U NIT 4 Structures & Forces

U NIT 4 Topic 1 Types of Structures

W HAT IS A STRUCTURE ? Structure Something with a definite shape and size which serves a definite function or purpose

W HAT IS A NATURAL STRUCTURE ? Natural Structure Something that is not man made Follows the same definition of a structure

W HAT IS A MANUFACTURED S TRUCTURE ? Manufactured Structure Something that is created by man Follows the same definition of a structure

W HAT IS A M ASS S TRUCTURE A structure made by piling up, or forming, similar materials into a particular shape or design – can be natural Follows the same definition of a structure

H OW CAN A MASS STRUCTURE FAIL ? There are 4 ways a mass structure can fail … Let’s use a sandbag wall for example! 1) The wall is not heavy enough and forces on it push it over 2) The wall could be too heavy, move the earth underneath it, it becomes uneven and topples 3) The wall could be put together poorly resulting in weak links. Certain pieces fall out and wall falls 4) Not anchored to the ground and the external forces will knock it over

W HAT WOULD A LOAD BE ? Load Weight carried or supported by the structure

F RAME S TRUCTURES What is it? A structure with a skeleton like frame Always made of strong materials Can support huge amounts of weight … if built properly of course!

F RAME S TRUCTURES

F RAME S TRUCTURES C ONT … All frame structures are not the same Objects such as ladders, snowshoes and spider webs are only frames That is to say are full of important pieces More complex objects often attach things to the frame Think a bike … frame is what you sit on and it supports you but we add… Braking system Steering system Suspension systems Pedals

F RAME S TRUCTURES C ONT … Frames can also be hidden … Like in an umbrella or a car Or exposed (out in the open) Like a drilling rig or bridge

S HELL S TRUCTURES Strong and hollow Keep their shape Support loads even without a frame or solid mass of material inside

S HELL S TRUCTURES C ONT … 2 Major Benefits of this structure 1) They are completely empty which makes them great containers 2) They are made up a thin layer they use very little building materials But how does it work?

S HELL S TRUCTURES C ONT …

So if they are cheaper and very strong – why don’t we build everything into a dome shape?! As strong as they are they face many different challenges to be constructed perfectly! 1) Tiny weaknesses cause the whole structure to fail!

S HELL S TRUCTURES C ONT … 2) If it is formed and constructed out of hot or moist materials (think clay for example) and dries or cools unevenly you can push or pull in neighboring sections This causes structural weak points and out of no where it could break!

S HELL S TRUCTURES C ONT … 3) Think of trying to build a plywood igloo! Many of our construction materials are not designed for this type of construction Each piece would need to be shaped individually Crazy expensive!

S HELL S TRUCTURES C ONT … 4) Assembling the finishing materials into a shell is also very tricky It needs to be pinned and held in place in a specific way Then all the edges need special finishing Crazy expensive again!

M IX & M ATCH To make the best of both worlds many structures in the world mix and match the principles of both designs together Part Frame Structure Part Shell Structure How does this work?

U NIT 4 Topic 2 Describing Structures

F UNCTIONS Structures perform a variety of different jobs … here is a list of the most common. Can you think of a real world example of each? Containing Transporting Sheltering Lifting Fastening Separating Communicating Breaking Holding

F UNCTIONS The first thing all designers/builders think is … “What is this thing supposed to do” However is it that simple? No way! Structures often have many different functions What are the functions of a house? What are the functions of a bridge?

F UNCTIONS C ONT … Often, as much as we want the designs to be perfect, when we add multiple functions they are not perfect Think of a shoe (see pg: 283) What are the functions of a shoe? What happens if we try to water proof a shoe?

A ESTHETICS What are aesthetics? How good it/they look of course! Aesthetics is actually the study of beauty in art and in nature Building materials are key in this? Concrete vs. Marble? Also, remember the KISS principle Keep It Simple Stupid!

S AFETY Picture an elevator … or look at this! What is the key thing on this panel? All structures are designed with safety in mind! Elevators are designed to hold more than it could fit for safety

S AFETY Elevators have extra strength that allows it to withstand much larger loads than it would normally need to carry Large safety margin! Safe for riders in almost all situations

B ALANCE Making things safer typically means more expensive Sometimes … builders / designers try to take the easy way out and cheap out – no good! Also, designs typically take into account events they assume will occur (flood, wind, etc …) Rare and unexpected events are tough to plan for because there are so many things that could happen! OopsOops!

M ATERIALS So … as you have seen there is a lot of thought that goes into designing something. Once you have a design it is time to determine what type of materials you will use to construct it Let’s explore the most common categories …

C OMPOSITE M ATERIALS There are different kinds of strength… Tension (pulling)  Steel rods Compression (pushing)  Concrete To enable the structure to withstand both types of forces acting on it, a composite material is used Composite is essentially a combination of materials R einforced concrete Concrete poured over steel rebar (rods).

L AYERED M ATERIALS Pressed and glued together Combining the properties of the different materials. The layers are often called laminations. Did you know this about pop cans and canned foods?

W OVEN / K NITTED M ATERIAL Spinning or twisting, looping or knotting fibers together gives material added strength A loom is used to weave two or more pieces of yarn together in a criss-cross pattern to make cloth Pressing, gluing, melting and dissolving are also ways to combine materials to gain strength.

C HOOSING M ATERIALS When choosing materials it is about … Weighing advantages vs. Disadvantages For example… Higher quality & stronger materials are usually more expensive So here are the most common factors to consider!

F ACTORS TO C ONSIDER Cost Will inexpensive materials allow the structure to perform its function over a reasonable time? Appearance Is the appeal of the structure ‘pleasing' over time? Environmental Impact Does the structure harm the environment Energy Efficiency Does the structure conserve energy?

J OINTS How would you define “Joint” How do you fasten the structure together? Are there different kinds of joints? All this and more on today’s lesson … JOINTS

T YPES OF J OINTS Mobile Joints Joints that allow movement Rigid Joints Joints that do not allow movement

F ASTENING Fasteners Devices that hold two, or more, things together Ex: nails, staples, bolts, screws, rivets and dowels Unfortunately, the holes made in the structure, by the fastener, actually weaken the structure One fastener allows movement when the parts are pushed or pulled More than one will make a more rigid joint - but, will also weaken it more.

I NTERLOCKING Interlocking shapes Fit together because of their shape Examples Dovetail joints in drawers, dental fillings, Lego

T IES Ties Essentially a form of fastening Examples Thread, string and rope

A DHESIVES Adhesives Sticky substances can also hold things together. Thermosetting glues  hot glue Solvent-based glues  drying glue Strengthen the joint because of the bonds between the particles Even the strongest adhesives can fail under extreme conditions … if the joint is stronger than the material it is joining, the material next to the joint can fail. Adhesives can also be a health hazard

M ELTING Melting Pieces of metal or plastic can be melted together Examples Welding, soldering - brazing or using chemicals

U NIT 4 Topic 3 Mass & Force

M ASS VS. W EIGHT So this is the time we learn something very important … mass … that is what is mass ? weight … that is what is weight ? Let’s go!

M ASS Think back to the particle theory! All things are made up of particles right? Can you guess where I am going with this…? The mass of an object is the measure of the amount of matter in it The mass is the number of particles the substance has

M ASS – U NITS OF MEASURE ? To set the standard … A small cylinder of metal was used by which, to compare different substances. This standard (in the metric system) is called the primary standard of mass, and the amount of material in it is called one kilogram (kg). Smaller masses are measured in grams (g). 'Kilo' means one thousand (1000) and is equal to 1000 grams. Very small masses are measured in milligrams (mg) mg. equal 1 g.

M ASS – T HE S TANDARD TO M EASURE A balance is used to measure the amount of mass in a particular substance Standard scientific balances include the triple beam balance and the equal arm balance.

M ASS – I N SUMMATION How much would your mass be on Earth compared to the moon? Trick question it stays the same … the big idea is… No matter where you are in the universe your mass stays the same!

F ORCES & W EIGHT Force is a push or pull on an object The standard unit of force is called a Newton (N) (1 newton of force will stretch a thin rubber band, or will be what it takes to lift up a D-cell battery) A force meter ( spring scale ) is used to measure the amount of force - the pull of gravity - on a mass. To describe a force accurately, you need to determine its direction and size.

W EIGHT & G RAVITY Time to play with spring scales!

W EIGHT Weight is a force and should properly be measured in newtons Sir Isaac Newton described the force that pulls objects together as the force of gravity The gravitational forces between two objects depends on the masses of the objects and the distance between them This gravitational force is called weight Because gravitational force depends on the distance between two objects, an object's weight changes depending on where it is. (the farther away from the earth, the less the weight.

R EMEMBER !! Mass is the amount of matter an object is made of Weight is the force with which gravity pulls on an object.