Today's availability of electricity and technologically-advanced machines make it difficult for us to see what the simple machine is accomplishing. But in the context of ancient Egypt, the simple machines that we will study are the much more basic tools of the time. After we develop an understanding of simple machines, we will shift our context to building a skyscraper in the present day, so we can compare and contrast how simple machines were used across the centuries and are still used today. Show the PowerPoint presentation, or print out the slides to use with an overhead projector.
The presentation is animated to promote an inquiry-based style; each click reveals a new point about each machine; have students suggest characteristics and examples before you reveal them. Simple machines are everywhere; we use them everyday to perform simple tasks. Simple machines have also been in use since the early days of human existence.
While simple machines take many shapes, they come in six basic types:. We use simple machines because they make work easier. The scientific definition of work is the amount of force that is applied to an object multiplied by the distance the object is moved. Thus, work consists of force and distance. Each job takes a specific amount of work to finish it, and this number does not change.
Thus, the force times the distance always equals the same amount of work. This means that if you move something a smaller distance you need to exert a greater force.
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On the other hand, if you want to exert less force, you need to move it over a greater distance. This is the force and distance trade off, or mechanical advantage , which is common to all simple machines. With mechanical advantage, the longer a job takes, the less force you need to use throughout the job. Most of the time, we feel that a task is hard because it requires us to use a lot of force. Therefore, using the trade off between distance and force can make our task much easier to complete. The wedge is a simple machine that forces objects or substances apart by applying force to a large surface area on the wedge, with that force magnified to a smaller area on the wedge to do the actual work.
A nail is a common wedge with a wide nail head area where the force is applied, and a small point area where the concentrated force is exerted. The force is magnified at the point, enabling the nail to pierce wood.
As the nail sinks into the wood, the wedge shape at the point of the nail moves forward, and forces the wood apart. Figure 1: An axe is an example of a wedge. All rights reserved.
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Everyday examples of wedges include an axe see Figure 1 , nail, doorstop, chisel, saw, jackhammer, zipper, bulldozer, snow plow, horse plow, zipper, airplane wing, knife, fork and bow of a boat or ship. The wheel and axle is a simple machine that reduces the friction involved in moving an object, making the object easier to transport. When an object is pushed, the force of friction must be overcome to start it moving. Once the object is moving, the force of friction opposes the force exerted on the object.
The wheel and axle makes this easier by reducing the friction involved in moving an object. The wheel rotates around an axle essentially a rod that goes through the wheel, letting the wheel turn , rolling over the surface and minimizing friction. Wouldn't it be easier to roll it along using logs placed underneath the stone? Everyday examples of the wheel and axle include a car, bicycle, office chair, wheel barrow, shopping cart, hand truck and roller skates.
A lever simple machine consists of a load, a fulcrum and effort or force. The load is the object that is moved or lifted. The fulcrum is the pivot point, and the effort is the force required to lift or move the load.
By exerting a force on one end of the lever the applied force , a force at the other end of the lever is created. The applied force is either increased or decreased, depending on the distance from the fulcrum the point or support on which a lever pivots to the load, and from the fulcrum to the effort. Figure 2: A crowbar is an example of a lever. Everyday examples of levers include a teeter-totter or see-saw, crane arm, crow bar, hammer using the claw end , fishing pole and bottle opener.
Think of a how you use a crowbar see Figure 2. By pushing down on the long end of the crowbar, a force is created at the load end over a smaller distance, once again, demonstrating the tradeoff between force and distance. Inclined planes make it easier to lift something. Think of a ramp.noroi-jusatsu.info/wp-content/2019-11-26/3501-telecharger-logiciel-espion.php
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Engineers use ramps to easily move objects to a greater height. There are two ways to raise an object: by lifting it straight up, or by pushing it diagonally up. Lifting an object straight up moves it over the shortest distance, but you must exert a greater force. On the other hand, using an inclined plane requires a smaller force, but you must exert it over a longer distance. Everyday examples of inclined planes include highway access ramps, sidewalk ramps, stairs, inclined conveyor belts, and switchback roads or trails.
Figure 3: A car jack is an example of a screw-type simple machine that enables one person to lift up the side of a car.
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A screw is essentially an inclined plane wrapped around a shaft. Screws have two primary functions: they hold things together, or they lift objects. A screw is good for holding things together because of the threading around the shaft. The threads grip the surrounding material like teeth, resulting in a secure hold; the only way to remove a screw is to unwind it. A car jack is an example of a screw being used to lift something see Figure 3. Everyday examples of screws include a screw, bolt, clamp, jar lid, car jack, spinning stool and spiral staircase.
Figure 4: A pulley on a ship helps people pull in a heavy fishing net. A pulley is a simple machine used to change the direction of a force. Think of raising a flag or lifting a heavy stone. To lift a stone up into its place on a pyramid, one would have to exert a force that pulls it up. By using a pulley made from a grooved wheel and rope, one can pull down on the rope, capitalizing on the force of gravity, to lift the stone up.
Even more valuable, a system of several pulleys can be used together to reduce the force needed to lift an object. Everyday examples of pulleys in use include flag poles, elevators, sails, fishing nets see Figure 4 , clothes lines, cranes, window shades and blinds, and rock climbing gear. A compound machine is a device that combines two or more simple machines. For example, a wheelbarrow combines the use of a wheel and axle with a lever.
Using the six basic simple machines, all sorts of compound machines can be made. There are many simple and compound machines in your home and classroom. Watch this activity on YouTube. Today, we have discussed six simple machines.
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Who can name them for me? Answer: Wedge, wheel and axle, lever, inclined plane, screw, and pulley. How do simple machines make work easier? Answer: Mechanical advantage enables us to use less force to move an object, but we have to move it a longer distance. Why do engineers use simple machines? Possible answers: Engineers creatively use their knowledge of science and math to make our lives better, often using simple machines.
They invent tools that make work easier. They accomplish huge tasks that could not be done without the mechanical advantage of simple machines.