WBBSE Notes For Class 6 School Science Chapter 9 Common Machines

Chapter 9 Common Machines Introduction To Machines

To do anything at all to lift a box, to push a car, to get out of bed, to jump in the air, to brush your teeth you need to use a pushing or pulling action called a force.

If you go around telling people you are strong, what you really mean is that your body can apply a lot of force.

You may have watched incredibly strong people on TV pulling trucks or trains with their bare hands, but there’s a limit to what even the most muscle-bound human body can do.

Machines let us go beyond that limit. Machines can make us all strong.

When you hear the word “machine”, you probably think of something like a bulldozer or a steam locomotive.

But in science, a machine is anything that makes a force bigger. So a hammer is a machine. A knife and a fork are machines. And even a spoon is a machine.

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Think about your home. There are probably all sorts of machines in every room. Which room has the most machines? Your kitchen is likely to be the most probable answer.

The large machines are usually the most noticeable-the refrigerator, the oven, the microwave, and perhaps the dishwasher.

They make keeping food fresh, preparing food, cooking, and cleaning much easier. Things such as knives, taps, can openers, doors, tongs, and bottle openers are all examples of machines that help to make our lives easier.

Other machines in the home that are useful and make our life easier include the washing machine, vacuum cleaner, and sewing machine.

Coming to a place outside the home you can see all types of machines at work automobiles, trucks, cranes, cement mixers, bulldozers, mechanical diggers, drilling machines, and all sorts of power tools.

These machines use lots of energy, but they are able to do lots of work that humans can not manage with just muscle power.

Perhaps the first example of a human-made machine designed to manage power is the hand axe made by chipping flint or stone to form a wedge.

These were used in butchering hunted animals, digging, chopping wood and removing tree bark, etc.

 

WBBSE Solutions for class 6 school science chapter 9 common machines flint or stone

WBBSE Solutions for class 6 school science chapter 9 common machines hand axe

Definition of a machine :

A machine is a tool containing one or more parts that use energy and change the amount, speed, or direction of a force to perform an intended action.

Machines are nowadays often motorized. Historically, it required moving parts to classify as a machine.

However, the advent of electronics has led to the development of devices without moving parts that are considered machines.

Chapter 9 Common Machines Utilities Of Machine

We cited quite a few examples of machines in the previous section. All these machines have one thing in common when you apply a force to them, they increase their size and apply a greater force somewhere else.

You can’t cut meat with your hand alone, but if you push down on a knife, the long handle and the sharpened blade magnify the force you apply with your hand, and the meat slices effortlessly.

When you pound a nail with a hammer, the handle increases the force you apply.

And because the head of the hammer is bigger than the head of the nail, the force you apply is exerted over a smaller area with much greater pressure and the nail easily enters the wood.

Try pushing in a nail with your finger and you’ll appreciate the advantage a hammer gives you.

Living in a world without machines is now almost impossible to imagine. Without even the simplest machines, many tasks that we do every day would be almost impossible.

Machines make it easier for humans to perform everything from the simplest to the most complicated of tasks.

A washing machine, for instance, saves a lot of time as we can do other things while the clothes are being washed.

Vacuum cleaners save a lot of time and energy in cleaning the floors or carpets. A sewing machine is also a very useful machine. Sewing by hand is a very slow job requiring a lot of patience.

Using a sewing machine helps to stitch clothes quickly and neatly. Let us now learn about the advantages of the use of machines.

The following are the advantages of the use of machines :

1. Use of natural forces:

Machines have made it possible to harness the forces of nature in

Simple machine:

in earlier times when a human being needed to move something heavy, he or she probably picked up a long stick, stuck it under the edge of the heavy object and stuck it under the edge of the heavy object, and then pushed it down on the other end of the stick.

The service of man. Man can fly in airplanes, he can connect continents in seconds, and electricity can be generated from sunrays, waterfalls, winds, etc. All these have been made possible with the aid of machines.

2. Heavy and delicate work made simple :

Tasks that are too heavy or too delicate for human muscles to do can be done easily by a machine. A crane can lift loads beyond the human capacity. Without the aid of machines, such jobs would not have been done.

3. Faster and more accurate work :

Only machines are capable of mass production, that too accurately, without a break and for a continuous duration.

While man can make only a few articles in a day by himself, machines employed in factories can make thousands per day for years together with extreme accuracy.

A human being, for example, can not paint exactly the same picture twice. But a machine can turn out thousands of identical articles. This has also resulted in the availability of durable articles at a much cheaper price.

4. More employment:

The introduction of machines in the modern society has created many new occupations. It has thus widened the scope of employment.

5. Hazardous work environment:

Human beings are relieved of all disagreeable and unpleasant jobs in hazardous environments by suitably deploying machines to do the same.

However, it must be remembered that machines are also associated with certain evils. These may be loss of human skill, over-dependence, monotony, destruction, and so on.

WBBSE Solutions for class 6 school science chapter 9 common machines hazardous work environment

Chapter 9 Common Machines Types Of Machine

Machines can be simple or complex.

Simple machine:

In earlier times when a human being needed to move something heavy, he or she probably picked up a long stick, stuck it under the edge of the heavy object, and then pushed it down on the other end of the stick.

Thus the first simple machine was invented. The simplest form of using one thing to accomplish something faster or better. They were the first ones created and we still use them today.

Definition of a simple machine:

A simple machine is a device that simply transforms the direction or magnitude of a force. It has fewer parts and uses human force to work.

Simple machines help us to do our work faster by either increasing or decreasing the force that we apply.

It may change the direction of the applied force also. Keep in mind that the ratio of the output obtained from a simple machine to the applied force is called the mechanical advantage.

There are 6 basic simple machines:

The lever, the wheel and axle, the inclined plane, the wedge, the pulley, and the screw.

Several of these simple machines are related to each other as shown below Wheel and axle and pulley are modifications of the lever whereas the wedge and screw are modifications of the inclined plane.

The idea of a simple machine originated with the Greek philosopher Archimedes around the 3rd century BC, who studied the Archimedean simple machines lever, pulley, and screw.

WBBSE Solutions for school science class 6 chapter 9 common machines simple machine

Complex machine:

Simple machines can be regarded as the elementary “building block” of which all more complex machines (sometimes also called “compound machines”) are composed.

Thus complex machines have two or more simple machines working together.

Many of our everyday tools and the objects we use are really complex machines. Let us take a few examples to get the idea clear. Scissors are a good example.

The edge of the blades is wedged. But the blades are combined with a lever to make the two blades come together to cut.

The bicycle that you ride consists of wheels, levers, and pulleys all used in the mechanism of it to make it work.

WBBSE Solutions for school science class 6 chapter 9 common machines scissor

A lawnmower combines wedges (the blades) with a wheel and axle that spins the blades in a circle. But there is even more.

The engine that drives the lawnmower probably works in combination with several simple machines and the handle that you use to push the lawnmower around the lawn is a form of a lever.

So you see that even something complicated can be broken down into the simplest of machines. Other examples of complex machines include sewing machines, printing machines, computers, vehicles, etc.

Definition of a complex machine:

Complex machines have two or more simple machines working together.

Thus the mechanical advantage of a complex machine is just the product of the mechanical advantages of the simple machines of which it is composed.

Chapter 9 Common Machines Lever

Idea of Lever

Levers were probably the first machines used by human beings. It is a long tool such as a pole or a rod put under an object to lift it.

Levers are all around us. The handle of the spoon is a lever since it makes it easier for us to open the lid of a can. The lever becomes more efficient when combined with a fulcrum.

WBBSE Solutions for school science class 6 chapter 9 common machines idea of lever

The fulcrum is another object, maybe a rock, used to give alginate Lana to tone support or brace under the long tool. This gives the long pole something to push down against.

Let us take another example to get the matter clear. When you sit on a see-saw, you have probably found out that you need to sit further from the balance point if the person at the opposite end is heavier than you.

The balance or pivot point acts as the fulcrum here. The further away from the fulcrum you sit, the more you can multiply the force of your weight.

If you sit a long way from the fulcrum, you can even easily lift a much heavier person sitting at the other end provided of course they sit very close to the fulcrum on their side.

The force you apply with your weight is called the effort. The fulcrum produces a bigger force to lift the load (here it is the weight of the other person).

The words “effort” and “load” are associated with the working of the lever. However, the important thing fo to remember about levers is that the force you produce (which drives the load) is bigger than the force you apply as effort.

Some examples of levers are:

Door handles the claws of a hammer (for removing nails), light switches, bottle openers, tongs, knives, screwdrivers, wrenches, scissors, and hinges.

 

WBBSE Solutions for school science class 6 chapter 9 common machines effort and load

WBBSE Solutions for class 6 school science chapter 9 common machines door handles

The force that is used on the lever is called the effort (E).

The weight that is moved or lifted by the lever is called the load (L).

The point on the lever that does not move while the lever does the work is called the fulcrum (F). Hence it acts as a fixed point of support for the lever.

The arm that extends from the fulcrum to the point of application of the effort is called the effort arm. In the same way, the arm that extends from the fulcrum to the load point is called the load arm.

The location of the fulcrum helps to determine how well the lever will perform work.

The closer the fulcrum is to the load being lifted (meaning a shorter load arm compared to the effort arm), the higher shall be the load that the person can lift.

The longer the lever, the easier shall be on the part of the person to put effort to lift the load. Thus with a long lever, you can exert a lot of leverage.

 

WBBSE Solutions for school science class 6 chapter 9 common machines removing nails

 

WBBSE Solutions for school science class 6 chapter 9 common machines lever

When you use The fulcrum is another object, maybe a rock, used to give alginate Lana to tone support or brace under the long tool. This gives the long pole something to push down against.

Let us take another example to get the matter clear. When you sit on a see-saw, you have probably found out that you need to sit further from the balance point if the person at the opposite end is heavier than you.

The balance or pivot point acts as the fulcrum here. The further away from the fulcrum you sit, the more you can multiply the force of your weight.

If you sit a long way from the fulcrum, you can even easily lift a much heavier person sitting at the other end provided of course they sit very close to the fulcrum on their side.

The force you apply with your weight is called the effort. The fulcrum produces a bigger force to lift the load (here it is the weight of the other person).

The words “effort” and “load” are associated with the working of the lever.

However, the important thing fo to remember about levers is that the force you produce (which drives the load) is bigger than the force you apply as effort.

Some examples of levers are:

Door handles, the claws of a hammer, light switches, bottle openers, tongs, knives, screwdrivers, wrenches, scissors, and hinges.

The force that is used on the lever is called the effort (E).

The weight that is moved or lifted by the lever is called the load (L).

The point on the lever that does not move while the lever does the work is called the fulcrum (F). Hence it acts as a fixed point of support for the lever.

The arm that extends from the fulcrum to the point of application of the effort is called the effort arm. In the same way, the arm that extends from the fulcrum to the load point is called the load arm.

The location of the fulcrum helps to determine how well the lever will perform work.

The closer the fulcrum is to the load being lifted (meaning a shorter load arm compared to the effort arm), the higher shall be the load that the person can lift.

The longer the lever, the easier shall be on the part of the person to put effort to lift the load. Thus with a long lever, you can exert a lot of leverage.

When you use an axe or a wrench, the long handle helps to magnify the force you can apply. The longer the handle, the more leverage you get.

So a long-handled wrench is always easier to use than a short-handled one. And if you can’t budge a nut or bolt with a short wrench, try one with a longer handle.

Hence it can be easily understood that it’s really all in the distance between the effort, the fulcrum, and the load upon which the actions of the lever vary.

Take the case of a spoon. The point at which the spoon touches the outer edge of the can is the fulcrum (F).

Here the load arm is very small, just extending from the fulcrum to the end of the spoon handle that touches the inner edge of the lid.

The effort arm is the longest, which is extended from the fulcrum to the spoon head.

WBBSE Solutions for school science class 6 chapter 9 common machines the case of a spoon 1

WBBSE Solutions for school science class 6 chapter 9 common machines the case of a spoon 2

Chapter 9 Common Machines Classes of Lever

All levers give leverage, but not all of them work the same way. There are actually three different kinds of levers (sometimes known as classes).

The class of a lever depends on the relative positions of the efforts, load, and fulcrum.

First-class or Class-1 levers

In a First class lever, the effort or force we apply is on the opposite side of the fulcrum to the force the lever produces.

Hence the fulcrum is placed between the effort and the load. See-saw, beam balance, and scissors are all first-class levers.

Hence the load is placed between the fulcrum and the effort. Nutcrackers, bottle openers,s, and wheelbarrows are all examples of Second class levers.

 

WBBSE Solutions for school science class 6 chapter 9 common machines first class levers

 

WBBSE Solutions for school science class 6 chapter 9 common machines scissor 2

Second-class or Class-2 levers

A Second class lever is arranged in a different way, with the fulcrum at one end. The effort or force is applied at the other end and the force is produced in the middle of the level.

 

WBBSE Solutions for class 6 school science chapter 9 common machines a second class lever

 

WBBSE Solutions for school science class 6 chapter 9 common machines wheel barrows

Third-class or Class-3 levers

A Third class lever, like a Second class lever, has the fulcrum at one end.

But the two forces switch around. Hence the effort or force is applied at the middle and the force is produced at the opposite end. Thus the effort is placed between the fulcrum and the load.

Third Class levers reduce the force you apply, giving you much greater control. Stapler, fishing
rod and tongs are examples of Third Yowlega pro-class levers.

 

WBBSE Solutions for school science class 6 chapter 9 common machines third class lever

 

WBBSE Solutions for school science class 6 chapter 9 common machines road and tongs

Chapter 9 Common Machines Mechanical Advantages of Various Classes of Lever

Machines are usually designed so that a small effort may overcome a large load. This makes the work easier to be done by the machine.

The advantage that we get from the machine is called its mechanical advantage.

It is a number that expresses the relationship between the load overcome by the machine and the effort applied to the machine.

First-class levers

Here the fulcrum is nearer to the B-end, the B effort (P) is applied at the end A, and the load
(W) is at the end of B.

Since AC (effort arm) is longer than BC (the load arm), W will be greater than P. This means that a big load may be raised by a small effort.

So, the lever of the first class has sufficient mechanical advantage. But depending on the position of the fulcrum C, the mechanical advantage of the lever may be equal to 1.

For example, in a common balance, the fulcrum is exactly at the midpoint of the balance beam which makes the length of the effort arm equal to that of the load arm.

Hence the mechanical advantage of a common balance is equal to 1.

Mechanical advantage \(\text { Mechanical advantage }=\frac{\text { Load }(W)}{\text { Effort or force }(P)}=\frac{\text { Effort arm }}{\text { Load arm }}\)

Second class levers

Here the fulcrum C is situated at one end of the rod, the effort P is at the other end and the load W is applied in between them but nearer to the fulcrum C.

WBBSE Solutions for school science class 6 chapter 9 common machines a and b load at the end

 

WBBSE Solutions for school science class 6 chapter 9 common machines common balance

 

WBBSE Solutions for school science class 6 chapter 9 common machines second class levers

The mechanical advantage =\(\frac{W}{P}\)=\(\frac{AC}{BC}\)

Since the arm AC (effort arm) is always longer than the arm BC (load arm), the load will be always greater than the effort.

In other words, in the lever of the second class, a small effort will always overcome a heavy load. The lever has, therefore, a mechanical advantage always greater than 1.

Third class levers

A third-class lever does not have the mechanical advantage of either the first or the second-class levers and so, examples are less common.

Here the fulcrum C is situated at one end of the rod, the load W is applied at the other end and then but nearer to the load.

The mechanical advantage =\(\frac{W}{P}\)=\(\frac{AC}{BC}\)

Since AC (effort arm) is always smaller than BC (load arm), the load will be always smaller than the effort. In other words, a small load is overcome by a greater effort.

For this reason, this lever has no mechanical advantage. Sometimes it may so happen that the load cannot be lifted directly by applying a force nor is it convenient to use the levers of the first two classes.

In such cases, the third-class lever is used al- although it has no mechanical advantage.

These levers are good for grabbing something small, fiddly, or dirty or picking up something that could be squashed or broken if too much pressure is applied.

Hence, the human arm is an example of the lever of the third class.

WBBSE Solutions for class 6 school science chapter 9 common machines a third class levers

Chapter 9 Common Machines Concept of an Inclined Plane

The inclined plane is simply a ramp whose one end is higher than the opposite end. This allows things to go from a low place to a higher place without much effort.

But the load has to be moved over a longer distance as compared to pulling it up vertically. Whether the inclined plane is long or short, the amount of work done shall be the same.

Thus an inclined plane does not decrease work but makes it easier. On the other hand, gravity makes it easier to move an object down a ramp than up that ramp.

A slide in the children’s park, a d-leaning ladder, a staircase, and a sloping wooden plank are examples of inclined planes.

The acute angle that the inclined plane makes with the ground is called the angle of incline or slope.

If the slope of the inclined plane is low meaning that a smaller angle between the ground and the plane, then it is easier to climb up.

The mechanical advantage of an inclined. the plane is linked to the slope or angle of the incline.

WBBSE Solutions for school science class 6 chapter 9 common machines children park

WBBSE Solutions for school science class 6 chapter 9 common machines leaning ladder

 

WBBSE Solutions for school science class 6 chapter 9 common machines sloping wooden plank

 

WBBSE Solutions for school science class 6 chapter 9 common machines angle of incline

The mechanical advantage=\(\frac{\text { Length }}{\text { Height }}\)

It is apparent that the length of the inclined plane is greater than its height. Hence, by applying a small effort, the big load may be raised. The inclined plane has a mechanical advantage always greater than 1.

Uses of the inclined plane

  1.  As loading ramps to load and unload goods on trucks, ships, planes, etc. FEAR
  2. As wheelchair ramps for aged, invalid persons and patients.
  3.  As staircase and escalators.
  4. As conveyor belts.

Chapter 9 Common Machines Wheel And Axle, Wedge, Pulley, Screw

The Wheel and Axle

The wheel has always been considered a major invention in the Wheel history of mankind. But it really would not work till it is attached to the axle.

An axle is a rod or a pole centered in the wheel that allows the wheel to turn around it.

The wheel then spins in a balanced circle to be used for transportation as in a car or bike or to turn the hands of a clock.

Wheels are found where things turn in a circle such as an electric fan, a motor, a merry-go-round, etc.

Both of wheel and axle can rotate freely together about a fixed axis that passes through their common center. This axis is called the axis of rotation.

In recent days we see wheels also under the legs of computer tables, office chairs, traveling bags, and shopping trolleys.

WBBSE Solutions for school science class 6 chapter 9 common machines weel and axle

Wheel and axle arrangement can be put to use in lifting loads. How much load the effort can lift, depends on how many times the wheel is larger than the axle.

WBBSE Solutions for school science class 6 chapter 9 common machines wheel

If the diameter of the wheel is twice that of the axle, then, a certain effort given to the axle shall lead to the wheel, being twice as large as the axle, capable of lifting a load twice as heavy.

The mechanical advantage of wheel and axle is defined as.

Mechanical advantage =\(\text { mechanical advantage }=\frac{\text { Radius of the wheel }}{\text { Radius of the axle }}\)

Chapter 9 Common Machines The Wedge

The wedge might appear to be just an inclined plane, but it is actually two inclined planes that meet at a sharp edge. The use of a wedge is actually different in nature.

The wedge is used to separate an object apart. This is needed to cut, tear, or break something in two. A wedge can also be used to keep things together or secure things from movement.

 

WBBSE Solutions for school science class 6 chapter 9 common machines wheel and axle resistance

Some examples of wedges that are used for separating might be a shovel, a knife, an axe, a pick axe, a saw, a needle, scissors, or an ice pick.

But wedges can also hold things together as in the case of a staple, push pins, tack, nail, doorstop, or a shim.

 

WBBSE Solutions for school science class 6 chapter 9 common machines wedge

Chapter 9 Common Machines The Pulley

The pulley is actually a modified version of a wheel and axle that is combined with a rope, chain or other cord passing through a groove to allow moving something up and down or back and forth.

The rod that passes through the center of the pulley is called the axle. The pulley rotates freely about the axle.

The pulley can be combined with other pulleys to reduce the amount of work necessary to lift huge amounts of weight or to lower them down.

 

WBBSE Solutions for school science class 6 chapter 9 common machines break something

It can also make moving something such as a flag up the pole convenient to do from the ground. It changes the direction of the applied force necessary to do the work.

You pull down on the rope, but the flag goes up. Pulleys are used in window blinds and drapery to move them up and down or back and forth.

Pulleys are also used on ships to raise and lower sails, in the industry to raise and lower heavy cargo, or on cranes for use in moving construction equipment.

Elevators also use pulleys to move the car up and unban down from floor to floor.

There are three types of pulleys-fixed, movable, and compound. A fixed pulley is fastened to some support by means of a hook.

WBBSE Solutions for class 6 school science chapter 9 common machines the pulley

 

WBBSE Solutions for school science class 6 chapter 9 common machines center of the pulley called the axle

A very common use of a single fixed pulley is in lifting water from wells. A movable pulley is one that remains fastened to the load itself. This type of pulley is free to move up and down.

Examples of movable pulleys include construction cranes, modern elevators, and some types of weight-lifting machines at the gym.

The third type of pulley is the compound pulley, which consists of combinations of fixed and movable pulleys.

WBBSE Solutions for school science class 6 chapter 9 common machines a fixed pullry

 

WBBSE Solutions for class 6 school science chapter 9 common machines movable pully

 

WBBSE Solutions for school science class 6 chapter 9 common machines compound pulley

Chapter 9 Common Machines The Screw

Cut out a triangular piece of paper as shown in. This piece of paper resembles an inclined plane. Apply a deep color along the margin of the inclined plane ie., along the inclined side of the paper.

Now if you roll the paper along a pencil as shown, you would see that the darkened inclined margin of the paper would create spiral markings on the pencil’s body.

These spiral markings on the pencil’s body are similar to those on the body of a screw.

 

WBBSE Solutions for school science class 6 chapter 9 common machines darkened margin of inclined plane

 

WBBSE Solutions for school science class 6 chapter 9 common machines roll the paper along a pencil

 

WBBSE Solutions for school science class 6 chapter 9 common machines create spiral markings on the pencils body

The screw is thus a twisted inclined plane wrapped around a rod, cylinder, or pole. The sharp spiral ridges on the body of the screw actually make an inclined plane.

It allows movement from a lower position to a higher position but at the same time, it moves in a circle. That makes it take up less horizontal space.

A screw can also act to hold things together in some cases due to the sharp ridges. Since the sharp ridges of a screw are spiral, they get driven easily inside wooden planks with the help of a screwdriver.

This is why carpenters prefer using screws to nails. Some examples of the uses of a screw are in a jar lid, a drill, a bolt, the cap of a light bulb, faucets, a car lifting jack, and bottle caps.

Circular stairways are also a form of a screw. Another use of the screw is in a device known as a screw pump.

WBBSE Solutions for school science class 6 chapter 9 common machines body of a screw

A huge screw shape is lowered into the water and by turning the screw the water is moved up the twisted shaft and lifted to where it is needed.

Screw pumps are often used in agricultural settings such as farms and for irrigation. When a screw is turned once round, it advances a distance equal to the space between its two neighboring threads.

This distance is known as the pitch of the screw. You will find that it is more difficult to drive a screw with a bigger pitch into a piece of wood than a screw with a smaller pitch.

WBBSE Solutions for school science class 6 chapter 9 common machines pitch of the screw

Chapter 9 Common Machines Maintenance Of Machines

Machines undergo wear and tear as they are put to use on a regular basis.

If not taken care of properly, this may lead to permanent damage to the component parts, discoloration or rusting, malfunctioning, decreased efficiency, and above all, serious danger to the person operating the machine.

Hence regular upkeep and maintenance on the overall functionality and condition of machines are a must to keep the continuity of what is expected and the standard performance of the machines.

Simple steps to follow for maintenance of machines :

1. Keep it routine:

Just like the annual check-up with a physician, a regular check-up has to be made to inspect the conditions of the parts of a machine in order to ensure desired performance it.

This is an absolute emergency for heavy and complex machines.

2. Cleaning:

Routine cleaning after every use increases the longevity and performance of a machine many times.

3. Lubrication:

Lubrication of moving parts using grease or oil is an important part of regular machine maintenance. The lubrication procedure may be repeated in line with the degree of usage.

4. Rust prevention:

Metallic parts of a machine shall be protected from rusting caused by moisture ingress by suitably applying an anti-rust synthetic enamel paint or oil paint.

5. Don’t overwork the machine:

It is always advisable that the stated performance of a machine should not be exceeded at any point in time.

Overwork leads to greater wear and tear and finally to the shorter life span of the machine under consideration.

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