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Concept Day

SLIDE MACHINES-2-1

In this Investigation, we will focus on the simple machine, the lever, and prepare students for Investigation 2 lab. More specifically, in this Investigation, we will discuss first and second-class levers. In the following Investigation, we will discuss third-class levers.

We will begin with a brief review of the six types of simple machines. We will add to our previous discussion a bit more detail on the inclined plane and the screw.

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SLIDE MACHINES-2-2

• This introductory slide once again shows the six types of simple machines – the pulley, wheel and axle, the wedge, inclined plane, screw, and the lever.

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SLIDE MACHINES-2-3

• This is a review slide of the fixed pulley. It is important that you can identify the load force, load distance, effort force, and the effort distance. Remember that the effort distance is the distance over which the effort force is applied and not the distance from the pulley to the site of application of effort force. Further, load distance is the distance that the load is moved and not the distance from the pulley to the load.

Note: These definitions of effort distance and load distance are important to highlight at this time so that you are not confused with the effort arm and load arm when we turn our discussion to levers.

• The other important review item on this slide is the concept that mechanical advantage (MA) is Effort Distance divided by Load Distance or also Load Force divided by Effort Force. We will discuss mechanical advantage for each of the simple machines (except for the screw) in this review.

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SLIDE MACHINES-2-4

• This slide simply reviews the wheel and axle. It is identical to the slide discussed in Investigation 1. It is included here as a brief reminder of how mechanical advantage is achieved by a wheel and axle.

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SLIDE MACHINES-2-5

• This slide reviews the wedge. It is identical to the slide we used in the discussion of the wedge in Investigation 1. It is included here as a brief reminder of how mechanical advantage is achieved by a wedge.

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SLIDE MACHINES-2-6

• This slide introduces the simple machine, the inclined plane. As the examples show, an inclined plane essentially creates a slope from one level to the next. In the case of the truck ramp at the upper left, it provides a way to move the load (three boxes in this case) from ground level to the truck without having to lift the boxes that distance straight up. Depending on the mass of the load, direct lifting may be impossible.
• The staircase in the center is another example of an inclined plane. A single step from the first to the second floor would be extremely difficult! Therefore, an inclined plane need not be smooth.
• The inclined plane at the upper right is a bicycle ramp in Germany. Notice that an inclined plane need not be straight. In fact, as may be apparent by looking at this bicycle ramp, the screw is conceptually very similar to an inclined plane.
• Finally, at the lower left of the slide, we can see that determining the mechanical advantage of an inclined plane is a very simple process. We divide the length of the slope of the inclined plane by its height. This should be fairly obvious to you. Imagine, for example, if the length of the slope was cut in half, while the height remained the same. This is the situation shown on the lower right illustration. You should predict that it would be harder to push the box on the right up the slope than the one on the left. The fact that it would “feel” easier to push the box on the left-hand inclined plane is a good indication that it has a larger mechanical advantage.

Note: Notice that while less force is required to push the box up the left-hand inclined plane, one must push it twice as far as on the right-hand inclined plane. In the end, the exact same amount of work is required for both inclined planes.

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SLIDE MACHINES-2-7

• This slide introduces the simple machine, the screw.

Note: The conceptual basis of the screw is not any more complex than the other simple machines we have discussed. Essentially, the screw can be viewed as a long, narrow inclined plane wrapped around a cylinder. Your teacher may wish to simply highlight the use of screws and the fact that they are simple machines at this point. However, if your teacher or you wish to go further into screw function, the following material will be helpful.

• The formula for calculation a screw’s mechanical advantage is:

• r is radius of shaft
• l is the “lead” = the axial distance (parallel to shaft) the screw travels with one complete turn. In most types of screws, this is the distance between two consecutive threads.

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SLIDE MACHINES-2-8

• This slide begins our discussion of levers. It is similar to a slide from the previous Investigation. We will discuss levers much further in the next several slides. For reference, however, the nutcracker and bottle opener are second-class levers while the remaining tools are first-class levers.

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SLIDE MACHINES-2-9

• We will discuss the three classes of levers separately for the remainder of this Investigation and the next. However, this slide depicts all three of the levers we will study in the same place. With this slide up, the relative arrangement of the effort force, fulcrum, and load force are easily seen. Notice that in the first-class lever, the fulcrum is located between the effort force and the load. In the second-class lever, the load force is located between the effort force and the fulcrum. Finally, in the case of the third-class lever, which we will discuss further in Investigation 3, effort force is located between the load force and the fulcrum.

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SLIDE MACHINES-2-10

• This slide shows key elements of a first-class lever. In a first-class lever, the fulcrum is located between the effort force and load. The distance from the fulcrum to the effort force is called the effort arm. On the other hand, the distance between the load force and the fulcrum is referred to as the load arm.
• Examples of first-class levers are shown at the bottom of the slide. In addition, the location of the effort, fulcrum, and load are identified.
• This slide also shows the experimental setup for the first-class lever experiments that will be performed in Investigation 2 lab.

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SLIDE MACHINES-2-11

• This slide not only illustrates the experimental setup for the first-class lever experiments in Investigation 2 lab but also presents the data table from your Student Data Record and clearly shows where the data for each field of the Table is derived.

Note: You may wish to review this slide once again in preparation for Investigation 2 lab.

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SLIDE MACHINES-2-12

• This slide shows key elements of a second-class lever. In a second-class lever, the fulcrum is located at one end of the lever and the effort force is applied to the other. Therefore, the load is located between the effort force and the fulcrum. The distance from the fulcrum to the effort force is called the effort arm. The distance between the load force and the fulcrum is referred to as the load arm.
• Examples of second-class levers are shown at the bottom of the slide. The location of the effort, fulcrum, and load are indicated.
• This slide also shows the experimental setup for the second-class lever experiments that will be performed in Investigation 2 lab.

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SLIDE MACHINES-2-13

• This slide not only illustrates the experimental setup for the second-class lever experiments in Investigation 2 lab but also presents the data Table from your Student Data Record and clearly shows where the data for each field of the Table is derived.

Note: Again, you may wish to review this slide once again as a component of the PreLab and lab for this Investigation.

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