Simple Machines PDF

## 2.1 Simple Machines Although many modern machines are large and complex, they usually operate on the basic principles of simple machines, principles that have been used for centuries. - In museums we often see early tools and weapons whose sharp edges are examples of a simple machine (a wedge...

## 2.1 Simple Machines Although many modern machines are large and complex, they usually operate on the basic principles of simple machines, principles that have been used for centuries. - In museums we often see early tools and weapons whose sharp edges are examples of a simple machine (a wedge). - The early Egyptians used ramps to move blocks when building pyramids; ramps are also an example of a simple machine (inclined planes). - Even today, the ancient technology of pulleys and levers is often used to raise water out of rivers and wells. ### Understanding Concepts 1. State the main function or functions of each of the following machines: * an axe * a tennis racket * a round doorknob * a screwdriver 2. Give two or three examples, not found in the text, of simple machines in the kitchen that increase the force you apply. ## The Lever Family of Machines A lever is a rigid bar that can rotate freely around a support called a fulcrum. A seesaw (or teeter-totter) is a typical example of a lever. - An effort force, *Fe*, is a force applied to one part of a lever to move a load at another part; the load exerts a load force, *Fl*. - Two other variables are measured on levers: - The perpendicular distance from the fulcrum to the effort force, the **effort arm**, symbol *de*. - The perpendicular distance from the fulcrum to the load force, the **load arm**, symbol *dl*. **Lever** - a rigid bar that can rotate freely around a fulcrum **Fulcrum** - a support around which a lever can rotate or pivot **Effort force** - a force applied to one part of a lever to move a load at another part; symbol *Fe* **Load force** - the force exerted by the load on a lever; symbol *Fl* **Effort arm** - the perpendicular distance from the fulcrum to the effort force; symbol *de* **Load arm** - the perpendicular distance from the fulcrum to the load force; symbol *dl* Levers are divided into three classes, depending on the positions of the load, the effort force, and the fulcrum: * **First-class lever** - the fulcrum is between the load and the effort force. * **Second-class lever** - the load is between the fulcrum and the effort force. * **Third-class lever** - the effort force is exerted between the fulcrum and the load. **First-class lever** - a lever with the fulcrum between the load and the effort force **Second-class lever** - a lever with the load between the fulcrum and the effort force **Third-class lever** - a lever with the effort force exerted between the fulcrum and the load ## Biomechanical Systems Biomechanical systems, which are systems involving a living body, can also be understood as simple machines. - An example is the human forearm, which works as a third-class lever. - The action of the forearm can be analyzed and then closely copied to create robotic arms. - Other examples of biomechanical systems are your lower legs, animal jaws, bird beaks, and the claws of crayfish and hawks. **Biomechanical system** - a system of a living body ## The Wheel and Axle A wheel and axle is a large-diameter, rigid, circular disk (the wheel) connected to a small-diameter, rigid rod (the axle). - Both the wheel and the axle rotate around a fulcrum, so this machine is also part of the lever family. - Gears are toothed wheels of different diameters linked together to increase or decrease speed or to change direction. - A pair of gears resembles a wheel and axle because each gear rotates around a fulcrum. Gears can be linked together directly at their rigid teeth, or they can be linked with a chain, as on a bicycle. **Pulley** - a wheel with a grooved rim in which a rope or cable can run **Wheel and axle** - a large-diameter, rigid disk connected to a small-diameter rigid rod **Gears** - toothed wheels of different diameters linked together to change the speed or direction moved ## The Inclined Plane Family of Machines The inclined plane and related machines are shown in Figure 8. An inclined plane is a ramp that increases the load that can be moved by an effort force. - The force required to move an object up a ramp is less than the force needed to lift the object vertically upward. - A wedge is a double inclined plane that increases the applied force. - A screw is an inclined plane wrapped around a central shaft. It too increases the applied force. **Inclined plane** - a ramp that increases the load that can be raised by an effort force **Wedge** - a double inclined plane that increases the applied or effort force **Screw** - an inclined plane wrapped around a central shaft that increases the applied or effort force **Compound machine** - a machine made of two or more simple machines ## Understanding Concepts 1. State which simple machine forms the basis of each of the following: * a doorstop, with the pointed end placed between the floor and the bottom of the door * an escalator * a mountain highway * a hand-held pencil sharpener 2. Explain how the parts of the bicycle shown in Figure 6, page 73, form a compound machine made up of gears and another simple machine. ## Making Connections You have been asked to design a two-level bridge over a river. One level is for trains and the other is for cars, trucks, and buses. Which would you place in the upper level? (Hint: Think of the forces required to go up an inclined plane.) Explain your answer. Draw a diagram to illustrate your design. ## SUMMARY Simple Machines * A machine helps us perform tasks by performing one or more of five main functions. * The lever family of machines consists of the lever, the pulley, the wheel and axle, and gears. * The inclined plane family of machines consists of the inclined plane, the wedge, and the screw. * Compound machines and biomechanical systems can be analyzed in terms of simple machines. ## Understanding Concepts 1. Name the simple machine(s) associated with each of the following: * a water slide * a triple beam balance * a tricycle * a letter opener * the screw cap on a water bottle * a skateboard 2. a. Explain why a wheel and axle system is considered a member of the lever family of machines. b. Explain why a screw is considered a member of the inclined plane family of machines. 3. How are gears similar to a wheel and axle? How are they different? 4. For a wheel and axle system, on which part would you apply the effort force in order to: * increase the force? * increase the distance or speed? 5. State the class of lever of each biomechanical system in Figure 11. 6. a. When an axe is used as a wedge to split a log, how does the direction of the load force compare to the direction of the effort force? Draw a sketch to illustrate your answer. b. Axes used to split logs are heavier than axes used to chop down trees. Explain why. ## Applying Inquiry Skills 7. Cut a sheet of paper diagonally in half to create two right-angled triangles. Wrap one of the triangles around a pencil in a way that illustrates one type of simple machine. Explain which machine it is and why. ## Making Connections 8. Before the wheel and axle system was invented, people used logs to move large stones and other heavy objects. Explain how straws or pencils can be used to model this ancient form of the wheel. 9. Choose one of the following topics to research, and write a summary of what you discover. Relate your findings to simple machines. * Early inhabitants of Easter Island (an island in the South Pacific, called Rapa Nui locally) used simple machines to move huge volcanic rocks. The inhabitants then carved these rocks into figures of heads. * An estimated 4500 years ago, inhabitants of southern England transported huge stones to build stone circles such as the famous Stonehenge. Scientists are trying to recreate the trip using only simple machines.