Home PRIMARY Topic 5 – Complex Machines – Science and Technology Grade Seven (VII)

Topic 5 – Complex Machines – Science and Technology Grade Seven (VII)

25
0
Topic 5 - Complex Machines - Science and Technology Grade Seven (VII)

Topic 5 – Complex Machines – Science and Technology Grade Seven (VII)

Topic 5 – Complex Machines – Science and Technology Grade Seven (VII):- Complex machines science and technology grade seven vii questions and answers pdf, Complex machines science and technology grade seven vii questions and answers, Complex machines science and technology grade seven vii pdf free download

Complex machines science and technology grade seven vii pdf, Complex machines science and technology grade seven vii notes, Complex machines science and technology grade seven vii answers, science and technology standard 7 by tie, standard 7 books pdf

Structure of complex machines

Think: Importance of complex machines in daily uses

Complex machines are made up of two or more simple machines. These machines simplify work by reducing the amount of force applied and by changing the direction of the force applied.

Therefore, two or more simple machines which form a complex machine are designed to work together. Examples of complex machines are mortise locks, sewing machines, bicycles, grain milling machines, and juice making machines.

Mortise lock

The mortise lock is an example of a complex machine, with a key to lock and unlock the door. The mortise lock is a complex machine because it is made up of two or more simple machines. There are different types of mortise locks depending on the need. All mortise locks function similarly.

The structure of the mortise lock

The mortise lock is made up of two main parts: the outer part and the inner part. The outer part is made up of a lock handle and a box that covers the lock. The inner part, shown in Figure 1, is made up of simple machines.

Those machines are levers, the latch spring, latch bolt and deadbolt. These machines work together during locking and unlocking the door using the key.

How the mortise lock works

The mortise lock has two parts to lock and unlock the door. The first part is the one with the handle to hold when closing and opening the door. This part is made up of the latch spring and latch bolt.

As you turn the handle down, the latch spring pulls the latch bolt into the lock and lets the door open. The second part is the one that locks and unlocks the door using the key. This part works using a lever system and deadbolt. Each mortise lock is unlocked using a specific key.

The key has teeth that correspond to a specific lock. The levers prevent the deadbolt from moving. When you insert the key and rotate it, the lever moves and releases space. The space allows the deadbolt to enter or exit the socket on the door casing.

The number of levers in a mortise lock is commonly two, three, or five. However, there are mortise locks having one lever. The security of the mortise lock depends on the number of levers consisting the lock.

For example, a mortise lock made of five levers provides more security than the one made of two or three levers. It is easier to duplicate keys for a mortise lock made of one lever or two levers than for a lock made of three or five levers.

Sewing machine

A sewing machine is used to sew various items such as clothes, shoes, handbags, canvas, and belts. The sewing machine is a complex machine because it is made up of two or more simple machines.

There are different types of sewing machines depending on their uses and the sources of energy used by the machine. Some sewing machines are run by feet and others by hand. Other sewing machines use electric energy.

Despite their differences, these machines have almost similar structures. In this subsection, you will learn about the treadle sewing machine, which is run by feet.

How the treadle sewing machine works

When the feet work the treadle, a mechanical force that rotates the pulley system is produced. The pulley system consists of two wheels, which are a band wheel and a hand wheel. Both wheels are rotated using a belt. When the hand wheel rotates, it rotates the axle, causing the needle to drop and rise repeatedly.

The sewing machine uses two separate threads: one fed from above by the needle and the other fed from below by the bobbin mounted on a shuttle. The needle pushes the thread down through the material, catches the bobbin thread, and pulls it back up through the material.

Bicycle

A bicycle is a means of transport or exercise. Bicycles can also be used to carry luggage. The bicycle is a complex machine because it is made up of two or more simple machines. These machines work together to enable the bicycle move.

There are different types of bicycles. Some bicycles are operated by feet, and others are operated by fuel or electric motor. In this section, you will learn about a bicycle that is operated by feet.

The structure of a bicycle

A bicycle is made up of three types of simple machines. These machines are levers, pulleys, and the wheel and axle. The wheel and axle are at the front and back wheels. The second machine is the pulley.

The pulley consists of a chain that connects a large gear wheel with pedals and a small gear wheel mounted at the back wheel. The third type is a lever that is made up of two pedals as well as the bicycle brake as shown in Figure 3.

How the bicycle works

When the pedal is rotated, it sends a force to the pulley. The pedal rotates the large gear wheel. This wheel is connected to the small gear wheel by a chain.

As the chain moves, it drives the small gear wheel. When the small gear wheel rotates, it rotates the back wheel of the bicycle. This condition, in turn, moves the bicycle forward.

Handling a bicycle

The bicycle will last longer and work effectively if it is regularly inspected and repaired. In addition, cleanliness should be maintained. The bicycle must be washed with soap and water whenever it gets dirty.

The bicycle has rotating parts that rub each other. Therefore, it is important to lubricate such parts. Lubricants reduce friction, rust and corrosion of the moving parts. Lubricants are applied to the chain, wheel and axles, and pedals.

Lubricants are also applied to the inside of the wheel and axles system since they contain ball bearings. Ball bearings need to be lubricated to avoid eroding when the bicycle is moving. In addition, make sure that the brakes are working properly to reduce the risk of an accident.

Grain milling machine

Various grains are ground to get flour. This work is done by a grain milling machine. This machine is one of the complex machines. The grain milling machine is made up of two or more simple machines.

The structure of a grain milling machine

The grain milling machine is made of an inclined plane called hopper for putting grains, a mill, and a flour outlet. Three types of simple machines compose a grain milling machine.

These simple machines are the inclined plane, where grains are poured; the wheel and axle; and the pulley. A mill is made of a wheel and an axle. The wheel and axle are rotated by a pulley.

This pulley is made of a wide belt fastened in two wheels. The large wheel is connected to the motor or engine and the small wheel is connected to the mill as shown in Figure 4.

The grain milling machine can use fuel or electricity. A fuel engine machine converts fuel energy into mechanical energy. Similarly, an electrical motor machine converts electrical energy into mechanical energy.

How a grain milling machine works

When the machine is turned on, the motor or engine rotates the axle holding the large wheel. When the large wheel rotates, it causes the belt to rotate the small wheel, which is attached to the mill.

This enables the roller inside the mill to rotate rapidly and grind the grains. The mill is connected to a pipe that draws the flour from the mill. A special cloth is attached to the end of the pipe to prevent the flour from spreading.

Handling a grain milling machine

The grain milling machine consists of rotating parts. These parts rub each other and cause a rise in temperature. It is important to check the temperature of the machine so that it does not exceed the classified limit. If the temperature rises too much, turn off the machine.

Check the belt if it is properly tightened. If it is loose, tighten it so that the machine can work efficiently. Apply lubricants to all parts that rub each other. Lubricants should be changed at the appropriate time.

Make repairs as soon as you find a problem. This is a good strategy to make the machine last longer. The machine should also be cleaned regularly.

Juice making machine

There are various juice processing machines. Example are machines that grind or squeeze fruits such as a blender and fruit squeezer. The blender is a small machine used to make juice. Juice is a beverage produced from fruits, vegetables, or roots.

Fruits and vegetables are ground or squeezed, crushed, and filtered to obtain juice. The blender is one of complex machines. This machine consists of more than one simple machine.

The structure of the blender

The blender is made of a wheel and axle mounted on the motor. The motor is in the base of the machine and is covered to make it safe for use.

The motor converts electrical energy into mechanical energy. The axle is connected to blades. As the axle rotates, it rotates the blades like a fan. These parts of the blender are shown in Figure 5 (b).

Electric plug

(a) Juice machine (b) Parts of the juice machine
Figure 5: Structure of a juice making machine

How a blender works

When the blender is turned on, the motor rotates the axle. The rotating axle rotates the blades at high speed.

The blades grind fruits or vegetables and produce a thick liquid. Some water is added to the liquid. Then, the mixture is stirred and filtered to obtain juice.

Handling the blender

Caring for the blender depends on its type and specific instructions. The blender should be cleaned and stored in a safe place after use.

It is cleaned by wiping the base where there is a motor using a piece of cloth and soap. This part should not be immersed in water because water can damage the motor when it is turned on.

Other parts should be opened and washed with soap and water. The jug should be carefully cleaned since its blades are sharp.

This part can be cleaned with a soft cloth and rinsed with running water. Make sure the blades are dry before putting them back in place.

Topic 5 – Complex machines – Science and Technology Grade Seven (VII)

Topic 5 – Complex Machines – Science and Technology Grade Seven (VII)

Vocabulary

Blades – sharp knives mounted on a motor axle in a juice- making machine

Bobbin – a metal wheel wrapped with a sewing thread in a sewing machine

Treadle – a lever worked by the foot and imparting motion to a machine

CLICK HERE TO DOWNLOAD PDF FILE 

LEAVE A REPLY

Please enter your comment!
Please enter your name here