Basic Physics Problems

This site has some models and software that should help you. At least you can get the equations from it.

http://www.analyticcycling.com/

-Matt

Ideologue said:

I am designing a bike, from scratch, and I would like to do it scientifically. I also want to use my bike design, complete with as much science as possible, as an entry method into a mechanical engineering course. The problem is I have not studied, or used, even basic physics equations for ages and I have not much time before I will have to submit the project to the admissions tutor, so I have not enough time to learn in the more orthodox way!

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Sounds like a great project good luck.

Bikeforums.net has a section devoted to frame building.

bikeforums.netforumdisplay.phpOpen ↗

mattjf said:

This site has some models and software that should help you. At least you can get the equations from it.

http://www.analyticcycling.com/

-Matt

Thanks for the link. I am still looking through that site, but the answers I seek do not, so far, seem to be all that easy to extract from it.

lwedge said:

Sounds like a great project good luck.

Bikeforums.net has a section devoted to frame building.

bikeforums.netforumdisplay.phpOpen ↗

Thanks for that. I registered with them a while ago. I was may post my questions there also; I will see how things go first.

I have a Mechanical Engineering degree (from Univ. of IL at Urbana - Champaign), I took A.P. Physics in High school, and I even competed to State JETS physics competition and our team got 3rd place in state. But to answer your questions I'd have to review my physics because I have never touched problems like these ever since I graduated school in 1992.

I also have the software to design a bike in 3d and doing physics modeling of it by computer. I have Solidworks 2006 with COSMOS and I have Pro Engineer Wildfire 2.0 with Pro Mechanica -- the two most widely used engineering programs.

Sorry I don't have time to help you, I'm too busy looking for a job and night school. A good physics book might help you.

I'm "rusty" with my engineering and physics now.

JTE83 said:

A good physics book might help you.

I have a few; I borrowed more from the library today. But none of them are as clear as I need them to be. I too have not spent much time at all on this subject since school and as a result I am struggling at the moment. The books I have need to be studied cover to cover in order to get a grasp on the subject. I am unable to do that at the moment as time is an issue and I need to submit this project very soon. Ideally I should have submitted it already.

Ideologue said:

I am designing a bike, from scratch, and I would like to do it scientifically. I also want to use my bike design, complete with as much science as possible, as an entry method into a mechanical engineering course.

Okay, so you want to create a perfect bike, from scratch, as an entry just to get into an engineering course, and you want the basics to be fleshed out for you by a bunch of guys on a bicycle bulletin board?

Thylacine said:

Okay, so you want to create a perfect bike, from scratch, as an entry just to get into an engineering course, and you want the basics to be fleshed out for you by a bunch of guys on a bicycle bulletin board?

Is that a bit of attitude I detect in you?

I have been designing this bike for three years now. When I started I knew nothing about bicycle geometry; I had to learn nearly everything from the beginning. I only started to design this bike as what I want is not produced by anyone else. Only within the past few months did I decide to enrole on a mechanical engineering course.

I am not making this bike as an entry method into a course. I was making it anyway. I mentioned it to the admissions tutor in an e-mail and was told if I can show adequate use of science, etc., then they would give me a place on the course. So I am starting from the basics, with the fundamental basic physics. I am now intending to be scientific all the way through to the conclusion of this project. Previously I was going by instinct, prior knowledge and on what other people are doing.

Requesting a little help on the basics of a subject that most people did at school (me too, but I have forgotten most of it), that many people know about, that is particularly relevant to cyclists and indeed is the fundamental information behind making things (anything!) I think is a reasonable request.

Are you able to contribute any answers?

I'm not entirely sure you understand the questions you're asking. For example in your inclined plane section the force required to go up the hill at 15 and 25 mph is the same, but the power requirement is dependent on the rate at which work is being done. Acceleration has several components in this case; tangential, vertical, and rotational. You can look at forces, but they still need to be resolved in time to have any meaning.

If you want to do this scientifically, you need to back off of the specifics and figure out what is the big picture question that you want to ask. Mashing together a bunch of equations (most of which you can find here: http://scienceworld.wolfram.com/physics/) is just going to waste time if you don't know where you're headed.

artmichalek said:

I'm not entirely sure you understand the questions you're asking. For example in your inclined plane section the force required to go up the hill at 15 and 25 mph is the same, but the power requirement is dependent on the rate at which work is being done. Acceleration has several components in this case; tangential, vertical, and rotational. You can look at forces, but they still need to be resolved in time to have any meaning.

If you want to do this scientifically, you need to back off of the specifics and figure out what is the big picture question that you want to ask. Mashing together a bunch of equations (most of which you can find here: http://scienceworld.wolfram.com/physics/) is just going to waste time if you don't know where you're headed.

Thanks for your post and apologies for my delay in replying. I understand what I want to know, but I have gone somewhat blank concerning the subject of physics at the moment! I am not trying to mash several equations together; what I will do, after figuring out each one, is add the forces together so I know how much power is needed and also work out torque figures and then how much metal has to be in the main drive shaft, etc.

Thanks for the link, it looks rather promising.

Ideologue said:

Thanks for your post and apologies for my delay in replying. I understand what I want to know, but I have gone somewhat blank concerning the subject of physics at the moment! I am not trying to mash several equations together; what I will do, after figuring out each one, is add the forces together so I know how much power is needed and also work out torque figures and then how much metal has to be in the main drive shaft, etc.

Thanks for the link, it looks rather promising.

That's a good start, but it's a bit backwards. The downside of human powered vehicle design is that it doesn't matter how much power you need, only how much you have. For vehicle performance calculations you want to build up an energy balance equation with your somewhat known power input on one side and work out the resulting speed/acceleration, or if you integrate over time your performance over a given course. The result however is going to be a shade better than useless. Of more practical use is the gradient of the energy function. Starting with a set of baseline parameters you can do a sensitivity analysis and get an idea of the relative merits of different design decisions. (speaking of baseline parameters and back to one of your original questions, a typical racing bike is around Ad=0.36m^2 and Cd=0.88 with the power[W] requirement being (1/2)rho*Ad*Cd*V^3. rho being air density[kg/m^3] and V[m/s] being velocity)
The plus side to having a more or less fixed power input is that the static and dynamic load ranges that you need to size your frame and drivetrain are completely unrelated to the actual performance of the vehicle.