# Structures and Forces

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Structures and Forces

## 1. Types of Structures

### 1.1. Solid structures are structures that use solid construction to support loads, and usually have a large mass.

1.1.1. The Great Wall of China is built with many strong bricks to protect from invaders, so it is a solid structure.

1.1.2. Hoover Dam is very strong and solid to keep water from one side of the dam from flowing to the other side.

### 1.2. Frame structures are composed of a network of materials that support each other and spread the load.

1.2.1. A camping tent is made up of many rods, which act together to split up the load. The membrane, or the tent material, does not help support the weight.

1.2.2. The crane in the image above uses a network of metal rods to support the weight of the crane and the live load is needs to carry.

### 1.3. Shell structures use a curved surface, which spreads the load equally and in return provides high strength and flexibility.

1.3.1. Helmets are shell structures, so when an external force is applied to the helmet, the load is distributed equally throughout; no one part is particularly damaged.

1.3.2. An igloo is a domed shape, so like a helmet, spreads the load. The weight from the top travels down to the ground.

### 1.4. Combination structures are a combination of 2 or more types of structures, and usually benefit from the strengths of the different types of structures.

1.4.1. The Sydney Opera House is solid brick at the bottom; but the arches on the top are examples of a frame structure, since they are working together to support the load.

1.4.2. The Human Skeleton: The network is a frame structure; the bones themselves are solid; and the skull is a hollow, rounded object.

## 2. Form and Function

### 2.1. Form is the physical characteristics of a structure and what they are like on the outside.

2.1.1. The statue of Venus focuses more on form than function, because it was carved for its physical appearance rather than for a certain purpose.

2.1.2. This strange structure made of metal is an example of form. Like the statue of Venus, this structure was built for its form, and probably not for its function.

### 2.2. Function, the purpose/use of a structure, is one way of classifying structures.

2.2.1. This shopping cart was probably designed to meet its purpose. There is a space to put groceries in, and the metal rods are strong for heavy loads.

2.2.2. A water bottle like the one above is designed for function. It is leak-safe and made of plastic, making it light. Also, there is a tube down the middle to make srinking easy.

### 3.1. Static load is a load created by only gravity applied to a structure.

3.1.1. Live load is the term used to describe the load other that the structure itself that creates a static load on the structure; it is not constant.

3.1.1.1. When you have books on a desk, the books are applying gravity to the desk (structure). The books are not constant and they may be removed.

3.1.1.2. The people in the car are the live load, and are adding to the force of gravity acting on the car.

3.1.2. The dead load of a structure is the weight of the structure itself, which must withstand gravity and cannot be changed.

3.1.2.1. In this pencil case, the case itself, the constant, is the dead load; gravity is acting on it.

3.1.2.2. The image presented above shows the bed as the dead load; gravity pulls on the structure and the load cannot be removed from the structure.

### 3.2. Dynamic load is load that external forces other than gravity exerts on a structure.

3.2.1. A hurricane is an excellent example of dynamic loads; the wind is applying push to the trees, a different force than gravity. Also, the rain may be whipping the trees.

3.2.2. Dust Storms are also excellent examples of dynamic loads, since the sand, carried by the wind, is a force to the little house as it bounces along; and the wind itself is pushing at the structure.

## 4. External Forces

### 4.1. Other forces are external forces other than gravity, and can be classified as a push or a pull.

4.1.1. A push is the act of exerting a force to a structure which brings the structure away from the source of the force.

4.1.1.1. when you do a push up it is an push example. when you go down you are forcing yourself to push yourself up. you push yourself up so you do not fall on your stomach flat.

4.1.1.2. pushing a car is another example. when your car is tuck or when it is out of gas you have to push it. you force yourself to push the weight and get to move. that way you apply the pushing force.

4.1.2. A pull is the act of exerting a force to a structure which brings the structure towards the source of the force.

4.1.2.1. when you do chin ups it is another example of a pull force. you are forcing yourself to pull your body weight uptill where you have to touch the pole.

4.1.2.2. climbing something would be a pulling force example. say your climbing a steep mountain. you are using all your strength to climb the mountain. you are pulling yourself up so you can get to the high point.

### 4.2. Gravity is the force of the earth pulling objects/structures down; gravity also keeps things anchored to the earth.

4.2.1. Center of gravity is the center of all the mass in an object. Most/all of the weight is concentrated on this point. The center of gravity affects the stability of a structure. For example, in the image above, the woman has a lower center of gravity, while the man has a higher center of gravity. This means the woman is a more stable structure than the man.

4.2.1.1. One way to lower the center of gravity is by having a wider base and a narrower top. More of the weight is at the bottom, which means the center is closer to the bottom. This pyramid is a good example.

4.2.1.2. Another way to lower the center of gravity is by moving the mass. By putting most of the weight at the bottom, a low center of gravity is ensured. This house would be stabler if most of the heavy furniture were moved to the basement.

4.2.2. spilling glue is an example of gravity. when you are going to paste something on with glue it is an example. when you tilt the glue bottle you will see that gravity will pull it down and it will hit the paper.

4.2.3. when you jump the gravity will pull you down and you will hit the ground. if you jump from a high distance the gravity will act faster and pull you down and you will hit the ground harder

## 5. Internal Forces

### 5.1. Compression occurs when external forces push an object in opposite directions, causing the it to react by becoming smaller, sometimes bending.

5.1.1. Accordian

5.1.1.1. an accordion is an example of an compression force. you are pushing the object to make the sound of the accordion come out. the force is a compression and a pushing force. you are applying these two forces on each of the opposite sides of the object to make the object useful for what it does.

5.1.2. Squeezing out a sponge

5.1.2.1. you are applying the force by squeezing the object. since it is a sponge you are applying the compression force to it to make the water come out of the sponge. that's how we use the force compression in a sponge.

### 5.2. Torsion is the act of twisting an object in opposite directions.

5.2.1. Wringing out a towel

5.2.1.1. when you wring out the towel it is an example of a torsion force. you apply the force when you place your hands on each end and turn it in the opposite way. this is when you apply the torsion force.

5.2.2. twisting a cap to open the bottle

5.2.2.1. when you try to open a bottle cap you are applying the torsion force. you are placing your fingers on the cap and twisting the cap to open the bottles cap.

### 5.3. Tension is when external forces pull at an object in opposite directions; the object responds by becoming longer and narrower.

5.3.1. tug a war

5.3.1.1. you are applying the force by pulling the rope in opposite directions. you are trying to win by putting in all the force you can and trying to pull over the other team. so you are putting the force tension by pulling the rope in opposite directions to win the challenge.

5.3.2.1. you are applying the force tension by walking your dog. you are trying to pull on the rope so your dog doesn't run away and your dog is trying to run away. so you and your dog are pulling in the opposite directions and you both are applying forces on both ends.

### 5.4. Shear is caused by either pushing or pulling an object in opposite directions, which results specifically in the object tearing/splitting.

5.4.1. cutting things

5.4.1.1. scissors have the power to shear objects. especially paper. when you apply the force by pushing the scissors down it will cut the object. that will make it a shear example and will tear or split the object.

5.4.2. chopping a tree

5.4.2.1. when you chop the tree down you have to split it down. splitting is a example of tension. you are using an ax to chop the tree down and you are using all the force you can to split it in half

## 6. Applying Forces

### 6.1. Magnitude of force is how hard or light the force is being applied.

6.1.1. Typing is one way of using a light magnitude of force on a structure; the fingers often tap lightly on the keys on the keyboard.

6.1.2. A wrecking ball uses a hard/heavy magnitude of force; it swings hard to demolish a brick wall.

### 6.2. Point of Application is the area which the force is being applied to on a structure.

6.2.1. When hammering a nail, the force is applied to the top of the nail, where the force from the hammer is best used.

6.2.2. In this car crash, the car has crashed from the back, so less of the car is damaged, the back being its width.

### 6.3. Plane of application is the angle the external force is coming at.

6.3.1. For example, if this fist was coming to punch you, it would hit your face straight-on, or at a ninety-degree-angle.

6.3.2. In this picture, the pass between the two players would hit the receiver's stick at a sort of slanted angle, maybe 60 degrees.

### 6.4. Direction of force is the direction the external force is being applied to a structure.

6.4.1. Pushing a wheelbarrow is an example of push; the force is acting by bringing the object away from the source of the force.

6.4.2. Pulling a wagon is an example of pull; the force is acting by bringing the object towards the source of the force.