Machines Lesson 4

Machines

Lesson 4

Focus Question

How do machines make tasks easier?

New Vocabulary

machine
effort force
resistance force
mechanical advantage
ideal mechanical advantage
efficiency
compound machine

Review Vocabulary

work: the transfer of energy that occurs when a
force is applied through a distance; equal to the
product of the system’s displacement and the
force applied to the system in the direction of
displacement

Benefits of Machines

• A machine is a device that makes

tasks easier by changing either the
magnitude or the direction of the
applied force.

• The force exerted by a user on a

machine is called the effort force
(Fe).

• The force exerted by the machine

is called the resistance force (Fr).

Multiple Select

A machine is a device the makes a task easier by

• changing the magnitude or direction of a force

• making tasks more complicated
• eliminating all tasks completely
• increasing workload and decreasing efficiency

Benefits of Machines

• The ratio of resistance force to effort force is

called the mechanical advantage (MA) of the
machine.

Mechanical Advantage

Multiple Choice

What is mechanical advantage?

• Mechanical advantage is the ratio of output force to input force in a machine.
• Mechanical advantage is the distance moved by the input force.
• Mechanical advantage refers to the weight of the machine itself.
• Mechanical advantage is the speed ratio of a machine.

Benefits of Machines

• A machine can increase force, but it cannot

increase energy.

• An ideal machine transfers all the energy, so the

output work equals the input work.

• Therefore, for an ideal machine, ideal

mechanical advantage (IMA) is equal to the
displacement of the effort force, divided by the
displacement of the load.

Ideal Mechanical Advantage

Multiple Choice

Which of the following statements best explains the concept of mechanical advantage?

• The ratio of output work to input work.

• The force exerted by the machine is divided by the effort force.

• The relationship between the displacement of the effort force and the displacement of the load.

• The total energy transferred by a machine during operation.

Multiple Choice

In a machine, if the effort force is 50 N and the resistance force is 200 N, what is the mechanical advantage (MA) of the machine?

• 0.25

• 1.5

• 2

• 4

Multiple Select

Why can a machine increase force but not energy?

• Machines are designed to conserve energy.

•  Energy is always lost to friction in machines.

• Machines can only transform energy, not create it

• Machines always double energy output

Benefits of Machines

• A machine’s design

determines its ideal
mechanical
advantage.

• For example, the

single pulley has an
ΙMA of 1, while the
two-pulley system
has an ΙMA of 2.

Benefits of Machines

• In a real machine, not all of the input work is

available as output work, and the machine is
less efficient at accomplishing the task.

• The efficiency of a machine (e) is defined as the

ratio of output work to input work.

Efficiency

Benefits of Machines

• Notice that efficiency can be expressed in terms

of the mechanical advantage and ideal
mechanical advantage.

• An efficient machine has an MA almost equal to

its ΙMA. A less efficient machine has a small MA
relative to its ΙMA.

Multiple Choice

If a machine has an ideal mechanical advantage (IMA) of 5 and an efficiency of 80%, what is its mechanical advantage (MA)?

• 4

• 5

• 6

• 7

Compound Machines

Most machines, no matter how complex, are
combinations of one or more of the six simple
machines.

Compound Machines

Compound Machines

Compound Machines

• A machine consisting of two or more simple machines

linked in such a way that the resistance force of one
machine becomes the effort force of the second is
called a compound machine.

• For example, in a bicycle, the pedal and the front gear

act like a wheel and axle. It is connected by the bike
chain to the rear gear and wheel which act as a
second wheel and axle.

Compound Machines

• The mechanical advantage of a compound machine is

the product of the mechanical advantages of the
simple machines from which it is made.

• MA = MA1 × MA2 × …

Multiple Choice

Consider a bicycle as a compound machine. Which of the following correctly describes how its mechanical advantage is calculated?

• By adding the mechanical advantages of each simple machine.

• By multiplying the mechanical advantages of each simple machine.

• By averaging the mechanical advantages of each simple machine.

• By dividing the mechanical advantage of the first machine by the second. 

Multiple Choice

A compound machine is made up of two simple machines. The first machine has MA = 0.64. The
second machine has MA = 0.23. What is the mechanical advantage of the compound machine?

• 0.43

• 0.89

• 0.15

• 0.57

The Human Walking Machine

• Movement of the human body is explained by the

same principles of force and work that describe all
motion.

• Simple machines, in the form of levers, give humans

the ability to walk and run.

The Human Walking Machine

• The components of lever systems

in the body include:
• A rigid bar
• A source of force
• A fulcrum or pivot
• A resistance

• The lever systems of the human

body are complex, not very
efficient, and have low mechanical
advantages.

Multiple Choice

Which of the following is NOT a component of a lever system in the human body? 

• Rigid bar

• Fulcrum

• Load 

•  Electrical motor

Multiple Choice

In the context of the presentation, which of the following best defines a compound machine?

• A machine that operates independently without any simple machines.

• A machine that consists of one simple machine only.

• A machine that consists of two or more simple machines working together.

•  A machine that has a mechanical advantage of 1.