Statics: Introduction

Statics is a part of what's called mechanics, and has  part of doing the physical nature of what things do. We're mostly going to do old stuff in new ways, so that we can do more realistic problems, and we're stepping towards realism towards the engineering career, and takes a couple ways to work up to realist.

Statics and Dynamics make a super advanced Physics I on steroids, which is Mechanics: heavier. You're going to need differential equations the next term. Other parts to this is also fluid mechanics, strength of materials coming out of statics, which can combine them into one 4-hour class. 

Statics, we're going to sum all the foreces acting on an object which will tell use how an object of a particular mass where there is no acceleration. If the acceleration is 0, then the velocity is constant. Everything we do in the class is constant, so we'll sum the forces, and set the sum equal to 0, and allow us to find the forces. We're going to force that condition on the problem, and make us figure out the unknowns in the real problems. We're going to look at structures, bridges, and trusses, that you don't want to accelerate. You don't want your name in the news as the engineer that designed the bridge that accelerated. Dynamics is when forces don't sum to 0 if there is some residual acceleration. 

We have to know enough equations for the unknown weights inside of the free-body diagrams. Again weight and mass are related that w = mg. Let's just keep things straightforward, and we have the weight if we know the mass, just w = mg is so obvious that we don't need to worry about what is asked for. w = mg always the only things that can change a bit is what is g but for the most part we deal with g as 9.81m/s^2 and we can solve the problem summing the forces equal to zero. There's only up and down problams and we don't need to deal with horizontal problems or forces. Since all of the forces sum to 0, then we can say that all of the up forces must equal all of the down forces in magnitude. 

The mass is not the force, it's the weight that's the force. Sometimes, you may need a greater mass than what's going to be in the problem. We will in strength of materials, that m = 122kg is not the mass we want to hang on, let's say there's screwing up manufacturing, etc. You NEVER want to design right to the limit in real engineering problems. We should use a factor of safety of around 2 to double the margin to prevent failure. The calculation say 122kg but recommend to the boss that "Don't go over 60kg". The factor of safety is VERY important in mechanics of materials. 

There is no negative g, g is always positive. The English unit is known as a SLUG. Forces in the English System are pounds, or pound force for the unit for force and pounds mass as the units of mass. The reason is because in the English System, the pound force was defined, and seperately the pound-mass was defined. 

The fewer steps, the fewer changes for goofing up, so we'll try to avoid places to goof up. That's the first section in the nutshell. Now let's step back and we need to very carefully make sure we can sum these forces right, so let's go over the trigonometry again. Remember the Forces just sum to some result. All vectors have 3 things, and they are magnitude, direction, and units.