term 2 grade 7: technology worksheet - parkhurst primary

PARKHURST PRIMARY SCHOOL “Great oaks from little acorns will grow”

Term 2 Grade 7: Technology Worksheet Topic: Structures. (Notes)

1. Introduction. For thousands of years, people have been building structures to live in. The need for shelter is one of our basic needs. Structures are also built for many other purposes. There are two types of structures, namely natural and manmade. A manmade structure is one that has been made by humans, for example, a house. The structure of a house protects and contains the people and its contents.

Manmade structure – House

A natural structure is one that is found in nature, for example, a termite mound. The structure protects and contains the termites.

Natural structure – termite mound

2. Functions of structures

The functions of structures are to:

Protect – for example, a helmet.

Support – your skeleton supports your body and keeps it upright.

Contain – by surrounding a space so that what is inside is contained, for example, a tin can.

Span – a distance between two objects or places to connect them, for example, a bridge over a river, or a ladder.

Protect – Helmet Support – Skeleton

Contain – Tins Span – Bridge

A structure needs to be stable, so it does not fall over. It needs to be strong, so it does not break. It also needs to be rigid, so it does not bend easily. 3. Types of structures

The three main types of structures are shell, frame and solid structures. Shell Structure A shell structure gives protection from the outside and also acts as a container. A shell structure is very strong as the pressure is transferred to the outside of the structure. Try to press an egg between two fingers and you will see that it does not crack. Some shell structures are natural, for example, an eggshell, and some shell structures are manmade, for example, a box and a bottle.

Natural shell structure – Eggshell Manmade shell structure – Box

Frame Structure Frame structures give support. These structures are made up of different parts joined together to make a strong frame. A frame structure can be covered or open. Some frame structures are natural, for example, a skeleton, a cobweb and a leaf, and some are manmade, for example, an electricity pylon and a swing.

Natural frame structure – Leaf Manmade frame structure - swing

Solid Structure A solid structure only has one part with no spaces in-between. Solid structures are strong and can support a heavy load. Some solid structures are natural, for example, a rock, and some are manmade, for example, a brick.

Natural solid structure – rock Manmade solid structure – brick

4. Strengthening structures

There are always forces that are exerted on structures. These are either push (compression) or pull (tension) forces. Because of these forces, structures need to be strengthened, so they don’t fall over. Methods of strengthening structures include the following: Triangulation The triangle is the only polygon that does not change shape. When a force is exerted on it, the force spreads over all three sides of the triangle, so that it remains rigid and stable. This unique stability makes the triangle very useful in construction.

Triangulation is used in pylons Foundations Gravity and the heavy load of the structure push downwards, the ground pushes back up, and

air movements push from the side. A foundation spreads the load into the surrounding ground material and can help balance the wind force from the sides. The size of the foundation depends on the strength of the supporting ground. Many structures are built with strong foundations under the ground.

Foundations being built

Centre of Gravity The centre of gravity of an object is the average location of the weight of an object, where the weight is evenly spread, i.e., the point of the most downward force. The centre of gravity in a ball would be the centre of the ball, whilst the centre of gravity of a person would be higher than their waist, as there is more weight in the top half of the body than the bottom half. The most stable position is to have equal amounts of mass, and force, on each side of the centre of a structure. A structure with a central centre of gravity is more stable than one with its centre of gravity to one side.

Leaning tower of Pisa The stability (how well a structure stands) is affected by the size of the base of the structure. A structure with a large base is more stable than one with a smaller base. Taller structures should have wider bases. If the base or bottom of a structure is wider than the rest of the structure, then the structure will not easily fall over, because the centre of gravity will not move from the base. So when most of the weight of a structure is in its lowest point, it has a low centre of gravity and when most of the weight is higher up, it has a high centre of gravity. A structure with a low centre of gravity is more stable and this is why many structures are built with a strong, heavy base at the bottom.

Oil rig with low centre of gravity Reinforcing

Reinforcing is a technique used to make a structure stronger. Struts and beams are used for this purpose. In a frame structure, the parts of the structure are made up of various elements. Some structural elements can also help a structure to be stable.

Beams are used to withstand a load without bending.

Roof beams

A strut is an element of a structure that can resist a force pushing down on it, i.e., compression.

Struts between beams on bridges

A tie is another structural element that has a tensile force acting on it and therefore can resist a pulling force. Using cables that are fastened to the ground can help to prevent a structure from falling down.

Using cables on a bridge

A membrane is a structural element, which covers a structure, for example, your skin, or the canvas of a tent.

Ties and membranes used in a tent

5. Materials used in structures The strength of building materials depends on how they are used. Pleating, folding or

rolling paper can increase its stiffness. Building materials can be made in the same way.

Corrugated roofs are an example of pleating and pipes are an example of tubing. Tubing is used where stiffness and strength are required, as tubing can withstand compression (pushing force).

Corrugated roofing Pipes are an example of tubing

6. Cell phone towers as structures

A landline transmits what a caller is saying in one location to another person in a different location (or data when a fax is sent). The voices are transmitted via underground and surface cables with many joints and connections between the cables.

A cell phone transmits voices and data through radio waves to relay towers. A good signal and connection for communication depend on the distance to the nearest relay tower. Poor weather conditions can affect the signal quality.

Landline Cell phone Cell phone towers are found all over South Africa and most areas have cell phone coverage. In some places, towers can be found close together as they only have a short range. Cell phone towers are usually frame structures with pieces of metal welded and bolted together. A cell phone tower is an example of a frame structure. When it is built, it has to withstand weather conditions and not collapse.

A cell phone tower is a frame structure

Before designing any type of structure, there are many things to consider, like the purpose of the object or structure, the cost, and how it will affect the environment and people.

The environment is an important consideration as ‘visual pollution’ occurs when ugly structures are built that ruin the landscape.

These days, structures are often built to blend in with their surroundings or are camouflaged so they cannot be seen. Cell phone relay towers are often disguised as trees, for example.

Cell phone tower disguised as a palm tree


Term 2 Grade 7: Technology Worksheet Topic: Structures. (Exercises) Exercise 1: Purpose of structures. Complete the table below with one example for each category.

Purpose of structure Natural Man-made

1. To protect

2. To support

3. To contain/enclose

4. To span

Exercise 2: Natural or Manmade? Classify the objects below according to whether they are natural or manmade. Choose your answer by ticking in the correct column.

Picture Natural Manmade Picture Natural Manmade

1.

8.

2.

9.

3.

10.

4.

11.

5.

12.

6.

13.

7.

14.

Exercise 3: Shell, frame or solid? Classify the objects below according to whether they are shell, frame or solid structures. Choose your answer by ticking the correct column.

Picture Shell Frame Solid

Exercise 4: Examining structures. Look at the photos of different types of structures below and answer the questions that follow.

a. b.

c.

d. e.

1. Name each type of structure. a. _______________________ b. _______________________ c. _______________________ d. _______________________ e. _______________________

2. What type of structure are they?

__________________________________________________________________________

3. List three methods of strengthening that have been used on these structures. _____________________________ _____________________________ _____________________________

Exercise 5: Case study – Cell phone towers as structures. Look at the photos of cell phone towers below and answer the questions that follow.

a. b. c.

d. e. f.

g.

1. List methods of strengthening that have been used in these structures. Give examples. __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________

2. Why does tower f. look like a tree?

__________________________________________________________________________ __________________________________________________________________________

3. Explain why a tower with a concrete base is more stable. __________________________________________________________________________ __________________________________________________________________________

4. Which tower do you think looks the most unstable. Explain your answer. __________________________________________________________________________ __________________________________________________________________________

5. Do you think that towers with struts and ties are more stable than those without? Explain your answer. __________________________________________________________________________ __________________________________________________________________________

6. Which of these towers have a: a. High centre of gravity:_____________________________________________

b. Low centre of gravity:______________________________________________

7. What could happen if a tower had the centre of gravity more to one side?

__________________________________________________________________________ __________________________________________________________________________

8. Why do some towers have cables? __________________________________________________________________________ __________________________________________________________________________

Exercise 6: Case study – Advantages and disadvantages of landlines and cell phones. Read the scenario below and answer the questions that follow.

Ben’s parents live on a farm. He goes to boarding school and goes home every weekend. There is no cell phone reception at the farm. Ben needs to phone a friend to find out what homework he has to do for Monday. He has to use the landline but gets frustrated because he cannot hear his friend clearly.

1. Why is it difficult for Ben to hear his friend?

__________________________________________________________________________ __________________________________________________________________________

2. Would Ben experience the same problems with s cell phone if a cell phone tower was to be installed near the farm? Explain your answer. __________________________________________________________________________ __________________________________________________________________________

3. Complete the table below with two examples each for the advantages and disadvantages of using a cell phone and a landline.

Telecommunication device Advantages Disadvantages

Landline 1.

1.

2.

2.

Cell phone 1.

1.

2.

2.

Exercise 7: Examining a cell phone tower. Answer the questions below.

1. List all the features that the cell phone tower has. __________________________________________________________________________ __________________________________________________________________________

2. Think about how the cell phone tower design could be improved and list your ideas. __________________________________________________________________________ __________________________________________________________________________

3. Now write a design brief and specification to make your newly improved design. __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________ __________________________________________________________________________

4. Draw and label a sketch of your newly improved cell phone in the space below:


Term 2 Grade 7: Technology Worksheet Topic: Structures. (Exercises) Question 1 Match the term in Column A with its correct definition in Column B

Column A Column B Answer 1.1 Strut a) To twist or being twisted 1.1

1.2 Tie b) To shape into folds or parallel and alternating ridges and grooves

1.2

1.3 Stability c) A rod or bar forming part of a framework and designed to resist compression

1.3

1.4 Corrugate d) A piece of string, cord, or the like, used for fastening or trying something

1.4

1.5 Torsion e) A state of being stable 1.5

Question 2 Study the illustrations below and then complete the table by identifying whether it is a solid, shell, or frame structure, and whether it is natural or manmade

2.1

Type of Structure: _________________________ Natural or man – made? ____________________________________

2.2

Type of Structure: _________________________ Natural or man – made? _____________________________________

2.3


2.4


2.5


Question 3 Answer the following questions

3.1 Define a structure

_________________________________________________________________________

_________________________________________________________________________ 3.2 Explain how you would strengthen a rectangular frame structure

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

3.3 What two properties of a structure provide good stability?

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

3.4 Sketch a basic frame structure with labels indicating struts and ties

3.5 Which is more stable - a giraffe or a tortoise? Suggest reasons for your answer

_________________________________________________________________________ _________________________________________________________________________

3.6 Explain the difference between push and pull forces

_________________________________________________________________________ _________________________________________________________________________

3.7 Explain using examples, the difference between frame and shell structures.

Frame Structure - ___________________________________________________ __________________________________________________________________ Example: _________________________________________________________ Shell Structure -_ __________________________________________________ _________________________________________________________________

Example: _________________________________________________________

term 2 grade 7: technology worksheet - parkhurst primary

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