Efficiency. Efficiency is a measure of how much of the work put into a machine is changed into useful output work by the machine.

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1 Efficiency Efficiency is a measure of how much of the work put into a machine is changed into useful output work by the machine. A machine with high efficiency produces less heat from friction so more of the input work is changed to useful output work.

2 Calculating Efficiency Efficiency is usually expressed as a percentage by this equation:

3 Calculating Efficiency In an ideal machine there is no friction and the output work equals the input work. So the efficiency of an ideal machine is 100 percent. The efficiency of a real machine is always less than 100 percent.

4 Increasing Efficiency Machines can be made more efficient by reducing friction. This usually is done by adding a lubricant, such as oil or grease, to surfaces that rub together. A lubricant fills in the gaps between the surfaces, enabling the surfaces to slide past each other more easily.

5 Types of Simple Machines A simple machine is a machine that does work with only one movement of the machine. There are six types of simple machines: lever, pulley, wheel and axle, inclined plane, screw and wedge.

6 Levers A lever is a simple machine consisting of a bar that rotates around a fixed point. The fixed point of a lever is called the fulcrum. Like other machines, a lever makes work easier by changing the force applied to the machine or the distance over which the force is applied. The fixed point the lever pivots on is called the fulcrum. The input arm of the lever is the distance from the fulcrum to the point where the input force is applied. The output arm is the distance from the fulcrum to the point where the output force is exerted by the lever.

7 Levers How a lever changes force or distance depends on the location of the input and output forces relative to the fulcrum. The input force is the force applied by the user to the lever. The output force is the force applied by the lever to the object. If the output arm is shorter than the input arm, then the output force is greater than the input force.

8 Levers

9 Advantage of Third-Class Levers You may be wondering why you would use a third-class lever when it doesn t change the direction or strength of the applied force. The advantage of a third-class lever is that the output force is applied over a greater distance than the input force. The output end of the lever must move faster than the input end in order to cover the greater distance. Q: A broom is a third-class lever when it is used to sweep a floor, so the output end of the lever moves faster than the input end. Why is this useful? A: By moving more quickly over the floor, the broom does the work faster.

10 Ideal Mechanical Advantage of a Lever The IMA of a lever can be calculated from this equation:

11 Pulleys A pulley is a grooved wheel with a rope, chain, or cable running along the groove. The axle of the pulley acts as the fulcrum. Pulleys are generally used to lift objects, especially heavy objects. The object lifted by a pulley is called the load. The force applied to the pulley is called the effort.

12 Mechanical Advantage of a Pulley In a pulley, the ideal mechanical advantage is equal to the number of rope segments pulling up on the object. The more rope segments that are helping to do the lifting work, the less force that is needed for the job.

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14 Wheel and Axle A wheel and axle consists of two connected rings or cylinders, one inside the other. Both rings or cylinders turn in the same direction around a single center point. The inner ring or cylinder is called the axle, and the outer one is called the wheel. Besides the Ferris wheel, a doorknob is another example of a wheel and axle. In a wheel and axle, force may be applied either to the wheel or to the axle. A wheel and axle does not change the direction of the input force. However, the force put out by the machine, called the output force, is either greater than the input force or else applied over a greater distance.

15 Mechanical Advantage of the Wheel and Axle The output force is exerted at the rim of the axle. So the length of the output arm is the radius of the axle.

16 A sloping surface, such as a ramp that reduces the amount of force required to do work, is an inclined plane. Inclined Planes

17 Mechanical Advantage of an Inclined Plane By pushing a box up an inclined plane, the input force is exerted over a longer distance compared to lifting the box straight up.

18 The Screw A screw is an inclined plane wrapped in a spiral around a cylindrical post. You apply the input force by turning the screw. The output force is exerted along the threads of the screw. Screws move objects to a greater depth (or higher elevation) by increasing the force applied to the screw. Many screws are used to hold things together, such as two pieces of wood or a screw cap and bottle. When you use a screw, you apply force to turn the inclined plane. The screw, in turn, applies greater force to the object, such as the wood or bottle top.

19 Mechanical Advantage of a Screw The force applied by the screw (output force) is always greater than the force applied to the screw (input force). Therefore, the mechanical advantage of a screw is always greater than 1. In the screw on the right, the threads of the inclined plane are closer together. This screw has a greater mechanical advantage and is easier to turn than the screw on the left, so it takes less force to penetrate the wood with the right screw. The trade-off is that more turns of the screw are needed to do the job because the distance over which the input force must be applied is greater.

20 The Wedge A wedge consists of two inclined planes, giving it a thin end and thick end. A wedge is used to cut or split apart objects. Force is applied to the thick end of the wedge, and the wedge, in turn, applies force to the object along both of its sloping sides. This force causes the object to split apart. It changes the direction of the input force.

21 Examples

22 Mechanical Advantage of a Wedge A wedge applies more force to the object (output force) than the user applies to the wedge (input force), so the mechanical advantage of a wedge is greater than 1. A longer, thinner wedge has a greater mechanical advantage than a shorter, wider wedge. With all wedges, the trade-off is that the output force is applied over a shorter distance, so force may need to be applied to the wedge repeatedly to push it through the object.

23 Compound Machines Two or more simple machines that operate together form a compound machine. A car is a compound machine. Burning fuel in the cylinders of the engine causes the pistons to move up and down.