Forces:
There are different types of forces in physics, always denoted as f (usually with a subscript). They are separated into two different categories- field and contact. Field forces are things like electromagnetism, but for this project, we don't look into how they effect our bridges. The other, contact, is our style. The affect a single point. These can also be called support forces, and include things like the normal force, which is the tension that holds up a surface, which deals with compression. more on that later.
Weight:
Weight is a pretty simple concept. In a mathematical model, it is the mass times the acceleration. In this case, since nothing is moving, it is always the mass times the acceleration due to gravity- 9.8m/sec^2. It is almost always thought to be "negative" in a simulation. In our project, weight was the only example of a shearing force, in which the load forces in a direct "slice", creating the shearing affect.
Equilibrium:
When talking about weight, another concept that comes up is equilibrium, which is when all the forces- the net force- equals 0N. An equilibrium exists when an object is static, has no motion, or when it is moving at a constant velocity, known as dynamic. This is a very useful tool to know when building bridges, because it allows us, as long as there is a non moving weight on the bridge, to know that as long as the bridge is still standing, the bridge has a total of 0N on it. In simple terms, the "negative" weight cancels out with the "positive" support forces of the bridge.
Torque:
Torque is force applied to a lever arm, or T=fl. the lever arm is always perpendicular to the surface on which the force is applied. For a bridge with uneven weight, this allows us to find how much force is on each side of the bridge.
Hooke's Law:
In having to do with how much force an object can take, you use Hooke's Law, known as f=Kx. Simply put, that is the force applied equals the change in position times its constant of elasticity. It is constant until a point, in which the material breaks or becomes deformed. We did not really use this here, but in bridge force diagrams, it is very useful. here is a pretty decent example:
Depending on where the load is one the bridge, the forces acting on the sides are different. This is turned into a lever arm, so hookes law can apply the distance the load is from the fulgrim and the amount of force on the lever into how much force is on each side. The forces on each side, regardless of if the bridge holds or not, will experince the force of the load.
Compression and Tension
Perhaps the most important thing that we saw was the difference between compression and tension. Compression is when two or more forces come together and push toward the center of and object. Tension is the opposite, as forces push towards the edges of the object. In dealing with bridges, these forces act at the same time on different parts of the materials, like so.
Moving on!
