A compound machine is a machine that consists of more than one simple machine. Compound machines such as a wheelbarrow or corkscrew consist of just two simple machines. Big compound machines such as cars consist of hundreds or thousands of simple 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,... Show more

A compound machine is a machine that consists of more than one simple machine. Compound machines such as a wheelbarrow or corkscrew consist of just two simple machines. Big compound machines such as cars consist of hundreds or thousands of simple 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 car's friction is reduced.    
Compound machines have a greater mechanical advantage than simple machines. That's 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.   

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