Forces & Structures

1. Forces & Structures Grade 7/8 Science Ms. Budzinski

2. Structures • What is a structure? • something that has a definite size and shape, in order to serve a definite purpose or function • to perform its function, every part of the structure must resist forces that could damage its shape or size

3. Classifying Structures • Structures can be natural OR manufactured • Natural: not made by people; occur naturally in the environment • Manufactured: built by people; often modelled after natural structures

4. Types of Structures • Solid Structures • Made of solid pieces of a strong material • Can be formed by piling up or forming similar materials into a particular shape • Natural examples: mountains, coral reefs • Manufactured examples: sand castles, dams, brick walls

5. Types of Structures • Advantages of Solid Structures: • Held in place by their own weight • Losing a small part usually has little (if any) effect on the overall strength of the structure

6. Types of Structures • Frame Structures • Made of a skeleton of strong materials, which is then filled or covered with other materials, supporting the overall structure • Most of the inside part of the structure is empty space • Parts are connected in a set arrangement

7. Types of Structures • Natural examples: human skeleton, spider webs • Manufactured examples: wooden houses, staircases, bicycles • Frame structures are the most common building choice because they are easy to design and materials are inexpensive

8. Types of Structures • Disadvantages of Frame structures: • Weakest points are at joints • Must design braces, anchors and joints so that the structure does not collapse

9. Types of Structures • Shell Structures • keep their shape and support loads, without a frame or solid material inside • use an outer layer of material to provide their strength and rigidity • shape spreads forces throughout the whole structure, so every part of the structure supports only a small part of the load

10. Types of Structures • Natural examples: turtle shell, beaver dams • Manufactured examples: igloos, egg cartons, pop cans • Balloons and parachutes are also shell structures, but they are FLEXIBLE

11. Types of Structures • Advantages of Shell structures: • Completely empty (useful for storage) • Thin outside layer uses less material

12. Types of Structures • Disadvantages of Shell structures: • A tiny weakness or imperfection can cause the whole structure to fail • When the shell is formed from hot or moist materials, uneven cooling can cause some parts to weaken other parts by pushing or pulling on nearby sections • Flat materials are difficult to form into the rounded shell shape

13. Types of Structures • Combination Structures • Football helmets – • Warehouses – • Airplanes –

14. Words to Know The Three different types of structures are… • Frame structure • Shell structure • Solid structure

15. What types of structures are in this room? • In in your table groups, look or walk around the room and try to identify at least 1 of each type of structure. • The more you can find the better. • Fill in the chart on your page as you identify them.

17. Activity • Complete “Structure ID Search” • There are a number of structure pictures placed around the MPR. Your job is to identify each one as one of the following… • Frame • Shell • Solid

18. Force & Center of Gravity • What is force? • The push or pull on an object • What is the “center of gravity?” • The specific point where the mass of the structure is evenly distributed, so that the force of gravity acts evenly on all the pieces • Engineers need to know the center of gravity in order to ensure that their structures are stable

19. Drawing Diagrams of Force • Force is represented by arrows called “vectors” • Longer arrow represents more force • Point indicates the direction of the force • Diagrams do not include all the forces that are acting - usually just show the most important or strong force

21. Activity • Tower Contest! • In groups of 4, build the tallest tower possible with the materials that have been provided.

22. Activity & Exit Slip • Why is it difficult to stand up from a seated position with someone’s hand on your forehead? • You must use the words “balance,”“force” and “center of gravity” to explain your answer

23. Words to Know • Center of gravity • Stability

24. Internal Forces • Compression • The result of forces squeezing together • Ex:

25. Tension • The pulling apart of a structure • Ex:

26. Internal Forces • Shear • Result of forces acting in opposite directions of each other • Ex:

27. Torsion • Twisting force • Ex:

28. Activity • Activity Licorice and Forces

29. External Forces • There are many external forces that can act on an object. • These forces differ depending on the situation or area in which the object is in. • Some common external forces include… • Gravity • Buoyancy • Thrust • Current • Wind

30. What are the external forces acting on the following object?

31. What are the external forces acting on the following object?

32. What are the external forces acting on the following object?

33. Words to Know • Compression • Tension • Shear • Torsion • Internal forces • External forces

34. Assignment • External Forces & Boats • DUE DATE: Thursday, December 17th. • You will be given 10 min to complete this now.

35. Structures & Loads • The effect of forces acting on a structure is called the load • Static • Caused by the force of gravity • Dynamic • Caused by forces other than gravity

36. Effects of Force on Structures • Structural Stress • Occurs when a combination of external and internal forces act on a structure at one time • Structural Fatigue • Occurs when a combination of external and internal forces weaken components of a structure • Structural Failure • Occurs when structure collapses

37. Structural Fatigue on a Bridge in Minnesota • http://www.youtube.com/watch?v=zTz-Pn4xoZg&safe=active

38. The Leaning Tower of Pisa • The Leaning tower of Pisa is located in Italy and it is a major tourist attraction.

40. Assignment • Read “Anti-Gravity in Pisa” • You are going to create a comic strip using the story Leaning tower of Pisa Story. Leaning Tower of Pisa Facts

42. Words to Know • Structural fatigue • Structural failure

43. Application of Force • When force is applied to structures, there are 3 factors that affect the structure 1. Magnitude • measurement of the strength of a force • Shown by length of vector arrow

44. Application of Force 2. Direction • The “push” or “pull” of the force affects what will happen to the structure Example:

45. Application of Force 3. Point of Application • Where the force is applied determines how the structure moves or changes

46. Words to Know • Load • Magnitude • Point of application

47. Activity: Spaghetti Bridge Test • Using the spaghetti given to you, follow the instructions on the activity page and complete the activity. • Make sure to record your data as you go.

48. Strong paper bridge • https://www.youtube.com/watch?v=gtUZcIDrwoo

49. Shapes and Strength • There are many different shapes and they all have their strengths and weaknesses. • Architects need to keep the function of the object in mind when designing it so that they can decide what shapes are needed to be able to function properly.

50. Archs • An arch is a curved structurethat spansa space and may or may not support weight above it. • There are many different types of arches. • After more than 2,000 years of architectural use, the arch continues to feature in many structures. • Its semicircular structure distributes compression through its entire form and diverts weight onto its two abutments, the components of the bridge that directly take on pressure.