Department of Good Engineering - Faculty of Life

Q: Why couldn't the bicycle stand up on its own? A: It was two tired.

2011-10-30T22:37:00.000-07:00

Do you know how to ride a bicycle and do not know why you can do it? A widely accepted theory behind bicycle stability is the gyroscopic effect. David E. H. Jones went on a journey to find out the truth. In his paper “The stability of the bicycle” published in 1970, he proved that gyroscopic effect is not the only ingredient to the magic. Here he is on the experimental bike with a counter rotating wheel:

David E. H. Jones on his experimental bike

He added an extra counter-rotating front wheel to cancel the gyroscopic effect and according to him the bicycle stayed stable even at lower feels. The only difference was that it felt a bit strange riding it due to a large moment of inertia about the front forks.

So what makes a bicycle going without falling over? “On the stability of a bicycle on rollers” by P.A.Cleary and P.Mohazzabi does an excellent job of summarizing the “Trail” effect that contributes to the stability of a bicycle. Considering the following figures from “On the stability of a bicycle on rollers”:

Figure 1, negative trail


Figure 2, positive trail

Imagine you are riding a bicycle with its front wheel configured like in Figure 2. Now imagine leaning to your right. Can you picture what would happen to the wheel? Remember that the wheel can only rotate about the steering axis. So if you were leaning on the right, the ground will push your wheel to the right about the steering axis i.e. the wheel turns with the right lean of the bicycle. How does this help in stability? It lowers the center of gravity which adds stability. If you also add centrifugal force acting on you when making a right turn/lean, the bike is being pushed to left while the ground forces the wheel into your turn or lean. This is what gives you the confidence when going around a corner on your bicycle, centrifugal force and the trail.

Now imagine you are riding a bicycle with its front wheel configured like in Figure 1. Imagine leaning to your right. And as we know the wheel can only rotate about its steering axis, the point of contact with the ground will push the wheel to the left when you want to lean to the right; ladies and gentleman, this is a recipe of a face plant.

I hope now you know what it takes to ride a bike: a positive trail, centrifugal force from god, and a helmet.

Trains can not go around a corner!!

2011-09-19T20:58:00.000-07:00

Of course trains can go around a corner! we will find out how in a bit. Previously I posted a video about car differentials. Why do we need a car differential? to allow the car to go around a corner i.e. during a turn let the outer wheel rotate more than the inside wheel.

BUT how about trains? how do they go around a corner? The answer is NOT a differential, ever look closely at a train axle? Its a solid shaft going through the two wheels. There is no differential in between like your car. The simple yet not so intuitive secret is the slightly coned shaped wheels.Watch the Richard Feynman interview and you will know why coned shaped wheels work.

If we love cars how come we didn't know this?

2011-09-18T14:45:00.000-07:00

Majority of students in my 3rd year mechanical engineering class asked this question, we all started doubting our love for cars. Prof. Cleghorn showed this video in class and this was the best tutorial a class had ever seen. If you drive a car or have a slightest hint of love for it you owe it to yourself to watch this video

Toilet Flush!

2011-09-18T10:57:00.000-07:00

Yes, a toilet flush. You are lying if you have never wondered how that water gets sucked down the drain! . If you are still wondering about it, lets fix it now. Before we go into the toilet flush, no pun intended, first discuss a physical phenomenon called siphon. This is an excellent video that demonstrates siphoning

In this video you saw:

1) Two cups, one filled with liquid and placed at higher elevation than the second empty cup

2) A straw inserted into the full cup with air pushed out of the straw creating vacuum inside.

3) Air pressure acting above the liquid in the full cup pushes water into the "empty" straw

4) Liquid flows into the second cup by act of gravity and higher pressure on the elevated cup (pressure difference = difference in height)

5) Liquid stops flowing when both cups have the same level of fluid i.e. no differential pressure acting on either cups (remember, pressure difference = difference in height)

Now, watch this video.

What you saw here is essential a siphon action.

1) Large amount of water flows in the toilet tank

2) Water pushes water over the "humped" pipe

3) Water traveling over the "hump" pulls all the water with it due to gravity

4) When all the water has drained, air enters the toilet bowel and you hear a satisfying gargle sound

So, a toilet only depends on large amounts of water going over the hump and gravity doing the rest. If you are still in disbelief, try pouring a pale of water in your toilet bowl

Good Engineering? Faculty of Life?

2011-09-18T10:26:00.000-07:00

Did you learn how to ride a bike and don't know how you did it? I asked this question a few years ago and now as a growing engineer I am seeing answers to this and many other questions. I expect that you may be wondering about the blog title "department of good engineering-faculty of life". My expectation arise from my own wonder about the relationship between nature and life. To me nature is the "good engineering" that shapes a life of everything from a particle to a mountain. To understand the nature, her laws and her acts of wonder is the satisfaction we all sometimes seek and indeed “the noblest pleasure is the joy of understanding”, Leonardo da Vinci. So if you are interested in getting to know about my hunt for answers and perhaps sharing yours, stay tuned!