, mos t machines a re compound ma chines. l Compound ma chines can do more diffi cult jobs than simple ma chines alone l Some exa mples are a pai r of s cissors , a bicycle and a wheelba rrow. l
If we look at the wheelbarrow we can identify the different machines involved.
Activity: What simple machines are in a bike? Screws are used to hold the pieces together!
The gear shifts and brake handles are levers.
The peda ls are attached to a lever that turns a pulley
The wheel of a bicycle is a wheel and axle
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Load, Effort and Mechanical Advantage
Load and Effort Load + Effort
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Effort
The load is the object that is moved. The effort is the force that is used to do the work. You can use a simple ma chine to move a large load wi th a smalle r effort than you would need if you did not ha ve a ma chine to help you. This is called gaining a mechanical advantage.
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Mechanical Advantage l
Input Force
l Output Force
It is useful to think about a machine in terms of the input force (the force you apply) and the output force (force which is applied to the task). When a machine takes a small input force and increases the magnitude of the output force, a mechanical advantage has been produced.
Simple Machines - Levers
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Levers A le ver is a ri gid bar that rota tes a round a fi xed or balancing point. l The balancing point is called the Fulcrum. l A le ver uses a force (or effort) to move a load. l There a re 3 types or classes of le ver Depending on the loca tion of the load, the effort and the ful crum l
Example: The See-Saw A see-saw is an example of a class 1 lever!
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Three classes of lever
Class 1 - Lever l
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One example of a class 1 lever would be using a screwdriver to open a can of paint. In this case the screwdriver is the lever Without the screwdriver it would be very difficult to open the can of paint.
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Class 2 - Lever l
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In class 2 levers the fulcrum is at one end of the lever. An example would be lifting a wheelbarrow: l l l l
Lever: Handles Load: The wheel barrow Effort: Person lifting Fulcrum: Axle
Class 3 - Lever l
A class 3 lever is one where: l l l
Tweezers
The ful crum is at one end of the le ver The load is a t the other of the le ver.. The effort is in the mi ddle of the le ver.
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can find at home is when you use tweezers or tongs to pick something up.
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Simple Machines – Wheel and Axle
Wheel and Axles l
A wheel and axle is a simple machine that is made up of : l
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A small central cylinder (Axle). Joined to a larger cylinder (The Wheel)
Wheel and Axles allow us to move a heavy lead much easier.
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Simple Machines – Inclined plane Ramps l Wedges l Screws l
Inclined Plane l
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An example of an inclined plane is a wheelchair ramp, car ramps, roads and even staircases
An inclined plane is a flat surface that is at an angle to the load. This type of machine has no moving part. An incline plane makes it easier to move a load to a greater height.
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Wedge l l
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An example of a wedge is an axe. An axe has two inclined planes which help to do work. When using an axe the downward force is to redirected into horizontal force.
Screw A s crew is reall y an inclined plane wra pped a round a cylinder wi th a wedge a t the tip. l Think of a typical s crew. l
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The wedge is the pointed end. The inclined plane is the thread that wraps around the screw
Screws a re used in many different pla ces to hold things together.
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Simple Machines - Pulleys
What is a Pulley? l
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Pulleys are extremely useful for lifting objects. Most machines used for lifting, such as cranes, have sets of pulleys that magnify the effort.
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Examples of Pulleys
Old Wells
Cran e Pull eys
Flag pol es
Fixed Pulley l
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An example of a fixed pulley is the type you find in a flag pole. A pulley allows a person to stand on the ground and raise the flag. Without a pulley a person would have to climb the pole to raise the flag!
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Moving Pulleys – “Block and Tackle” l
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A moving pulley is also called a “block and tackle”. A moving pulley is actually a double pulley. l l
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One fixed pulley attached to a support. A second pulley attached to the load.
In this diagram the load is an engine from a car.
Pulley Problem:
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A system of four pulley wheels are set up as shown in the diagram above. The driver pulley rotates in an anticlockwise direction. In what direction does the output pulley wheel revolve ?
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Answer: Pulleys in motion Notice how the pulleys working together may rotate in different directions
Science Fact: Archimedes and Pulleys l l l
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Archimedes (287 – 212 BC) Invented the multiple pulley system. Boasted “ Give me a place to stand on, and I shall move the whole Earth” The King challenged Archimedes to prove it.
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Archimedes solution
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Archimedes used a system of pulleys to singlehandedly drag a ship, fully loaded with cargo and passengers, out of the water and onto land.
Simple Machines - Gears
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Gears - “Toothed Wheels” Gea rs are toothed wheels that fit together. l When one gea r turns so does the other. l
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Someti mes gea rs fit di rectl y together (like above) or they work together using a chain or belt.
Gear Trains
A se ries of gea rs fitted directl y together a re called a gear train. l In a gea r train we have a gea r known as the driver and one known as the follower. l
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Driver - is the gear that has the force or motion input. Follower - is the gear that results in the force or motion output.
