Science Unit 2 (By moi!!)
Understanding Structures and Mechanisms: Form and Function Unit 2
Overview of the Unit
Focus Questions:
What are the best materials to use for building the best structures?
How does the structure of an object dictate its function?
Key Considerations in Design:
Structures must work effectively and be strong and durable.
Environmental considerations, while important, are secondary to functionality and strength.
2.1 Defining Structures
(Refer to Chapter 4.1 for today's lesson)
Definitions
Structures: Objects made up of parts arranged in a specific way for particular purposes.
Can be natural (e.g., trees) or man-made (e.g., buildings, bridges).
Form: The basic shape of a structure.
Example characteristics: four legs, slanted roof, flat roadway.
Function: The intended job of the structure.
Examples of functions: support weight, block wind, connect land.
Classifying Structures
Structures can be classified based on:
Function: What it does.
Construction Type: How it’s made.
Characteristics: Its unique features.
Types of Structures
1. Solid Structures
Description:
Solid all the way through with little to no space inside.
Generally the strongest type of structure.
Examples:
Bricks, wood, apples.
2. Frame Structures
Description:
Composed of parts fastened together with strength derived from the arrangement of these parts.
Components:
Parts referred to as structural components.
Examples:
Framing of a house, scaffolding, greenhouses.
3. Shell Structures
Description:
Strong, hollow, and lightweight with space inside, making them effective containers.
Rounded outer areas enhance strength.
Examples:
Eggshells, igloos, boxes.
Combining Structures
Structures often comprise a combination of solid, frame, and shell types.
Purpose:
To enhance the overall strength of the structure.
Examples:
Play structures, houses, skates.
Your Turn
Activity:
Classify given structures as solid, frame, or shell.
Identify combinations of structures used in the examples provided.
Unit 2.2: Focus on Forces
Types of Structures
Identification: Each type of structure can be categorized as:
Shell Structure: Hollow structures that can withstand loads and maintain shape.
Solid Structure: Made entirely of solid material, with no hollow spaces.
Frame Structure: Composed of interconnected components that provide support.
Forces
Definition: A force is defined as a push or pull that can change the shape, speed, or direction of an object.
Measurement Unit: Forces are measured using the unit Newtons (N).
Structural Design: Structures must be designed to withstand various forces to ensure stability and safety.
Characteristics of Forces
Magnitude: Refers to the size or strength of the force.
Direction: Indicates the origin or path of the force's influence.
Point of Application: The exact location on the structure where the force acts.
Plane of Application: The face or side of the structure that is affected by the force.
Labeling Forces in Diagrams
Instructions for Diagrams:
Direction of the Force: Label with a blue arrow.
Point of Application: Mark with a green dot.
Plane of Application: Indicate with a yellow line.
Force Diagrams
Definition: Diagrams that illustrate the forces acting on an object.
Components of Force Diagrams:
Arrows represent the magnitude and direction of forces.
Arrows are drawn from the center of the object outward.
The length of the arrow corresponds to the force's magnitude.
All forces must be labeled, such as:
gravity (force due to gravity)
Fair resistance (air resistance)
Example Situations:
a) A rock falling from a cliff.
b) Pushing a box to the right.
c) A car stopped on a bridge.
Understanding Structures and Mechanisms
Form and Function Unit 2.3
Internal and External Forces
Page 1
Overview of internal and external forces affecting structures.
Page 2
Review activity: Draw the forces acting in various situations to understand their implications.
Page 3: External Forces
Definition: External forces act on an object from outside.
Gravity: Natural force of attraction between two objects; it is classified as an external force.
Examples of External Forces:
Wind: Blowing leaves.
Push: Pushing a box.
Impact: Hitting a ball.
Page 4: Loads
Definition: All structures need to support a load, which consists of forces acting on them.
Types of Loads:
Static Load: Effect of gravity on a structure (e.g., weight of the structure itself).
Dynamic Load: Forces that move or change while acting on the structure (e.g., vehicles driving over a bridge).
Design Consideration: Structures must support both static and dynamic loads for stability and safety.
Page 5: Practice on Loads
Dynamic and Static Loads Examples:
Dynamic Load: Force of wind, weight of a car.
Static Load: Weight of the bridge (gravity).
Dynamic Load: Weight of books on a shelf.
Static Load: Weight of bookcase (gravity).
Dynamic Load: Weight of a person sitting.
Static Load: Weight of chair (gravity).
Page 6: Internal Forces
Definition: Forces caused by parts of a structure acting on one another.
Determining Factors: Influenced by how a structure is used or constructed.
Examples:
Roof compressing the walls.
Torsion forces inside a structure (e.g., in a skater).
Compression forces on shelves.
Page 7: Types of Forces
Compression: Squeezes or presses something together.
Tension: Stretches apart to expand or lengthen.
Torsion: Twists the material.
Shear: Pushes materials in opposite directions.
These forces can be either internal or external depending on the point of application.
Page 8: Practice on Forces
Forces Identification:
Shearing: External force (hands).
Torsion: Internal force.
Compression: External force (person).
Tension: External force (hands).
Focus on Form and Function in Unit 2.4 Stability
Stabilizing Structures
Stability:
The ability of a structure to maintain or resume its position when an external force is applied.
Factors Affecting Stability
Stability depends on three key factors:
Materials Used:
Comparison of materials such as cardboard vs. wood.
Construction Techniques:
Hand saw versus electric saw impacts effectiveness.
Shapes Used in Design:
Different shapes like triangles and squares influence strength.
Implication: Most stable structures last long due to strong materials, good construction techniques, and robust shapes.
Practice on Structure Strength
Analyzing which structure is stronger and identifying the stability factor that contributes to its strength.
Shape Investigation
Activity:
Build structures out of straw, supporting one side with a finger.
Use another finger to push one side to test stability.
Goal: Determine which shape exhibits the most stability.
Strong Shapes
Examples of Strong Shapes:
Triangles, arches, cylinders, and domes (egg-shaped) are among the strongest shapes.
Strength Analysis:
These shapes withstand forces better than squares and are more effective in three-dimensional forms than two-dimensional forms.
Surface Area: A larger surface area allows force distribution, enhancing stability.
Improving Structural Strength
Assessing structures:
a) Square
b) Roof of a house
c) Ceiling of a large room
d) A sagging bridge
Structural Components
Adding Components for Strength:
Structural components can either work together or individually to enhance a structure’s strength.
Key Structural Components
Beam:
Flat structure supported at either end; prone to bending or breakage under excessive load.
I-Beam:
Its shape offers strength while using less material, making it lighter.
Less inherent weight allows support of larger loads.
Girder or Box Beam:
Long beams shaped as hollow rectangular prisms.
Provide some strength but less than solid beams.
Column:
A solid structure that can self-support.
Used to support beams, and works effectively when combined with beams.
Cantilever:
A flat structure supported at only one end.
Often used to support shelves or structures extending beyond their support.
Truss:
A rigid framework of beams usually in interconnected triangles.
Arch:
Curved structure that directs force along its sides to supports or abutments.
Abutments: Support the arch on one side.
Corrugated Materials:
Made from pleats or triangles, stronger than flat sheets.
Centre of Gravity
Definition:
The point at which a body’s mass is concentrated.
A body is balanced in all directions at the center of gravity.
Bridge 1: Beam Bridge
Less than 80m
Pros:
Inexpensive
Easy to build
Can be built using a lot of different types of materials
Requires the least amount of material to build
Cons:
Weakest bridge
Shortest span
Ships cannot pass under
Not considered to be aesthetically pleasing.
Bridge 2: Truss
50-100 m long
Pros:
Very strong
Often used as a lift bridge
Truss can be built a variety of ways
Cons:
Difficult to build
Difficult to widen
Not considered to be asthetically pleasing
Expensive to maintain
Bridge 3: Arch
Less than 300m
Pros:
No piers can be in the water
Can be built high to allow for easy ship traffic
Can be built using a lot of diffrent types of materials
Very strong and stable
Cons:
Abutments must be placed on solid land to prevent the bridge form flattning
Somehwat expensive to build
Can be time consuming to build
Bridge 4: Suspensions
Greater than 2400m
Pros:
Can span long distances
Can be built high to allow boats to travel under
Considered asthetically pleasing
Very Strong
Cons:
Boats need to avoid the piers (Underwater columns) placed in the water
Most expensive bridge to build
Requires a lot of materials to build
Takes a long time to build
Bridge 5: Cable Steyed
Pros:
Very strong
Modern looking and considered asthetically pleasing
Can span longer ranges than arch and beam bridges
Can be built high to allow for ship traffic
Can be built with less material, faster, and less expensive than a suspension bridge
Cons:
Boats need to avoid the piers (Underwater columns) placed in the water
More expensive than a beam, arch, and truss bridge
Takes longer to build than arch or beam bridge
Hookes Law (Unit 6??)
Elasticy and Elasticity limit (How long it can stretch). Before it becomes deformed