Effectively, four cables are pulling on the system of interest. Scissors are like a double-lever system. Which of the simple machines in Figure 1 and Figure 2 is most analogous to scissors? Suppose you pull a nail at a constant rate using a nail puller as shown in Figure 1.
Is the nail puller in equilibrium? What if you pull the nail with some acceleration — is the nail puller in equilibrium then? In which case is the force applied to the nail puller larger and why? Why are the forces exerted on the outside world by the limbs of our bodies usually much smaller than the forces exerted by muscles inside the body? Explain why the forces in our joints are several times larger than the forces we exert on the outside world with our limbs.
Can these forces be even greater than muscle forces see previous question? What is the mechanical advantage of a nail puller—similar to the one shown in Figure 1—where you exert a force 45 cm from the pivot and the nail is 1. What minimum force must you exert to apply a force of N to the nail? Suppose you needed to raise a kg mower a distance of 6. If you had a 2. A typical car has an axle with 1. What is its mechanical advantage assuming the very simplified model in Figure 3 b?
What force does the nail puller in Exercise 1 exert on the supporting surface? The nail puller has a mass of 2. If you used an ideal pulley of the type shown in Figure 4 a to support a car engine of mass kg, a What would be the tension in the rope? This pulley system has two cables attached to its load, thus applying a force of approximately 2T. Repeat Exercise 6 for the pulley shown in Figure 4 c , assuming you pull straight up on the rope.
Skip to main content. Statics and Torque. Search for:. Simple Machines Learning Objectives By the end of this section, you will be able to: Describe different simple machines.
Calculate the mechanical advantage. Example 1. What is the Advantage for the Wheelbarrow? Strategy Here, we use the concept of mechanical advantage. Discussion An even longer handle would reduce the force needed to lift the load. A lever is a bar resting on a pivot. Force effort applied at one point is transmitted across the pivot fulcrum to another point which moves an object load. The ideal mechanical advantage IMA - ignoring internal friction - of a lever depends on the ratio of the length of the lever arm where the force is applied divided by the length of the lever are that lifts the load.
The IMA of a lever can be less than or greater than 1 depending on the class of the lever. There are three classes of levers, depending on the relative positions of the effort is applied, load, and fulcrum. Wheel and axle. The wheel and axle is essentially a modified lever, but it can move a load farther than a lever can. The center of the axle serves as a fulcrum.
The ideal mechanical advantage IMA of a wheel and axle is the ratio of the radii. A pulley is a wheel over which a rope or belt is passed. It is also a form of the wheel and axle.
Pulleys are often interconnected in order to obtain considerable mechanical advantage. The ideal mechanical advantage IMA of a pulley is directly dependent upon the number of support strings, N. Inclined plane. The inclined plane is a simple device that hardly looks like a machine at all. The mechanical advantage increases as the slope of the incline decreases.
But the load will then have to be moved a greater distance. The ideal mechanical advantage IMA of an inclined plane is the length of the incline divided by the vertical rise, the so-called run-to-rise ratio.
The principle of work and kinetic energy also known as the work—energy principle states that the work done by all forces acting on a particle the work of the resultant force equals the change in the kinetic energy of the particle. Simple machines make work easier by multiplying, reducing, or changing the direction of a force.
Simple machines cannot change the amount of work done, but they can reduce the effort force that is required to do the work! For the inclined plane and lever, less effort effort force is needed to do the same work because the distance is increased. By using simple machines, the Egyptians were able to construct the pyramids. Inclined planes decrease the amount of force needed but more distance is required. By pushing an object up a slanted surface, one can move the object to height h with a smaller force than the weight of the object.
Actual Mechanical Advantage takes friction into account. As seen in the picture to the right, AMA is calculated by dividing the resistance force by the effort force. In other sources, you will see these labeled as output force and input force respectively. It is the output force of the simple machine. The input force is the same as the effort force put into moving the object using the machine. This formula for AMA is the same for the lever and the inclined plane.
A lever makes work easier by reducing the force needed to move a load by increasing the distance.
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