history of machines machines & work. history of machines throughout history, people have learned...
TRANSCRIPT
History of Machines
Machines & Work
History of Machines
Throughout history, people have learned ways to increase force, change the direction of force, and increase the rate of work.
A machine is a device that helps us do these things.
History of Machines
We do not know what the first machine was. It may have been the tree branch that prehistoric people used as a lever to move a huge stone, or the sharp rock used as a scraper (wedge) to skin animal hides.
Later, people discovered the use of logs as rollers. This perhaps encouraged the idea for the invention of the wheel and axle.
History of Machines
An inclined plane, used by ancient civilizations, was simply a sloping surface.
The pulley was a much later invention, as was the screw.
History of Machines
The Industrial Revolution, which began in Great Britain in the 1700’s, was sparked by the invention of the steam engine.
The Industrial Revolution helped bring people into the machine age and vastly increased the availability of many kinds of products.
History of Machines
Machines enable people to do more work in less time.
Many machines are controlled by computers, and many tasks are now performed by robots. Therefore, the present time is often referred to as the “computer age.”
Simple Machines
Machines & Work
Simple Machines
Although a machine produces force and controls the direction of force, it cannot create energy.
A machine can never do more work than the amount of energy put into it; it can only transform one kind of energy into another kind.
For example, an electric food mixer turns electrical energy into mechanical energy.
Simple Machines
Many machines are complex and contain a number of parts that are meant to work together.
No matter how complex they are, however, all machines are forms of six simple machines or combinations of them.
Simple machines help us make better use of our muscles.
Simple Machines
Scientists have identified six simple machines:
1. lever – stiff, rigid bar that pivots on a point (fulcrum) and moves resistance (load or weight)2. inclined plane – a sloping surface3. wedge – two inclined planes placed back to back4. screw – spiral inclined plane5. pulley – freely turning wheel over which a rope or wire can be passed6. wheel and axle – a wheel fastened to a shaft, both of which move around a common point
The Lever
Machines & Work
The Lever
Levers are used frequently in our daily lives to make work easier.
The lever is one of the earliest and simplest of machines.
It consists of a rigid bar and three elements.– The resistance is the weight that the lever moves– The fulcrum is the fixed pivoting point– The effort is the push or pull applied to the lever
The Lever
The Lever
Levers are divided into three classes depending on the position of the effort, resistance, and fulcrum in relation to each other.– First-class lever: fulcrum is located anywhere
between the effort and resistance (load/weight)– Second-class lever: resistance is between the
effort and the fulcrum– Third-class lever: effort is between the
resistance and fulcrum
The Lever
First-class lever: fulcrum is located anywhere between the effort and resistance (load/weight)
Second-class lever: resistance is between the effort and the fulcrum
Third-class lever: effort is between the resistance and fulcrum
The Lever
When the fulcrum is closer to the effort than to the resistance, there is a loss in effort but a gain in speed and distance.
The closer the fulcrum is to the resistance (weight/load), the less effort is needed to lift the resistance.
The position of the fulcrum determines the amount of effort needed to move an object, and the distance and speed at which the object moves.
The Wheel and Axle
Machines & Work
The Wheel and Axle
The wheel and axle is one of the most important inventions in history.
It lifts heavy loads with relatively little effort.
The roller, forerunner to the wheel and axle, may have been one of the earliest inventions to help people do work.
The Wheel and Axle
Several logs placed under a heavy object helped reduce friction so the object was moved with less effort.
But this was a slow, cumbersome process. The logs had to be moved from the ground behind the object to the ground in front of the object before the object itself could be moved.
The discovery that thin sections of a log could be joined rigidly by a pole or log helped people make a more efficient machine – the wheel and axle.
The Wheel and Axle
The wheel and axle is basically a modified lever; the center of the axle serves as a fulcrum.
In wheel and axle machines, the wheel is sometimes replaced with a crank, as in the handle of a pencil sharpener.
The handle can be thought of as the spoke of a wheel. As the handle turns, it makes a circle with greater force. The cutting blades can then sharpen the pencil.
The Inclined Plane, Wedge, and Screw
Machines & Work
The Inclined Plane, Wedge, and Screw
The inclined plane is such a simple machine that people often do not realize it is a machine. It can be any slanted surface used to raise a load from a lower level to a higher level.
Using an inclined plane may make lifting heavy loads easier because less effort is needed, but does not make less work.
The Inclined Plane, Wedge, and Screw
Examples of Inclined Planes
The Inclined Plane, Wedge, and Screw
The wedge is a form of inclined plane which is used to increase force.
A single wedge, having one sloping surface, resembles an inclined plane.
Two inclined planes with a common base form a double wedge.
Wedges can be used to split things apart. If the edges are sharpened, they can be used to cut things.
The Inclined Plane, Wedge, and Screw
Examples of Wedges
The Inclined Plane, Wedge, and Screw
The screw is another form of an inclined plane. It increases force.
A screw has two parts: the body (cylinder) and the thread (the inclined plane wound around the cylinder)
The pitch of a screw is the distance between two consecutive threads.
The Inclined Plane, Wedge, and Screw
Examples of Screws
The Pulley
Machines & Work
The Pulley
A simple pulley is a grooved wheel firmly attached to an axle. A rope passed over the wheel, fits into the groove so it doesn’t slip off. One end of the rope is attached to a bucket or other load. When the other end of the rope is pulled (effort), the load is lifted.
The Pulley
A fixed pulley is a simple pulley fastened to one spot.
It works like a turning first-class lever. The fulcrum is between the effort and the resistance.
The Pulley
A movable pulley is a simple pulley that moves along a rope or wire. It gives a gain in force, but a loss in distance.
It works like a turning second-class lever. The resistance is between the fulcrum and the effort.
The Pulley
A compound pulley, also known as a block and tackle, is a combination of fixed and movable pulleys.
The block and tackle pulley changes direction and gives a gain in force at the same time.
The block and tackle is used to hoist or haul heavy loads.
Compound Machines
Machines & Work
Compound Machines
The many compound machines in our modern world are combinations of one or more simple machines.
These machines help us by producing a gain in distance, force, or speed.
An ax is an example of one of the earliest compound machines. The handle is a lever and the ax-head is a wedge.
Force
Machines & Work
Force
Whenever an object is caused to move, whether from a standstill or while already in motion, a force is required. The force may be a push or pull.
Gravity is a universal force and causes every object to attract every other object.
Gravity is the force that causes a ball to drop to the earth and keeps the moon orbiting the earth.
Force
Magnetic fields are also forces that cause motion. Certain elements that exhibit magnetic properties can become magnetized.
Electric forces are due to the charges of atomic particles.
Static electricity is due to charged particles.
Force
Friction opposes motion and occurs when two substances rub against each other.
The motion of objects is reduced because of friction.
Work and Power
Machines & Work
Work and Power
The principle of a machine is that it makes work easier.
The amount of work a machine produces equals the force used multiplied by the distance the machine lifts or moves an object.
Work = Force X Distance
Work and Power
Force: kilograms or pounds Distance: meters or feet Work: kilogram-meters or foot-pounds
International System of Measurement Force: newtons Distance: meters Work: newton-meters (joules)
Friction
Machines & Work
Friction
Friction is the property that causes objects to resist being moved across each other.
Friction always produces heat.
– Ex: Rubbing your hands together will produce heat that you can feel.
– Ex: Striking a match, flying a kite, and sanding wood
Friction
Soft materials produce more friction and heat than hard materials.
Rough surfaces produce more friction and heat than smooth surfaces.
It takes more force and friction to start an object moving than to keep it moving.
Friction
Without friction, we could not walk, run, drive, stop our cars, or do many other activities.
– Ex: Walking on ice is difficult because the smooth, glassy surface of the ice generates little friction.
Useful friction allows us to open jars and sand wood.
We use friction to make driving safe by putting sand and salt on icy roads, using chains, and keeping good tread on tires.
Friction
The less friction generated by a machine’s parts, the more efficient the machine is in doing work. Part of the work of a machine is to overcome friction, rather than to produce work.
Too much friction can become dangerous— parts of machines grind against each other and wear each other down.
Scientists have found many ways to reduce friction: adding lubricants (wax, oil, soap, grease) to make surfaces smoother.
Forms of Energy
Machines & Work
Forms of Energy
Energy is the ability to do work. Living things cannot survive without energy,
and machines cannot work without energy. There are many forms of energy, each of
which can be transformed from one form to another.
Forms of Energy
Electrical Energy – chemicals that produce electric current in a battery or from water turning generators
Heat Energy – combustion of chemicals Mechanical Energy – moving objects or other
substances (wind, water, and muscles)
Forms of Energy
Solar Energy – provides heat and light (sunlight) energy necessary for all life
Chemical Energy – chemicals react with oxygen or other chemicals, are transformed into heat, light, sound, or movement
Forms of Energy
Nuclear Energy – energy of the sun the produces light and heat; results from fusion or fission of atomic particles
Nuclear fission reactions can be controlled and are used to produce steam for turbines to turn electric generators
– Radioactive waste is an environmental problem associated with nuclear energy