DrD

Where did you get this force expression? Did you check the derivation? DrD

You have a rather difficult problem. The span of 278 m is quite long if you don't accept intermediate supports. Your bridge will be rather expensive to build because it will have to be very strong to support this length. DrD

Do you have a specific purpose in mind for this brush? That will guide many of your choices, and it is essential to giving you much help. Tell us more. DrD

In saying that you are a student, I presume this means that you are enrolled in a college. Your school will guide your program of studies. In general, you need a lot of math and physics. Good luck. DrD

I agree with most of what GB Reid has said. Brittleness is certainly the tendency to fracture rather than deform under load. I would disagree with the example of glass, however. It is my understanding that glass is actually a supercooled fluid ( although materials is not really my area). DrD

Sure looks like school work. I think I'll pass. DrD

Much depends upon what loads act to prevent this motion and also on the positional accuracy required. Have you considered something like a hydraulic or pneumatic cylinder? What about a screw drive? DrD

The simple answer is "yes, there is evidently something wrong with your calculations." Now you will probably ask what is wrong. That is harder. Where did you get the data for your calculations? What do you think you are calculating? To just through out a bunch of numbers with no statement of your approach to the problem is pretty meaningless. DrD

Have you downloaded a copy of my Theory of Machines text available at this web site? If not, I suggest you might want to do so. While this problem is not given there, a lot of similar things are discussed. Take a look. DrD

Well, I got one good comment from JAG. I presume that means that he and I are the only folks left who don't know everything. I suppose that stands to reason; we are both old men! I had no idea the rest of you were so brilliant and over-informed! To answer JAG's question, "What drives the design?" let me respond by saying "many factors." We might consider -- * cost and availability of materials (steel, concrete, stone, etc); * cost and availability of a work force familiar with construction in various materials; * cost and availability of machines to fabricate and erect the various bridge types; * local and national laws and ordinances regarding height of structures, visibility blockage ("must not interfere with airport approach," "don't block the view of the mountain or the lake"); * past experience of each designer/erector (some have never worked in steel but have lots of experience in concrete and vice versa); * opinions on aesthetics of various bridge types (suspension bridges look graceful, etc), There are probably some more factors, but this is a start. DrD

What Would You Like to Know? If you could ask me any question you want, what would you like to know that you think I might know? I certainly do not know everything, but through the years I have accumulated a certan amount of knowledge that I'd like to pass on to you. Therefore, I ask, what would you like to know? Many readers are still in college, and no doubt they would like to know what is going to be on the next exam. I'm sorry, but I have no way to know that. What I might be able to tell you is some examples of where your present studies might be useful in the future. I recall my own student days, and I often wondered, "Where am I going to need to know xxxx?" I simply could not imagine where xxxx might arise in the future. Other readers are out of college and in the industrial workplace. Some are doing fine with the knowledge they acquired in school, but others are discovering that they need knowledge and skills that were not taught in college. I know that this certainly happened to me. When I went out into industry, there were all sorts of problems that had never been mentioned in my college days and presented me with new learning challenges. That is a part of being an engineer; your whole career is a learning experience. At the same time, there are many situations where you might like to ask someone with more experience about a particular topic. So, I repeat, "What would you like to know?" Please comment on this blog post and give me your thoughts. DrD

Look up the definitions, and you will have your answer. DrD

If you are looking for steady operating power, the SumTorq = I * alpha does not help. In steady operation, all of the power input must be converted to heat. Where is it going? What are the torques that act on the system in steady state? Perhaps some viscous drag? Is there a brake? Is there a friction rub? Find these and figure out how much power they consume at operating speed. That is the required input power.

In what context? For what purpose are there benefits? DrD

The notches at the ends of the slot look like stress concentration factor relief. The small rib on the side wall can't be that at all. They may all be artifacts of the extrusion process that forms the section. DrD