Simple Machines

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Simple Machines in Cars

Inclined Plane

An inclined plane is a simple machine with no moving parts. It is simply a straight slanted surface set at an angle (other than a right angle) against a horizontal surface used to raise an object. Examples of inclined planes include ramp, slanted road, slide, and path up a hill.

The following figure shows an inclined plane. The length A is the base, length B is the height, and length C is the inclined plane. With the use of the inclined plane a given resistance can be overcome with a smaller force than if the plane is not used. For example, in the figure, suppose we wish to raise a weight of 100 kg through the vertical distance B = 2 m. If this weight were raised vertically and without the use of the inclined plane the force 100 kg would have to be exerted through the distance B. However, if the inclined plane is used and the weight is moved over the inclined plane C, a force of only 2/3 of 100 kg or 66.7 kg is required. Remember, this force is exerted through a distance C which is greater than distance B.

Using an inclined plane requires a smaller force exerted through a greater distance to do a certain amount of work. Letting F represent the force required to raise a given weight on the inclined plane, and W the weight to be raised, we have the proportion:

In our daily life, lifting an object straight up is heavier than pulling it up an incline plane, we do not need to use as much force. However, the inclined plane is longer. Inclined planes can also be used in reverse to slow things down to a stop. It is easy to find applications of inclined planes everywhere: Ramps for wheelchairs, steps, a ski jump, car ramps, playground slide, boat ramps, etc.

Wheels

The gear, the wheel and axle, and the pulley are all kinds of wheels, with small alterations. A gear is a wheel with accurately machined teeth round its edge. Its purpose is to transmit rotary motion and force. Basic relationships for a gear are the number of teeth, the diameter, and the rotary velocity of gears. Gears being an important part of a machine have many applications within various industries. These industries include automotive industries, steel plants industry, paper industry, in mining and many more. They are used as conveyors, elevators, separators, cranes and lubrication systems.

The following figure shows the ends of two shafts A and B connected by 2 gears of 12 and 24 teeth respectively. The larger gear will make only one-half turn while the smaller makes a complete turn. That is, the ratio of speeds (velocity ratio) of the large to the smaller is as 1 to 2. The gear that is closer to the source of power is called the driver, and the gear that receives power from the driver is called the driven gear. The ratio between the rotation speed of the driven gear and the rotation speed of the driver is called the gear ratio.

Levers

Another basic mechanism is the lever, a bar which rests, or pivots, on a fulcrum. A seesaw is a familiar example of a lever in which one weight balances the other. The hammer is another example of lever when it is used to pull a nail out of a piece of wood.

All levers have at least two basic purposes. One is to lift or move a load at one place on the lever by making an effort at another location of the bar. The second is to apply a force to an object by exerting the force elsewhere.

Levers can be used to change the distance and power of movement. All levers have three basic parts: the fulcrum, a force or effort, and a weight.

There are three types of levers as shown in the figure. The location of the fulcrum in relation to the resistance (or weight) and the effort determine the lever class.

Common examples of first-class levers include crowbars, scissors, pliers, tin snips and playground seesaws. Examples of second-class levers include nut crackers, wheel barrows, and certain types of bottle openers. The human bicep muscle is an example of a third class lever.

Screws

A screw is a shaft with a thread or groove wrapped around it to form a helix. While turning, a screw converts a rotary motion into a forward or backward motion.  By rotating the screw (applying a torque), the force is applied perpendicular to the groove, therefore translating a rotational force into a linear one. It is frequently used to fasten objects together.

Wedges

The wedge allows motion from objects such as hammers to be transferred into a breaking, cutting, or splitting motion. The force is perpendicular to the inclined surfaces, so it pushes two objects (or portions of a single object) apart. A wedge converts motion in one direction into a splitting motion that acts at right angles to the blade. Nearly all cutting machines use the wedge including knifes. A lifting machine may use a wedge to get under a load.

Belt and Pulleys

Belts and pulleys are an important part of most machines. Pulleys are gears without teeth and instead of running together directly they are made to drive one another by cords, ropes, cables, or belting of some kinds. As with gears, the velocities of pulleys are inversely proportional to their diameters. Examples of where pulleys can be used include flag poles, sailboats, blinds, and cranes. The following figure shows belt and pulleys. Pulleys can also be arranged as a block and tackle.

Focus on Engineering

 Simple machines are common today in the form of various tools . The same physical principles and mechanical application of simple machines used by ancient engineers to build pyramids are employed by modern engineers to construct various structures such as houses, roads, bridges, and skyscrapers.