SCIENCE in Action7

Unit D:

Name: Miss Cardamone

Class Pattern: 7H

Structures and Forces

1.0 – Structures are found in natural and human-made environments.Every object that provides support to something is a

structure. A structure may be made up of one or more parts, and it can be large or small. Structures can be found in the natural environment or some are built by people.

Structural strength refers to a structure’s capacity to hold itself up, along with any

added weight. Structural stability is a structures ability to maintain its position even when it is being acted on by a force.

1.1 Classifying Structural Forms - There are three basic structural forms. Complete the following three charts, provide a picture for each type of structure a description and pictures of man-made and natural examples (you can find photos in a magazine or on the internet.)

Solid Structures:

DescriptionMan-Made Example

Natural Example

- A solid structure is formed from a solid piece (or a solid combination of pieces) of some strong material. - Solid structures are usually stronger than either frame or

- Brick Wall- Hockey puck

- Apples - Trees

shell structures.

These structures are not always completely solid. Inside structures like dams, there can be large rooms that hold the turbines and generators. This means that these structures have to be very carefully designed to suit their purpose.

Frame Structures:

DescriptionMan-Made Example

Natural Example

- A frame structure is made up of a rigid arrangement of parts or structural components, fastened together. - Compared to solid structures, frame structures are lighter because they use less material.

- Towers (signal)

- Wheel Chair

- Skeleton (made up of

bones, ligaments and

joints)

Certain kinds of this structure present special design challenges. Tents and other lightweight structures need some type of anchor to hold them

down. Very tall frame structures, like a signal tower, can be very unstable if they are not braced properly.

Shell Structures:

DescriptionMan-Made Example

Natural Example

- A shell structure has a solid outer surface, which may be rounded or flat in shape, and a hollow inner area. - Shell structures with a rounded outer surface are usually stronger than those with a flat outer surface, because the curved areas distribute the load around the whole surface.

- Flower pot- CD case

- Tennis ball- Bean pod

Constructing strong versions of this type of structure can be very tricky.

1.2 – The Function of Structures Multiple Functions – Many structures are designed to serve more than one function. Function and Effective Design – Technological problems can often be solved in a variety of ways, using many different structural designs, materials and processes. All successful solutions pay close attention to function. To get ideas for structures that will meet particular functions, designers, architects and inventors look at the natural world for ideas. Common Function, Different Design – Structures may look different from one another in design but their function is often very similar. All roof designs are effective in their own way if the suit the local climatic conditions and meet the needs of the people who use them. Other Characteristics of Structures – In addition to form and function, structures can be classified according to the materials and components they are made out of. Designers plan their structures to withstand the different conditions they might encounter.Aesthetics – The term Aesthetics refers to the pleasing appearance or effect than an object has because of its design.

People around the world have traditionally decorated their houses on both the outside and inside. Today, people continue to design and embellish their dwellings and other buildings so that they look attractive.

2.0 – External and internal forces act on structures.2.1 – Measuring Forces

A force is: a push or pull that tends to cause an object to change its movement or shape.

Magnitude, Direction, and Location – The effect of a force on a structure depends on three things, what are they?

1. The magnitude, or size, of the force. 2. The direction of the force. 3. The location where the force is applied.

The bigger a force’s magnitude , the stronger it is and the more effect it will have on a structure.

The direction in which a force acts on a structure also determines what effect it will have.

The location of where a force is applied on a structure affects the outcome.

The Newton – What is a Newton (N) ? One Newton is the amount of force needed to hold up a mass of 100g.

If one newton is the amount of force that is needed in order to hold up a mass of 100 g holding up a 1 kg book would therefore require how many newton’s of force? 10 N.

2.2 External Forces Acting on Structures – An external force is a force that is applied on a structure by something else. For example when walking into a wind or standing in waves, the force you feel acting on your body is an external force. Mass is the amount of matter in an object. The more mass an object has, the greater the gravitational force on it.Centre of Gravity – Gravity acts on all parts of a structure and there is a point at the centre of a structure that if it is supported it will stay balanced and this point determines the structure’s stability .

Symmetry is: a balanced arrangement of mass on opposite sides of a line or plane , or around a centre or axis. For a symmetrical structure to be stable, its mass must be distributed equally around the centre of the structure’s base. This also means that the force of gravity around the centre is also equal.

Load is: an external force on a structure. The weight of the structure and the non-moving load it supports is called the static load. These are forces that stay the same for a long period of time. (Static means not moving or changing.) Another term for static load is a dead load.A dynamic load is an external force that moves or changes with time. These loads can change very quickly as occurs with a gust of w ind or an earthquake. Another term for a dynamic load is a live load .Designers must plan structures to be capable of resisting both dynamic and static loads. What two things must engineers consider when they decide the type of bridge to build?

1. What the bridge is crossing (e.g., water or land) 2. What kinds of loads the bridge will be supporting.

Bridges - There are several different types of

bridges – in the next section you will explore them and discover what makes each design unique to the other.The beam bridge is flat and is supported at its two ends . A longer beam bridge may be supported by additional piers or vertical supports .Draw an example of this type of bridge in the space below.

A truss bridge is a lightweight but strong bridge made of trusses or triangle shaped frames along its sides.

Draw an example of this type of bridge in the space below.

A suspension bridge hangs between two ends that hold it up. It will have tall towers at each end that support the main cables holding up the bridge. Smaller cables which support the roadway, are suspended from the main cables.Draw an example of this type of bridge in the space below.

An arch bridge is designed to carry heavy loads.Draw an example this type of bridge in the space below.

Measuring a Structure’s Load Performance – Engineers set conditions that a structure must meet after it is built to show it is performing to certain standards. These standards are called the performance requirements. These include the maximum weight , the safety of the structure and the effectiveness in meeting the purpose for which it was designed.

2.3 Internal Forces within Structures – What is an internal force?A force that one part of a structure exerts on other parts of the same structure or simply put they are forces that act within a structure.

Compression, Tension and Shear – Internal forces can be classified by the direction in which they act within an object. There are three internal forces what are they and how do they work?

Compression- a force that acts to squeeze an object or push parts within an object together

Tension- a force that acts to stretch and pull apart something.

Shear- a force that acts to push parts that are in contact with each other in opposite directions.

Complementary Forces – When different kinds of internal forces act on a structure at the same time, they are called complementary forces.

2.4 Designing Structures to Resist Forces and Maintain StabilityStrong Structural Shapes – Of a square, rectangle or triangle, which is the strongest three dimensional shape? Triangle Structural Components – The textbook discusses three types of structural components, what are they and explain what makes them important components in any structure.1. Arch- can support a large load because the force of

the load is carried down through the arch to the foundation.

2. Beam- flat structure that’s supported at each end3. Column- solid structure that can stand by itself.

Columns can be used to support beams.

3.0 – Structural strength and stability depend on the properties of different materials & how they are joined together.3.1 – Materials and Their PropertiesClassifying Material Properties – Materials that are used in structures are classified or evaluated according to their .Copy the chart on the bottom of page 309 in your text in the space below:

Some Properties of Materials

Other Considerations

Testing Deformation and Flexibility of Materials in Structures – Any time you design and a structure, you will use materials that have enough strength to the forces on the structure.

What does the term Deformation mean? Flexibility is:

3.2 – Joining Structural Components – The place were structural parts are joined is called the . At times this place must be , or fixed, in order for the structure to work properly. At other times this point needs to be flexible, or .Joints That Rely on Friction – Friction is:

The strength of friction also depends on the or smoothness of the two in contact with each other. To create strong joints between parts of a structure the of friction can be used to prevent the individual components from apart.

Nails, Screws, Rivets, Tacks Staples - When a nail, screw, rivet, tack, or staple is used to hold components

together it is the between the metal and the material it that does the job.

Interlocking Pieces - You can increase the amount of friction by the area that comes into contact. Interlocking pieces do not need or to join things together.Mass - The friction between two of something that is very heavy or has Mass can be joined together only by the of friction. Joints That Rely on Bonding – Two surfaces can be joined so that they are connected by a common material. Adhesive glue and , cement and welds act to the surfaces of materials. Fixed or Movable? Which Joint for Which Structure?

Fixed Joints are to prevent any . Movable joints are or mobile so that parts of the structure are still able to if required.Designing Joints to Last – For some structures the main forces acting on them are conditions (heat and cold, rain, and snow). Structures with moving parts must be able to survive the force of movement or the structure will cause it to fail.

3.3 – Properties of Materials in Plant and Animal Structures

Materials in the Human Structure – Each of the components in the human body is a unique with special properties suited to the of that part. Bones are hard and and form the frame that is strong enough to and protect the parts of the body. Bones are connected together by . Cartilage at the end of

some bones reduces and helps to protect the of your bones when they into each other.Muscles of which there are , allow you skeletal structure to .Joints are specialized for various . Ball-and- , and gliding are examples of various types of joints.Skin is a tough, material that provides structural and regulates the of the body.Materials in a Tree’s Structure – A tree trunk is a structure made up of several different of different material. Draw & label the different layers of material in a tree branch in the space below.

4.0 – Structures are designed, evaluated, and improved in order to meet human needs.

4.1 – Building Safe Structures in All EnvironmentsMargin of Safety – Safety is important to all designers they work with a margin of safety what does this term mean? Testing occurs at stages of a product’s development, from choosing and testing its , to testing the and then the final product before it is given approval for the consumer to . By monitoring how a structure performs, information can be gathered to decide how a structure can be.Accounting for Environmental FactorsClimate Conditions must always be when designing a structure. Buildings, , vehicles, and other outdoor structures must withstand the forces of , rain, and as well as heat, cold, and dryness.Terrain Conditions - Unstable & terrain can make building a structure .Earthquake Risk – In areas where are a risk, the structures must be designed and to resist the external and internal acting on them.

4.2 – Strengthening Materials to Improve Function and SafetyAltering Materials for Strength – Combining materials and into new can solve structural problems. This takes advantage of the best of each material. In the space provided give an explanation for each term.

Corrugation: Lamination: Strengthening Component Arrangements: Changing Methods of Fastening: New Materials – New materials are being all of the time, many provide solutions to the challenges of building , lighter, and more structures.4.3 – Evaluating Designs from an Overall Perspective

A Case Study in Improving Designs

Read page 335 in the textbook about Rocky Mountain Bicycles and then answer the following questions.

1.Give an example of a design change that the company makes to its bikes, and on what customers liked. How did the company get this information?( 3 Points)

2.Why are triangles used in the frame of the bicycle?(1 Point)

3.What efforts does the company make to help create a sustainable environment? Why is this important?(2 Points)

4.A designer might have to choose between the material with the best properties and a more economical material. Why? Give an example of how Rocky Mountain Bicycles does this. What would you predict might happen if a new, recycled plastic material that was light but strong as steel were developed? (3 Points)

5.Why does this company invite trade magazines to test and evaluate its bicycles?