Today we are going to take a closer look at two simple machines — the inclined plane and the screw. How do you think they may have helped build the ancient pyramids? Following the lesson refer to the activity Watch It Slide! The mechanical advantage of a machine is the ratio of the load to the applied force.
In other words, mechanical advantage determines how much force we need to perform a task. For example, the greater the mechanical advantage of a machine, the less force we need to have to perform a task such as moving an object. The opposite is true as well. A good mechanical advantage is one that is greater than 1. The purpose of an inclined plane as a simple machine is to move something from a lower height to a higher height with less effort.
An object simply placed on a tilted surface often slides down the surface see Figure 1 because of the force in the downhill direction. In other words, the forces in this scenario are unbalanced i.
The rate at which the object slides down is dependent upon how tilted the surface is; the greater the tilt of the surface, the faster the rate at which the object will slide down it. This is measured by the angle of inclination. Students can find this using a protractor. Friction also affects the movement of an object on a slope.
Friction is a force that offers resistance to movement when one object is in contact with another. Imagine now that you were on the downside of the object and applying force to keep the object in the same place not moving.
To keep the object stationary, the force you would have to apply would need to equal the downward force due to gravity. That would be an example of balanced forces.
If you wanted to push the force upwards, you would need to exceed the force of gravity. Figure 1: This diagram shows how ancient cultures used inclined planes to move heavy stones to the top of their pyramids. The force of gravity, friction and the pull force all affect how easy or hard it is to pull the cart up the inclined plane.
To understand an object's motion on an inclined plane, it is important to analyze the forces acting upon it. The force of gravity also known as weight acts in a downward direction. When the angle of inclination is greater, and the slope is steeper there is more weight component to overcome.
With a shallower slope the weight component is easier to overcome and requires less effort. The mechanical advantage of an inclined plane depends upon its slope and height. To find the ideal mechanical advantage of an inclined plane, divide the length of the slope by its height. An inclined plane produces a mechanical advantage to decrease the amount of force needed to move an object to a certain height; it also increases the distance the object must move.
The object moving up an inclined plane needs to move the entire length of the slope of the plane to move the distance of the height. For example, if you have a ramp with a slope length 20 meters that rises 5 meters high, then your trade-off is moving the 20 meters distance versus lifting straight up 5 meters, and your ideal mechanical advantage is 4. A screw is a simple machine that has two purposes. It can be used to fasten two or more objects together or it can be used to lift up a heavy object.
In most applications, a lever is used to turn the screw. A good example of this is a screwdriver. It is the circumference of the lever or screwdriver and the pitch of the screw that determines the mechanical advantage of the screw.
The pitch of a screw is the distance between adjacent threads on that screw. The pitch can be calculated by dividing a certain distance by the number of threads on screw. One complete revolution of the screw into an object is equal to the distance of the pitch of a screw.
The ideal mechanical advantage of a screw is found approximately by dividing the circumference of the lever by the pitch of the screw. Today, we learned about two simple machines; the inclined plane and the screw.
Who can give me an example of an inclined plane? Possible answers: Ramp, staircase, escalator. How does an inclined plane help us do work? Possible answer: We push objects up an inclined plane. What is the trade-off?
Answer: Distance What are two ways screws are used? Answer: To fasten objects or to lift something. What other simple machine often helps us use a screw? Answer: A lever. What has an engineer designed that uses an inclined plane or a screw? Possible answers: Parking garage, ramp, escalator, drilling rig, holding parts of something together, such as an airplane or MP3 player.
In other lessons of this unit, students study each simple machine in more detail and see how each could be used as a tool to build a pyramid or a modern building. To deviate from the horizontal. Usually a straight slanted surface and no moving parts, such as a ramp, sloping road or stairs. Making the task easier which means it requires less force , but may require more time or room to work more distance, rope, etc. For example, applying a smaller force over a longer distance to achieve the same effect as applying a large force over a small distance.
The ratio of the output force exerted by a machine to the input force applied to it. Mesoamerica: A region extending south and east from central Mexico to include parts of Guatemala, Belize, Honduras and Nicaragua. In pre-Columbian times it was inhabited by diverse civilizations, such as the Mayan and the Olmec. The typical shape is a square or rectangular base at the ground with sides faces in the form of four triangles that meet in a point at the top.
Mesoamerican temples have stepped sides and a flat top surmounted by chambers. Often a cylindrical rod incised with a spiral thread. For example, a wedge, wheel and axle, lever, inclined plane, screw, or pulley. The amount or degree of deviation from the horizontal.
On a large sheet of paper or on the classroom board, draw a chart with the title "Simple Machines: Inclined Planes and Screws. Fill out the K and W sections during the lesson introduction as facts and questions emerge.
Fill out the L section at the end of the lesson. List all of the things students learned about inclined planes and screws and their mechanical advantages. Were all of the W questions answered? What new things did they learn?
Closing Discussion: Ask students to explain why it is easier to pull a cart or block up a long, shallow ramp than taking it up steps, a ladder or a steep ramp.
Ask them to give examples of mechanical advantage using an inclined plane or a screw. It reduces the force necessary to move a load a certain distanc'e up by providing a path for the load to move at a low angle to the ground. This lessens the needed force but increases the distance involved, so that the amount of work stays the same. Examples are ramps, sloping roads, chisels, hatchets, plows, air hammers, carpenter's planes and wedges.
The most canonical example of an inclined plane is a sloped surface; for example a roadway to bridge a height difference. The inclined plane is used to reduce the force necessary to overcome the force of gravity when elevating or lowering a heavy object. The ramp makes it easier to move a physical body vertically by extending the distance traveled horizontally run to achieve the desired elevation change rise.
Others may also call it tilt. Ramps are used as an alternative for a stairway for wheelchairs, buggies and shopping carts. Ramps may zigzag. The force required to lift the boat to land is considerably less, but the distance needed to pull the boat is much longer. The mechanical advantage for a ramp is the ratio of the force applied to the output force.
By conservation of energy , the mechanical advantage can be expressed in terms of the distance traveled. This means that the longer the plane gets, the easier the task will be in terms of force, but the distance will always have to change in proportion. Remember that this is only for an ideal ramp, where there are no non-conservative forces acting on the object.
There is never a time in reality when friction can be ignored fully, so the true mechanical advantage will always be less than the ideal mechanical advantage.
While ramps are used all the time even stairs are a effectively a form of ramp , friction on the ramp creates situations where there's an upper limit to how helpful they are in saving effort.
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