Chapter 12: Simple Machines

Introduction: Simple Machines

In this chapter, you will learn about the different applications of simple machines and how they make work easier. Humans always use a number of tools or devices to carry out different activities which include; lifting objects, splitting fire wood, cutting materials among others. These tools are referred to as simple machines.
They basically enable you do more work with less effort by both multiplying and changing the direction of the applied force.

12.1 Simple Machines
Suppose that you are required to carry out the activities shown in Figure 12.1.
Imagine how difficult it would be to carry out the same work without such simple machines in place.

In this section, you will basically identify the various types of simple machines and state practical applications.
Activity 12.1: Identifying types of simple machines
What you need: metre rule, fixed support and G-clamp, notebooks, braille paper, stylus, slate, Perkins brailler,
You have been provided with the various types of simple machines as shown in Figure 12.1.
What to do;
In groups

1. Identity and name each of the simple machine. A, B, C, D, E and F.
2. Suggest some practical applications for each component identified above.

Humans have invented basically six devices that combine to make work much easier than it would be with out them. These are called simple machines and include; the wedge, wheel and axle, pulley, screw, lever, and an inclined plane.
Simple machines work by changing the direction of a force or the amount of a force needed to perform a given task. They allow small effort to move large load as well as a small movement of the effort to produce a large movement in the load.
The main objective of you learning about simple machines is being in position to clearly classify them basing on how much each machine simplifies a given task.
In this regard, you should read more about mechanical advantage, velocity ratio and the efficiency of a simple machine.
Activity 12.2: Understanding the key terms used in simple machines
What you need: Internet, and any other research material, notebooks, braille paper, stylus, slate, Perkins brailler
What to do:

1. In groups, discuss the meaning of mechanical advantage, velocity ratio and the efficiency of a machine.
2. What does it mean to say that a machine has a mechanical advantage:a) Greater than 1 b) Less than 1 c) Equal to 1
3. Jane applied an effort of 5 N to a machine so as to over come a load of 20 N. Determine the mechanical advantage of the machine.
4. The mechanical advantage of a pulley system in raising a flag is 6. If a girl applies a force of 10 N to the pulley to raise the flag, what is the mass of he flag.

12.2 The Operation of Simple Machines
Every simple machine is designed to perform a specific task in such a way that we apply a small force to do much work. In this section, you will understand the working of different components of simple machines.
The Lever System
A lever is a rigid bar pivoted at a point called the fulcrum. In this case, a small force is applied over a long distance and then converted into a larger force over a short distance. Let us do Activity 12.3 to demonstrate how simple levers simplify work.
Activity 12.3: Demonstrating the working of simple levers
What you need:
Spring balance, nail, retort stand, meter rule,500 g mass, notebooks, braille paper, stylus, slate, Perkins brailler.
What to do; In groups

I. Use a nail to make 8 equally spaced holes on the metre rule in an interval of 10 cm.
2.Clamp a meter rule horizontally through the third hole as shown in Figure 12.3. Suspend the 500 g mass and the spring balance through hole 1 and 8 respectively.
3.Pull the spring balance down wards and note the scale reading when the metre rule is horizontal. Calculate the weight and compare your answer.
4. Record the perpendicular distance from the spring to the pivot
6.Repeat the (3) and (6) with the spring balance suspended from hole 7, 6, 5, 4, 3 and 2.

Present your results in a suitable table as shown below or describe your results:

7. Comment about the variation of the perpendicular distance to the pivot with the spring scale reading.
   The force applied to lift an object is called the effort ,whereas the load is weight being acted on. A fulcrum is a point where the lever turns. It’s sometimes referred as a pivot. Levers are classified into three groups which include; the first, second a third class lever depending on the relative position of effort, load and the fulcrum

In the first class lever, the fulcrum is between the load and the effort, while the load is between the effort and the fulcrum in the second class lever. Finally, the effort is between the load and the fulcrum in third class lever as shown below:

Activity 12.4: Determining the mechanical advantage. velocity ratio and efficiency of a lever
What you need : Retort stand, metre rule with 8 holes in the interval of 10 cm, 500 g mass, spring balance, and thread, notebooks, braille paper, stylus, slate, Perkins brailler.
What to do:

1. By considering the arrangement in Activityl 2.3, obtain different spring scale recording for different distances from the pivot to the spring balance.
2. Determine the mechanical advantage and velocity ratio for each recording
   and hence the efficiency of a lever.
3. Suggest some possible reasons as to why its efficiency is not 100%.
4. How can you improve the efficiency of the machine.
   By considering a first class lever below: The general principle behind any kind of a lever system is given as below.

Exercise 12.2

1. A lever system has a mechanical advantage of 1.5. If the load of 170 N is raised through a distance of 10 m by applying effort which moves through a distance of 20 m. Calculate the;
   a) Velocity ratio of the lever system.
   b) Effort applied to overcome the load.
   c) Calculate the efficiency of the machine.
   The Pulley System
   As previously discussed, simple machines always make our work easier. Suppose you are provided with a pulley that is to say; a wheel with a grooved rim, how can you show that this pulley actually simplifies work? In Activity 12.5, you will demonstrate how pulleys simplify work.
   Activity 12.5: Demonstrating the working of a pulley

What you need: spring balance, two retort stand, pulley, thread, 500 g mass, notebooks, braille paper, stylus, slate, Perkins brailler.
What to do;
In groups:

1. Use a spring balance to determine the weight of the 500 g mass in air.
2. Hang the mass on one end and the spring balance at the other end as shown in Figure 12.5.
3. Pull the spring balance downwards and note the spring scale reading at a point when the
   mass is just lifted above the ground.
4. Compare the scale reading in (3) to the weight of the mass and conclude about the
   weight or force in both cases.
5. List down some applications of pulleys.

The more the number of pulleys, the much easier it becomes to perform work using a pulley. That is to say; three pulleys make work much easier than one pulley.
In addition, pulleys can be classified as fixed or movable pulleys. Movable pulleys make work much easier and these are free to move up and down unlike the fixed pulleys such as a flag pole. In situations where the two types are combined, we have a bbck and tackle pulley as shown in Figure 12.6.

Exercise 12.3

1. A pulley system has a velocity ratio of 4. In this system, an effort of 65 N would just raise a load of 217 N. Find the efficiency of this system.
2. A single fixed pulley is used to draw water from an underground well at a school farm. An effort of 500 N used to draw water moves a distance of 6. O m to draw 650 N of water through a height 2.0 m.
   (a) What is the mechanical advantage of the system?
   (b) Find the velocity ratio of the system.
   (c) Determine the efficiency of the system.
3. A crane lifts a load of 940 N when an effort of 116 N is applied The efficiency of the crane is 75 %. Calculate the:
   (b) Velocity ratio
   (a) Mechanical advantage
   The Inclined Plane
   It is practically easier to lift a heavy load up a ramp than just vertically upwards.
   This takes a longer period of time to reach a desired height but far much easier.
   Let us do Activity 12.6 to demonstrate how a slope simplifies work by allowing the load to be gradually raised.

Activity 12.6: Demonstratinq the workinq of an inclined plane
What you need: table, piece of wood, Spring balance, 500 g mass,notebooks, braille paper, stylus, slate, Perkins brailler
What to do;

1. Use a spring balance to lift the wooden block vertically above the top of a table. Record the reading on the spring balance.
2. Arrange the piece of wood in such a way that it forms an incline as shown in Figure 12.7.
3. Attach the mass to the spring balance and pull it up the incline.
4. Record the reading on the spring balance.
5. Compare the value in (4) to the weight of the body.
6. What do you think will happen to the spring reading if the plane is made longer in terms of length?
7. Suggest situations in real life where you Figure. 12.7: The of an I can apply this simple machine.
8. Suggest possible ways of how you can increase the efficiency of an inclined plane.

When the inclined plane is perfectly smooth then the work done by load is equal to the work done by effort. This can be illustrated as below:
Load x height of the plane = Effort x length of the plane

Exercise 12.4

1. A wheel barrow canying load of 400N is pushed through an incline of length 15 cm and height 5 cm. Calculate the;
   a) Velocity ratio of the simple machine.
   b) The mechanical advantage of the incline if the effort applied is 150 N.
   c) Efficiency of the machine.
   d) Work output
   e) Work input
   The Gear System
   Gears have teeth which inter lock directly with one another to facilitate motion.
   They are used to transmit rotational motion from one shaft to another. When gears with different sizes are meshed together, the smaller gear is called the driving gear while the larger is the driven gear.

Activity 12.7: Demonstrating the working of a gear
What you need: Two container tops with grooves and different diameters, Wooden sheet, and two nails, notebooks, braille paper, stylus, slate, Perkins brailler.
What to do:
1.Locate the center of each container top and use a nail to fix the tops on a wooden sheet in such a way that the grooves fit into each other.
2. Steadily turn the top A through one complete revolution and note how many revolutions the top B makes.
3.Repeat (2) but this time rotating container top B.
4.Compare the number of revolutions performed by the driven container top in each case.
5 .Suggest a relationship between the number of teeth and speed of rotation

The wedge
You have probably ever used tools like pangas, axes, knives among others to cut various kinds of material.
These are wedges and can be made of metal, wood or any other material.
They need to just have a sharp end with a triangular shape in general.
It has a number of applications as shown in Figure 12.10.

Activity 12.8: Understanding the working of a wedge
What you need: Notebooks, braille paper, stylus, slate, Perkins brailler.
What to do:
Required is to split a piece of wood using a wedge shown in the figure below.

1. In your respective groups, consider the diagram and discuss how wedges simplify work.
2. In your respective groups, identify some other practical applications of a wedge as a simple
   machine. Include diagrams in your work and make a presentation to the rest of the class members.
3. Suggest waysofhowonecan improve on the efficiency of operation of a wedge.

Other types of simple machines include wheel and axle, and screw. A screw consists of an inclined plane wrapped around the central cylinder. It converts rotational motion into linear motion. They move objects to greater depths and are commonly used to keep components together. The wheel and axle is the
most common simple machine used by humans to simplify work. Such devices include; steering wheel, door knob, among others.

Exercise 12.5

1. Discuss how you can determine the mechanical advantage and the velocity ratio of a screw and the wheel and axle.
2. Identify real life scenarios where the screw principle is applied.
   3.A machine whose velocity ratio is 8 is used to lift a load of 300 N. The effort required is 60 N.
   (a)Calculate the mechanical advantage of the machine.
   (b)Calculate the efficiency of the machine.
   (4)A machine ofefficiency 75 % lifts a man of 90 kg through a vertical distance of 3 m. Find the work required to operate the machine.
   (5)A machine requires 6000 J of energy to lift a mass of 55 kg through a vertical distance of 8 m. Calculate its efficiency.
   (6)A worker uses a crow bar 2.0 m long to lift a block ot weight 750 N.

Calculate the position of the pivot in order to apply an effort of 250 N.
Find the: (i) Mechanical advantage
(ii) Velocity ratio