Simple Lifting Machines

Simple Lifting Machines

Unit 1: Engineering Principles

​Lesson Objectives

Examples of simple lifting machines​

Examples of simple lifting machines​

What is a simple lifting machine?​

​A simple lifting machine is any machine that is designed to enable a load (F_L) to be raised by a much smaller effort (F_E).

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​This is achieved by increasing the distance travelled by the effort (s_E) when compared to the distance travelled by the load (s_L)

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​This way the work done by the load (W_L) is similar or less than the work done by the effort (W_E)

What is a simple lifting machine?​

​We know that the formula for work done is:

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W = F x s

​Parameters of Simple Lifting Machines

​Mechanical Advantage (M.A)

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​The ratio of F_L to F_E is called the mechanical advantage:

​As M.A is a ratio of two forces, it is a dimensionless quantity which means it has no units

Multiple Choice

Example Problem - Part 1/3

A lifting machine raises a crate of mass 160 kg with an applied effort of 200N. Calculate the mechanical advantage of the machine

• 785

• 78.5

• 7.85

• 0.785

​Parameters of Simple Lifting Machines

​Velocity Ratio (V.R)

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​The ratio of s_E to s_L is called the velocity ratio:

​As V.R is a ratio of two distances, it is a dimensionless quantity which means it has no units

Multiple Choice

Example Problem - Part 2/3

The lifting machine raises the crate through a distance of 1.6 m and the effort moves through a distance of 16 m. Calculate the velocity ratio of the machine.

• 15

• 10

• 6

• 1

​Parameters of Simple Lifting Machines

​Efficiency (η)

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​The ratio of M.A to V.R gives the efficiency of the machine:

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​

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Multiple Choice

Example Problem - Part 3/3

Calculate the efficiency of the lifting machine lifting the crate (use your answers from Part 1 and 2).

• 48.5%

• 58.5%

• 68.5%

• 78.5%

​Parameters of Simple Lifting Machines

Summary:

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Multiple Select

Question 1 - Part 1/3

A simple lifting machine raises a load of 825 N through a distance of 0.3 m. The effort is 250 N and moves through a distance of 3.3 m.

First determine the mechanical advantage of this machine:

• 2.1

• 3.3

• 4.5

Multiple Choice

Question 1 - Part 2/3

A simple lifting machine raises a load of 825 N through a distance of 0.3 m. The effort is 250 N and moves through a distance of 3.3 m.

Now determine the velocity ratio of the machine:

• 10

• 11

• 12

Multiple Choice

Question 1 - Part 3/3

A simple lifting machine raises a load of 825 N through a distance of 0.3 m. The effort is 250 N and moves through a distance of 3.3 m.

Finally, determine the efficiency of this machine:

• 30%

• 60%

• 90%

Multiple Choice

Question 2

A simple lifting machine has a velocity ratio of 8. If the efficiency of the machine is 30% when the load is 580 N, calculate the effort required.

• 168 N

• 186 N

• 205 N

• 242 N

Multiple Choice

Question 3

The efficiency of a simple lifting machine is 50%. If a load of 1.2 kN is raised by an effort of 300 N, determine the velocity ratio

• 6

• 8

• 10

• 12