simple machines

simple and compound machines

There are six types of simple machines that are the basis of all other machines. They are the inclined plane, lever, wedge, screw, pulley, and wheel and axle. The six types are pictured in the Figure 1.4. Youve probably used some of these simple machines yourself. Most machines are combinations of two or more simple machines. These machines are called compound machines. An example of a compound machine is a wheelbarrow (see bottom of Figure 1.4). It consists of two simple machines: a lever and a wheel and axle. Many compound machines are much more complex and consist of many simple machines. Examples include washing machines and cars.

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increasing distance

Examples of machines that increase the distance over which force is applied are leaf rakes and hammers (see Figure which the force is applied, but it reduces the strength of the force.

changing the direction of force

Some machines change the direction of the force applied by the user. They may or may not also change the strength of the force or the distance over which the force is applied. Two examples of machines that work this way are the claw ends of hammers and flagpole pulleys. You can see in the Figure 1.3 how each of these machines works. In both cases, the direction of the force applied by the user is reversed by the machine. Q: If the pulley only changes the direction of the force, how does it make the work of raising the flag easier? A: The pulley makes it easier to lift the flag because it allows a person to pull down on the rope and add his or her own weight to the effort, rather than simply lifting the load.

how machines make work easier

Contrary to popular belief, machines do not increase the amount of work that is done. They just change how the work is done. Machines make work easier by increasing the amount of force that is applied, increasing the distance over which the force is applied, or changing the direction in which the force is applied. Q: If a machine increases the force applied, what does this tell you about the distance over which the force is applied by the machine: A: The machine must apply the force over a shorter distance. Thats because a machine doesnt change the amount of work and work equals force times distance. Therefore, if force increases, distance must decrease. For the same reason, if a machine increases the distance over which the force is applied, it must apply less force.

increasing force

Examples of machines that increase force are steering wheels and pliers (see Figure 1.1). Read below to find out how both of these machines work. In each case, the machine applies more force than the user applies to the machine, but the machine applies the force over a shorter distance.

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what is a machine

A machine is any device that makes work easier by changing a force. Work is done whenever a force moves an object over a distance. The amount of work done is represented by the equation: Work = Force x Distance When you use a machine, you apply force to the machine. This force is called the input force. The machine, in turn, applies force to an object. This force is called the output force. The output force may or may not be the same as the input force. The force you apply to the machine is applied over a given distance, called the input distance. The force applied by the machine to the object is also applied over a distance, called the output distance. The output distance may or may not be the same as the input distance.

instructional diagrams

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questions

work is calculated with the equation work = force/distance.

a. true

-->  b. false

the output distance of a machine is always

a) less than the input distance.

b) greater than the input distance.

c) equal to the input distance.

-->  d) none of the above

a machine increases the amount of work that is done.

a. true

-->  b. false

if a machine increases force, it must apply the force over a longer distance.

a. true

-->  b. false

machines that increase the distance over which force is applied include

a) steering wheels.

b) pliers.

-->  c) rakes.

d) two of the above

diagram questions

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