![]() Pulley systems are often used to raise flags and window blinds and are part of the mechanism of construction cranes. To raise a load 1 meter with a pulley system you have to pull N meters of rope. Once again we have to exert force over a longer distance to multiply force. Simply count the number of ropes supporting the load. Of all simple machines, mechanical advantage is easiest to calculate for pulleys. Ask for an explanation of the 2 π π in the equation for IMA.įigure 9.11 shows three different pulley systems. Ask students how the forces exerted by a wood screw are different from those exerted by the screw in Figure 9.9. Have the students compare this screw to a wood screw and a circular stairway. Devices like the one shown in Figure 9.9 are used to lift cars and even houses. Explain that the combined mechanical advantage can be great. Suggest that a screw is classified as a separate type of simple machine perhaps because it looks so different from what it really is-an inclined plane which sometimes is turned by a lever. The equation for IMA is shown in Figure 9.7(b). The ideal mechanical advantage, IMA, is the mechanical advantage of a perfect machine with no loss of useful work caused by friction between moving parts. The mechanical advantage is a number that tells us how many times a simple machine multiplies the effort force. The triangular pivot is called the fulcrum the part of the lever between the fulcrum and F e is the effort arm, L e and the part to the left is the resistance arm, L r. The effort force, applied at F e, lifts the load (the resistance force) which is pushing down at F r. ![]() Figure 9.7(b) shows the how a lever works mathematically. In Figure 9.7(a), the worker uses a type of lever to exert a small force over a large distance, while the pry bar pulls up on the nail with a large force over a small distance. Let’s examine how this works in practice. The down side is that you must exert the force over a greater distance, because the product of force and distance, f d, (which equals work) does not change. In most cases, a simple machine is used to reduce the amount of force you must exert to do work. So, why is a simple machine useful? Although it cannot change the amount of work you do, a simple machine can change the amount of force you must apply to an object, and the distance over which you apply the force. A machine cannot increase the amount of energy you put into it. Why can’t simple machines change the amount of work that you do? Recall that in closed systems the total amount of energy is conserved. Simple machines make work easier, but they do not decrease the amount of work you have to do. This is the underlying principle of all simple machines. Because the amount of work is not changed, the term f d does not change, but force can decrease if distance increases. Explain that the product of force and distance is critical to understanding simple machines. Explain that simple machines are often hand-held, and that they reduce force, not work. Be sure students do not equate machines and motors by asking for (and, if necessary, providing) examples of machines that are not motorized. Dispel any misconceptions that machines reduce the amount of work. Ask the students what they know about machines and work. Reduces wood splitting and superior holding power.In this section you will apply what you have learned about work to find the mechanical advantage and efficiency of simple machines. Coated fasteners ideal for pressure treated lumber applications and for all outdoor wood construction such as decking, patios, lawn furniture, window boxes. XGT's QuickGrab point means super-fast starts. XGT's unique engineering reduces wood splitting and provides superior holding power. Grabber's XGT professional exterior grade GrabberGard coated fasteners are ideal for pressure treated lumber applications and for all outdoor wood construction such as decking, patios, lawn furniture, window boxes and more. Reduces wood splitting and superior holding power. Suitable for use in non-coastal areas with all pressure-treated lumbers including ACQĭeck screws torx drive type 17 point flat head gauge x lgth 8 inches x 2-1/2 qty=2.5m Coated fasteners ideal for pressure treated lumber applications and for all outdoor wood construction such as decking, patios, lawn furniture, window boxes.Layers are bonded together through thermal fusion and this unique method of combining layers results in a combination of the coating films.Distinguishing feature of GrabberGard is the joining and encapsulation the substrate with the fused organic surface coating.Duplex coating constituting a zinc substrate and organic polymer topcoat.GrabberGard metal finish is a high-grade proprietary metal surface processing technology that prevents corrosion.Flat head is fully seated when the head is flush with the work surface.
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