compound machines

efficiency and mechanical advantage of compound machines

Because compound machines have more moving parts than simple machines, they generally have more friction to overcome. As a result, compound machines tend to have lower efficiency than simple machines. When a compound machine consists of a large number of simple machines, friction may become a serious problem, and it may produce a lot of heat. Lubricants such as oil or grease may be used to coat the moving parts so they slide over each other more easily. This is how a cars friction is reduced. Compound machines have a greater mechanical advantage than simple machines. Thats because the mechanical advantage of a compound machine equals the product of the mechanical advantages of all its component simple machines. The greater the number of simple machines it contains, the greater is its mechanical advantage.

kqed the science of riding a bicycle

Riding a bicycle might be easy. But the forces that allow humans to balance atop a bicycle are complex. QUEST visits Davis a city that loves its bicycles to take a ride on a research bicycle and explore a collection of antique bicycles. Scientists say studying the complicated physics of bicycling can lead to the design of safer, and more efficient bikes. For more information on the science of riding a bicycle, see MEDIA Click image to the left or use the URL below. URL:

textbook_image

what is a compound machine

A compound machine is a machine that consists of more than one simple machine. Some compound machines consist of just two simple machines. For example, a wheelbarrow consists of a lever, as you read earlier in the lesson "Simple Machines," and also a wheel and axle. Other compound machines, such as cars, consist of hundreds or even thousands of simple machines. Two common examples of compound machines are scissors and fishing rods with reels. To view a young students compound machine invention that includes several simple machines, watch the video at this link: . To see if you can identify the simple machines in a lawn mower, go to the URL below and click on Find the Simple Machines.

fishing rod with reel

The fishing rod with reel shown in Figure 16.25 is another compound machine. The rod is a third-class lever, with the fulcrum on one end of the rod, the input force close to the fulcrum, and the output force at the other end of the rod. The output distance is greater than the input distance, so the angler can fling the fishing line far out into the water with just a flick of the wrist. The reel is a wheel and axle that works as a pulley. The fishing line is wrapped around the wheel. Using the handle to turn the axle of the wheel winds or unwinds the line.

scissors

Look at the scissors in Figure 16.24. As you can see from the figure, scissors consist of two levers and two wedges. You apply force to the handle ends of the levers, and the output force is exerted by the blade ends of the levers. The fulcrum of both levers is where they are joined together. Notice that the fulcrum lies between the input and output points, so the levers are first-class levers. They change the direction of force. They may or may not also increase force, depending on the relative lengths of the handles and blades. The blades themselves are wedges, with a sharp cutting edge and a thicker dull edge.

textbook_image

instructional diagrams

No diagram descriptions associated with this lesson

questions

how greatly a machine increases the applied force

a. compound machine

-->  b. mechanical advantage

c. fishing rod

d. wheelbarrow

e. fishing reel

f. efficiency

g. scissors

Simple machines in a pair of scissors include

a. two levers.

b. two wedges.

c. one wheel and axle.

-->  d. two of the above

how well a machine deals with friction

a. compound machine

b. mechanical advantage

c. fishing rod

d. wheelbarrow

e. fishing reel

-->  f. efficiency

g. scissors

Compound machines include all of the following except a(n)

-->  a. chisel.

b. bicycle.

c. automobile.

d. wheelbarrow.

An axe is a compound machine that consists of a wedge and a(n)

a. screw.

b. inclined plane.

c. first class lever.

-->  d. third class lever.

example of a third class lever

a. compound machine

b. mechanical advantage

-->  c. fishing rod

d. wheelbarrow

e. fishing reel

f. efficiency

g. scissors

any machine that consists of more than one simple machine

-->  a. compound machine

b. mechanical advantage

c. fishing rod

d. wheelbarrow

e. fishing reel

f. efficiency

g. scissors

A compound machine tends to be less efficient than a simple machine because a compound machine

a. produces more work.

b. exerts a greater force.

-->  c. has more moving parts.

d. none of the above

example of a wheel and axle that works as a pulley

a. compound machine

b. mechanical advantage

c. fishing rod

d. wheelbarrow

-->  e. fishing reel

f. efficiency

g. scissors

Which of the following machines has the greatest mechanical advantage?

-->  a. mountain bike

b. inline skate

c. roller skate

d. tricycle

machine consisting of a wheel and axle and a lever

a. compound machine

b. mechanical advantage

c. fishing rod

-->  d. wheelbarrow

e. fishing reel

f. efficiency

g. scissors

machine consisting of two levers and two wedges

a. compound machine

b. mechanical advantage

c. fishing rod

d. wheelbarrow

e. fishing reel

f. efficiency

-->  g. scissors

A wheel and axle is an example of a compound machine.

a. true

-->  b. false

A pulley system that contains a fixed and a moveable pulley is a compound machine.

-->  a. true

b. false

A single pulley is less efficient than a pulley system that consists of two or more pulleys.

a. true

-->  b. false

The mechanical advantage of a compound machine is generally less than that of a simple machine.

a. true

-->  b. false

Friction tends to be a bigger problem in a compound machine than in a simple machine.

-->  a. true

b. false

Simple machines in a bicycle include

a. wheels and axles.

b. pulleys.

c. levers.

-->  d. all of the above

Which of the following is a compound machine?

a. wheel and axle

-->  b. scissors

c. pulley

d. lever

Which of the following machines contains one or more levers?

a. wheelbarrow

b. scissors

c. fishing rod

-->  d. all of the above

The fulcrum in a pair of scissors is always located

-->  a. between the input and output points.

b. closer to the input point.

c. closer to the output point.

d. two of the above

The mechanical advantage of a compound machine equals the

a. sum of the mechanical advantages of all its simple machines.

-->  b. product of the mechanical advantages of all its simple machines.

c. highest mechanical advantage of all its simple machines.

d. average mechanical advantage of all of its simple machines.

The way friction is reduced in a compound machine such as a car is with

a. fans.

b. heaters.

-->  c. lubricants.

d. none of the above

Some compound machines consist of thousands of simple machines.

-->  a. true

b. false

The output force is exerted by the handle ends of the levers in scissors.

a. true

-->  b. false

Scissors change the direction of the input force.

-->  a. true

b. false

The fulcrum in a fishing rod is at the center of the rod.

a. true

-->  b. false

Compound machines have more moving parts than simple machines.

-->  a. true

b. false

The fewer simple machines a compound machine contains, the greater its mechanical advantage.

a. true

-->  b. false

Compound machines have more friction to overcome than do simple machines.

-->  a. true

b. false

diagram questions

No diagram questions associated with this lesson