My Bridge

My Bridge

In order to construct a bridge that will be able to support a mass well over fifty times its own, a balsa wood bridge must be carefully crafted with supports in order to dissipate force throughout the bridge, not just in the middle sector where the two-by-four will rest. In order to do that, the bridge that I am building will have trusses, or framework that supports a bridge or other structure, that will equalize the tension created by the weights. The trusses dissipate the force so that the bridge shares the force equally, so it does not bend and break such as under this beam bridge.

The weight of the elephant causes tension on the bottom of the bridge, with the bridge trying to support the weight. But without trusses, the part of the bridge where the elephant is would not be able to support that weight and it would eventually break. 

This is a picture of the way forces dissipate in a truss bridge, such as the one I am constructing. The forces now can be shared throughout the entire bridge.

This is a basic design of the bridge that I am constructing. The tresses and abutments on the ends help equalize the forces so that the bridge does not bend and break as easily under high amounts of pressure.

Static Equilibrium

Static Equilibrium

When all forces on an object are balanced, then an object is said to be in a state of equilibrium. Objects that are in a state of equilibrium must have an acceleration of 0 M/S/S. This does not necessarily mean that the object is at rest, though. An object could be moving at a constant 75 MPH but still be in a state of equilibrium as it is not accelerating. This derives from Newton's first law, or: 

•  An object is in rest and stays at rest, or
• An object is in motion and stays in motion with constant speed and direction

If an object is at rest and in a state of equilibrium, then the object would be in a state of "static equilibrium" with static meaning stationary or at rest. Bridges use static equilibrium to balance their forces. Structures on the ends of bridges, or abutments, help equalize the forces on the bridge so that the bridge does not collapse. In an arched bridge, the abutments at the end of the arch take the brute of the force and help dissipate it throughout the bridge. Some bridges such as suspension bridges try to dissipate it through the ground with the help of anchorages, towers, and cables.  

Forces at work in an arched bridge.

Another example of static equilibrium are balancing toy birds. The birds have weights in their wings and beaks that help the forces spread out and balance. This helps them reach static equilibrium and helps them balance on almost all surfaces.

 

Bridges

Bridges

Bridges are structures that span over some sort of obstacle such as a body of water, a trench, or a valley in order to provide transportation over said obstacle. Certain bridges must be able to withstand certain conditions such as the terrain or weather in which the bridge is anchored. For instance, in San Francisco, bridges must be able to withstand the frequent earthquakes that occur as the city is placed on a major fault line.

The Golden Gate Bridge in San Francisco

There are many different types of bridges that have spanned throughout history such as the beam, truss, arch, suspension, and many others.

Beam Bridge

The beam bridge is constructed of horizontal beams which are supported by structures at each end. These components support the downward weight of the bridge and any traffic traveling upon it. In supporting weight though, the bridge endures compressional and tensional stress. To try and spread out the forces, sometimes a longer beam is used. Sometimes the pressure is too much though and a truss may need to be used.

These are both examples of beam bridges.

Truss Bridges

A truss bridge is a bridge whos lattice-like superstructure that bears the load of the force. The support truss adds rigidity to the structure, greatly increasing its ability to dissipate the compression and tension caused by weight on the bridge. Once the beam begins to compress, the force is spread through the truss. 

Arch Bridge

The arch bridge has been used for over 2,000 years. Its elegant structure is composed mainly of two abutments, or structures at the end of the bridge where the superstructure mainly rests, at the end of each side of the arch that take the main amount of force. The curve of the arch and abutments greatly dissipates the amount of tension on the underside of the bridge. 

The second picture shows how the tension dissipates throughout the bridge.

Suspension Bridge

Suspension bridges suspend the roadway in between two towers held by cables. The towers support much of the weight as weight pushes down on the roadway, is transferred to the cables and then to the towers. The towers then dissipate the force directly into the earth. The cables however, receive most of the bridges' tensional force. The cables are attatched to anchorages, or large slabs of rock or concrete in which the bridge is anchored to, and the tensional force travels through the cables, to the anchorages, and then is dissipated into the ground.

Bridges come in all shapes and sizes, but they all basically do the same job: support weight over a certain obstacle. In order to do that job, they must find a way to dissipate the forces so that they do not buckle and break.

Programming

While building our group's Lego robot, the robot had to be programmed in order for it to know how to do certain tasks. The programming was relatively simple, as most of the tasks were already pre-programmed in the 'intelligent brick.' The user simply had to tell the software the order in which to do these tasks. Depending on the purpose of the robot, the brick could be programmed to follow certain instructions, either put in manually on the brick, or inputted on the computer and then downloaded onto the brick. The tasks could be changed depending on time variations, visual/UV sensor choice, and motion variations.

Programming Software on a computer

'Intelligent Brick' and its various buttons and functions

Lego Robotics

A robot is a mechanical or visual mechanism guided by computer software or electronic circuitry. Lego robotics is a way of building a basic robot (out of Legos, obviously) and being able to program it using their easy to use programming software, named an 'intelligent brick.' The robots run on battery that is charged using an outlet on the wall. Lego robots are fully functional, and instructions are included for many robots including the Puppy, Color Sorter, and Gyro Boy. In the world of science, robots are used for many things. They are used in factories, to build cars and electronics. They can also be used for the military, in schools, and in space. Robots are often used for jobs that are either harmful, unrealistic, or unattractive for humans, such as diffusing a bomb, fixing a part on a remote space station, or even picking up trash. Modern robots can be used for functional uses, and many depend on them for every day uses.

The Color Sorter

My group, consisting of myself, Luke and Amechi, built a color sorter for our group's final robot. The color sorter used visual technology to sense which color was being shown and temporarily saved it into the software. When the color block is placed in the slide, the robot remembers the order in which the colors were placed and moves along the tracks in order to place the colors in their own respective cups. The color sorter takes advantage of the visual sensor in order to sort colors with no regard to which order they are placed in.

Parts of the Robot:
-Tracks: Moves robotic slide across tracks
-Slide: Place where the colored blocks are placed after placing them above the visual sensor
-Robot: Place where programming happens and visual sensor is placed

Catapults

How Catapults Work

A catapult is a device in which tension is accumulated and then suddenly released in order to hurl a projectile. The device works entirely on the collection of potential energy in the form of tension. Potential energy is the energy of a particle, or system, due to position or condition rather than motion. The potential energy is stored when the arm is brought back and tension increased. When the arm is released and then quickly brought to an abrupt stop, the projectile retains the kinetic energy from the motion of the arm and is launched at the target. 

Newton's First Law

Newton's First Law helps us explain the launch of projectiles using catapults. Newton's First Law states that an object in motion tends to remain in motion unless acted upon by an outside force, so when the arm is stopped but not the projectile, the projectile keeps moving forward. The projectile eventually falls to the ground because of gravity, or the "outside force" in this situation. If we were in outer space, where there is no gravity, the projectile would keep on moving forever.

The Importance of Angles

When the tension from the spring or wire is released, the projectile goes flying. Let's say that x is horizontal velocity and y is vertical velocity. In order to gain maximum velocity in both x and y, I released my projectile at a 45 degree angle. Simple trigonometry tells us that when the sine or cosine of an angle is taken, the angle in which both the sines and cosines are equal is the 45 degree angle. Therefore, if released at a 45 degree angle, the projectile would have the exact same velocity in x as in y. This makes sure that it does not go too far upwards so that it does not get a lot of displacement in x, but also does not get so little displacement in y that it does not go far. If the figure below had had a 45 degree angle, then the velocities in x and y would've been equal. 

Mousetrap Catapults

Mousetrap catapults use the tension collected from the spring in order to snap abruptly and swing forward. When a bar of some sort stops the arm's forward motion, the projectile keeps moving forward using the kinetic motion from the arm. This rapid snapping motion from the mousetrap arm causes the projectile to be launched forward quickly.