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Review simple machines: lever, pulley, wheel, inclined plane, wedge, screw

Simple machines are fundamental tools that make work easier by changing the direction or magnitude of a force. They are the building blocks of many complex machines and are essential in understanding how mechanical systems operate. The six basic types of simple machines are the lever, pulley, wheel and axle, inclined plane, wedge, and screw. Each of these machines helps to reduce the effort needed to perform tasks by providing a mechanical advantage. Understanding simple machines is crucial because they form the basis for more advanced mechanical systems and are widely used in everyday life and in various industries. By studying simple machines, we gain insights into the principles of physics and engineering that govern the operation of more complex devices.

Figures (8)

Pulley in oil derrick
Figure 12.2 Torque of a force: (a) When the torque of a force causes counterclockwise rotation about the axis of rotation, we say that its sense is positive, which means the torque vector is parallel to the axis of rotation. (b) When torque of a force causes clockwise rotation about the axis, we say that its sense is negative, which means the torque vector is antiparallel to the axis of rotation.
Figure 12.3 The distribution of mass affects the position of the center of mass (CM), where the weight vector w→w→ is attached. If the center of gravity is within the area of support, the truck returns to its initial position after tipping [see the left panel in (b)]. But if the center of gravity lies outside the area of support, the truck turns over [see the right panel in (b)]. Both vehicles in (b) are out of equilibrium. Notice that the car in (a) is in equilibrium: The low location of its center of gravity makes it hard to tip over.
Figure 12.4 The weight distribution between the axles of a car. Where is the center of gravity located? (credit "car": modification of work by Jane Whitney)
Figure 12.5 The free-body diagram for the car clearly indicates force vectors acting on the car and distances to the center of mass (CM). When CM is selected as the pivot point, these distances are lever arms of normal reaction forces. Notice that vector magnitudes and lever arms do not need to be drawn to scale, but all quantities of relevance must be clearly labeled.
Figure 12.6 The equivalent free-body diagram for the car; the pivot is clearly indicated.
Figure 12.7 Mass is added gradually to the pan until one of the strings snaps.
Figure 12.8 Free-body diagram for the knot in Example 12.2.

A lever is a bar that turns around a fixed point called a fulcrum. It helps lift or move objects by applying force at one end. A pulley uses a rope and a wheel to change the direction of a force, making it easier to lift things.

The wheel and axle work together to move objects over a surface with less friction. An inclined plane is a sloping surface that helps move objects up or down with less effort. A wedge is like two inclined planes back to back, used to split or hold things apart.

A screw is an inclined plane wrapped around a cylinder, used to hold things together or lift materials. Understanding these machines helps explain how bigger machines and tools work. They are used in everyday life, from opening jars to building bridges.

By learning how these simple machines work, you can better understand more complex systems in science and engineering.

Key Points

  • A lever is a rigid bar that pivots around a fixed point called a fulcrum, used to lift or move loads by applying force at one end.
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