# Structures + Forces

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Structures + Forces

1.1.1.1.1. On a tree, the leaves are the live load and the trunk and the branches are the dead load.

1.1.1.1.2. In a car being driven, the humans are the live load and the car is the dead load.

1.1.2.1. Loads that appear unexpectedly and can change over time.

1.1.2.1.1. When a car is driving on a bridge and the car is the dynamic load on the bridge which is the structure. The car isn't always there and is always on the move. That is why it is a dynamic load instead of a live load.

1.1.2.1.2. A Helicopter on a building(taking off), the helicopter is a dynamic load, and the building is the structure/dead load,

1.2.1.1. The structure itself without any live load or changes.

1.2.1.1.1. If a person is lifting weights, the weights are the live load and the person is the dead load.

1.2.1.1.2. If a crane is lifting materials, the crane is the dead load and has to support it's own weight and the materials it is carrying are the live load.

## 2. Types Of Forces

### 2.1. Internal Forces

2.1.1. Shear

2.1.1.1. When the structure is being pushed in opposite directions.

2.1.1.1.1. Tectonic plates moving in opposite directions causes an earthquake which has shear force activating on it.

2.1.1.1.2. Ripping paper causes there to be shear force, as one hand is pushing it down in one direction, and the other is pulling it way.

2.1.2. Tension

2.1.2.1. When the structure expands by being pulled making it longer/taller.

2.1.2.1.1. When you play a game of tug-of-war, the rope experiences tension because it is being pulled in opposite directions, making it stretch.

2.1.2.1.2. When you pull a rubber band, the band experiences tension because you are pulling it apart

2.1.3. Torsion

2.1.3.1. When the structure is being twisted, by twisting it in opposite directions.

2.1.3.1.1. When you twist a towel, there is Torsion being impacted on the middle of the towel when it is twisted both ways.

2.1.3.1.2. When you are twisting a rubiks cube, it experiences torsion, because both sides of the cube are twisted both ways, affecting the middle.

2.1.4. Compression

2.1.4.1. When the Structure has a force pushing down on it making it smaller.

2.1.4.1.1. When you push down on a cake with your foot, it gets flattened, and compression takes place because you are squishing it

2.1.4.1.2. When you push down on a car with a car crusher, it creates compression because the force of the crusher is on the car flattening it.

### 2.2. External

2.2.1. Gravity

2.2.1.1. A massive force for the Earth that pulls everything towards the middle of the planet.

2.2.1.1.1. When you drop a ball from a building, gravity impacts it because the ball will not float in mid air, because gravity is impacting it and so it will fall down.

2.2.1.1.2. When you drop a microphone off a stage, it will fall since gravity is impacting it and it will hit the ground, it does not stay afloat since Earth has gravity.

2.2.2. Friction

2.2.2.1. When the surface of two objects meet each other while moving.

2.2.2.1.1. When you rub a chalk eraser on a chalk board, it creates friction, because you rub two objects together creating the force which is known as, friction.

2.2.2.1.2. When you rub soap against the wall to get rid of a certain stain on the wall, that is also friction, since you are rubbing an object against another object.

2.2.3. Dynamic

2.2.3.1. Forces that come and go and wouldn't expect to always be there.

2.2.3.1.1. Wind is a dynamic force because it can be there sometimes but not all the time, as it will go away with time.

2.2.3.1.2. Let's say that a student is carrying a bunch of textbooks. The student would be the dead load and the books would be the live load. But if the student were to start walking, that force of him/her moving would be the dynamic force.

## 3. Reasons for Structures

### 3.1. Form

3.1.1. The overall shape and outline of how the structure is designed. (made for the looks)

3.1.1.1. The Bank of America Tower, located in New York, is a pretty outstanding skyscraper in that city. In contrast, a building needing that many materials and time to build is just not worth it for a banking office.

3.1.1.2. The Portland Building is a municipal office work place that has all the things needed to make the office run smoothly. Although it is not the most beautiful structure, it is able to sustain a proper work place.

### 3.2. Function

3.2.1. The purpose the structure serves and the reason for why it was built.

3.2.1.1. The Great Wall of China was first built to keep invaders out. It is made out of soil, dirt, mud, and mainly stone. It is a very strong and stable structure and is currently now one of the best "Wonders of the World" Unfortunately, it can't compare its looks with modern skyscrapers today.

3.2.1.2. On the other hand, the tallest building in the world, Burj Khalifa, is quite underestimated on its uses compared to its looks. Despite that it's an extraordinary building, it is mainly not inhabited and is basically useless to the people around except for tourism.

## 4. Types Of Structures

### 4.1. Shell Structure

4.1.1. A hollow structure, with space inside that is usually light

4.1.1.1. An egg is an example of a shell structure, because it is hollow on the inside, but it can hold stuff.

4.1.1.2. An igloo is also an example of a shell structure as it is hollow on the inside and it can hold lots of objects as people live in it

### 4.2. Frame Structure

4.2.1. A structure that is made from parts joined together

4.2.1.1. The frame of a car is a frame structure, because all you can see is the frame of it, and not an actual car with the outside of it.

4.2.1.2. A bike is an example of a frame structure, as it has only a frame for the structure and there isn't much more to the average bike.

### 4.3. Solid Structure

4.3.1. A structure that has no space inside, and its strong

4.3.1.1. A mountain can be an example of a solid structure, as it is solid all the way through (most of the time since some mountains have holes.)

4.3.1.2. The Statue of Liberty is a completely solid structure because it is very heavy and have no space between or inside it.

### 4.4. Combination Structure

4.4.1. A very strong structure that uses all the structures combined

4.4.1.1. A house is a combination structure because it is made up of shell, frame, and solid structures. The walls and ceiling of the house and the hallow inside makes it a shell structure. The wooden beams and supports act as a frame structure, and the thick walls and floor are solid structures

4.4.1.2. A human is actually a combination structure. Your skeleton are the frame structure, your lungs are a shell structure, and your organs and brain are solid structures.

## 5. Parts of a Structure

### 5.1. Centre Of Gravity

5.1.1. The point of a structure where the entire weight is considered as concentrated and stable

5.1.1.1. Think of a pyramid in Egypt. The top is very small and light, but the bottom is heavier and wider than the rest of the structure. This part is called the base, and since most of the structure's weight is there, it is the center of gravity.

5.1.1.2. In a person, the center of gravity is near the stomach, since most of the weight of the person is concentrated there.

### 5.2. Materials

5.2.1. Matter and substances that make up the structure. Some materials are stronger and can withstand forces better than others.

5.2.1.1. Building a castle out of stone is better than wood because it is more stable, balanced, and can't be lit on fire. People realized that building their castles using stronger materials are very useful against enemy invasions.

5.2.1.2. Imagine that you are building a boat, you will need very strong materials enough to withstand the weight of the person riding it and the current of water it is flowing through. Using wood or reeds would not be the best choice because it is not strong to hold together. Steel or fiberglass would be a better choice.

### 5.3. Structural Shapes

5.3.1. Parts of the structure's frame that vary in shape and size.

5.3.1.1. When building a house, a construction will have very different parts of materials to work with. Have you wondered why roof-tops are made slanted? It's because the slopes on either side lets rain-water and snow slide down so that it wouldn't pile up and break the ceiling.

5.3.1.2. When people build complex bridges, did you ever realize that the steel frames are usually "X"s or triangles. This is because the sides of a triangle are harder to be compressed and bent, also the "X"s provide extra support with the steel rods crossing. These shapes are way more stable that rectangles or squares.

### 5.4. Stability

5.4.1. A state when the whole structure is well balanced or when it is very fixed and firm.

5.4.1.1. A see-saw is stable when the weights on both sides are equal. This is so that it doesn't tip over when one side weights more that the other.

5.4.1.2. When grocery store employees arrange their products on top of each other, they need to think of the stability. If it is not stable, then the whole thing will come cashing down.

## 6. Describing forces

### 6.1. Plane & Point of Application

6.1.1. Where the force hits the structure. (top, bottom, side, ect.)

6.1.1.1. If you want to destroy your friend's Lego tower, you will most likely be aiming at the bottom. Most of the tower's weight is there and it's the bottom do all of the blocks on top will fall easily. Whereas if you hit the top, only that part of the tower will fall.

6.1.1.2. If you want to take out a stack of textbooks out of your locker, you will most likely hold onto the bottom book. This is because that is where most of the weight is so that the rest don't fall out of your hands

### 6.2. Direction

6.2.1. Which direction the force is coming from. (90*, 180*, 45*)-(in front, side, diagonally)

6.2.1.1. When you use a crane to destroy a wall, it will most likely to be hit at a 90* angle (in-front.) This is because the wall is thicker if you smash it on the side and the diagonal angle.

6.2.1.2. When you get into a car crash, if you smash your car head-on, then there will be more damage because the engine is there and it will most likely compress with the object hit. If you get hit on the side, then it is often less severe because it will only damage the doors.

### 6.3. Magnitude

6.3.1. How big/ fast the force is when it hits the object

6.3.1.1. When you kick into a punching bag, the more power you use, the stronger the force, and the bag is going to move more. But is you use less power, there will be less force and the bag might not even move.

6.3.1.2. When you throw a ball, if you throw it hard, then it will travel faster through the air and when it hits the object. But is you just toss it, there won't be as much speed as when you whip it.