Static Equilibrium

Static Equilibrium is the physical state in which all components of a system are at rest and the net force is equal to zero throughout the system. When a system is in static equilibrium, it means that all the components of the system are not accelerating as a result of the net force equaling zero. An example of a system in static equilibrium is a game of tug of war.

This system of forces is considered to be in static equilibrium because the force that is being applied by the first man is equal to the opposite force being applied by the second man. Therefore, the sum of the forces, or the net force of the system, equals zero. Since the forces are balanced, it also means that there will not be any acceleration of the rope in either direction.

In addition, another characteristic of a system of forces that is in static equilibrium is that the system also has zero torque. Torque is a measure of the turning force on an object. Torque can be thought of as a twist to an object. An example of a system of forces that seems like it should be in static equilibrium is this diagram because te forces are balanced. However, there is torque in the system, which will cause the system to rotate.

My Bridge

When constructing my bridge I plan to produce a relatively basic truss bridge. By studying other successful balsa wood bridges on balsabridge.com I have found that the best bridges utilize either a truss or a piece of circular bent wood acting as a different type of truss. I decided to go with a truss because I believe that it is a slightly more basic structure type to understand and that it will be easier to construct. I took how easy the bridge was to construct into consideration because I wanted to try to decrease the percentage of error of my bridge failing as much as I possibly could. The design of my bridge looks much like this design:

I feel like this design was one of the best designs for constructing a balsa wood bridge because this is a strong truss design which will distribute the force that is applied by the weight nicely. In addition, this truss design is one that does not have an upright beam that is located at the midpoint of the bridge. This makes this design one that can be used for this particular project because if it were to have that upright beam at the midpoint then the metal rod that suspends the weight would not be able to be placed there.

Bridges

A bridge is a structure built to span physical obstacles for the purpose of providing passage over the obstacle. Bridges may be classified by how the forces of tension, compression, bending, torsion and shear are distributed through their structure. Here are a few of the many structure types.


Beam Bridge: Beam bridges are the most basic of bridge structures. They are made up of horizontal beams that are supported at each end. The earliest of beam bridges were most likely logs laid out across rivers or other gaps.

Arch Bridge: An arch bridge is a bridge with abutments, or structures built to support lateral pressure on each end shaped as arches. Arch bridges work by transferring the weight of the bridge and its loads partially into a horizontal thrust restrained by the abutments at either side. The earliest known arch bridges were built by the Ancient Greeks.

Truss Bridge: A truss bridge is a bridge that utilizes a truss in its a structure. This truss is a structure of connected elements forming triangular units. The connected elements (typically straight) may be stressed from tension, compression, or sometimes both in response to dynamic loads. The truss bridge is one of the oldest structure types that are still commonly used today.

Suspension Bridge: Suspension bridges are suspended from cables. These cables are hung from towers that go very deep down into the ground. The earliest suspension bridges were made of ropes or vines covered with pieces of bamboo.

Robotics

Robotics is defined as the branch of technology that deals with the design, construction, operation, and application of robots. A robot is a machine that can perform complex actions automatically. Robotics also deals with the computer systems that have the capability to control the robots through programming. Mechanical engineering, electronic engineering, and computer science are all incorporated in robotics. The use of robotics has proved to be extremely helpful to humans over the past years because robots have been made that have the capability of performing important and or hazardous jobs. The programming (explained in the post titled "Programming,") of algorithms is what enables robots to perform the functions that they do. In order for these robots to function automatically, they must be fueled by a source of power. A few of the various sources of power that allow robots to work are batteries, hydraulics, and even complex power sources such as organic garbage (through anaerobic digestion). Robotics is an extremely intricate and complicated branch of technology that will surely be beneficial to humans as we discover more about it.

Programming

Computer programming is defined as the creating of a sequence of instructions that enables the computer to perform the desired action. When programming, it is necessary to understand and analyze what action or procedure is desired from the computer before beginning the actual program. In order to create a message that tells the computer what actions it should perform and that can be understood by the computer, an algorithm has to be created. An algorithm is more or less an illustration of logic written in software that expresses what actions the computer should perform in a logical order.

This is an example algorithm

Programming is not only used to tell computers to perform various actions, but also in robots. When building my robot with my group, we performed very basic programming by creating a very small algorithm. Our algorithm instructed our robot to perform very simple tasks. The most complex of which was to order the robot to continue to move until within a certain distance of a colored brick, and then to drag the brick as the robot moved backwards. In order to perform programming, one must possess a great amount of logic.

My Group's Robot

My group consisted of three students: Louise, Juiliette, and myself. My group attempted to build the "gyro boy," robot. However, we did not fully complete building the lego structure that would have made up our robot. Our group was most likely unable to finish building the robot as a result of our lack of experience in building legos in the past. A few errors were made in the construction of the robot that caused us to waste portions of our building time. In addition, our group also encountered difficulty when we attempted to program our robot in the beginning stages. This time of difficulty also accounted for time that could have been spent completing the robot. Although our group was not able to complete the robot I had fun working on this project and learned some of the basics of programming and robotics.

What my group's robot would have appeared like if it were fully completed. 

Mechanics Of Catapults

Catapult physics is basically the use of stored energy to hurl a projectile (the payload), without the use of an explosive. The three primary energy storage mechanisms are tension, torsion, and gravity.

Catapult Physics — The Mangonel 

The above picture of the mangonel is what people are most familiar with when they think of catapults.The mangonel consists of an arm with a bowl-shaped bucket attached to the end. In this bucket a payload is placed. Upon release, the arm rotates at a high speed and throws the payload out of the bucket, towards the target. The launch velocity of the payload is equal to the velocity of the arm at the bucket end. The launch angle of the payload is controlled by stopping the arm using a crossbar. This crossbar is positioned so as to stop the arm at the desired angle which results in the payload being launched out of the bucket at the desired launch angle. This crossbar can be padded to cushion the impact. 

The mangonel was best suited for launching projectiles at lower angles to the horizontal, which was useful for destroying walls, as opposed to the trebuchet which was well suited for launching projectiles over walls. 

However, the mangonel is not as energy efficient as the trebuchet for the main reason that the arm reaches a high speed during the launch. This means that a large percentage of the stored energy goes into accelerating the arm, which is energy wasted. This is unavoidable however, since the payload can only be launched at high speed if the arm is rotating at high speed. So the only way to waste as little energy as possible is to make the arm and bucket as light as possible, while still being strong enough to resist the forces experienced during launch. 

The catapult physics behind a mangonel is basically the use of an energy storage mechanism to rotate the arm. Unlike a trebuchet, this mechanism is more direct. It consists of either a tension device or a torsion device which is directly connected to the arm. 

Catapult Physics — The Trebuchet

Among the various types of catapults, the trebuchet was the most accurate and among the most efficient in terms of transferring the stored energy to the projectile. In addition, it allowed greater consistency in the throws due to the fact that the same amount of energy could be delivered every time, by way of a raised counterweight. 

A trebuchet works by using the energy of a falling (and hinged) counterweight to launch a projectile (the payload), using mechanical advantage to achieve a high launch speed. For maximum launch speed the counterweight must be much heavier than the payload, since this means that it will "fall" quickly. 

Source: http://www.real-world-physics-problems.com