Understanding Stress and Strain

Understanding mechanics is nothing to do with mathematics, it is the reality of what is actually happening and why it is happening.

Stress and strain

A lot of confusion with these, even with engineers. Basically, stress can be considered in relation to a car spring. Once the spring is fitted to the car it is in a state of stress, but even after years of going over bumpy roads and constantly being in  a state of stress, if you take it off the car it should retain its original length. However, if its length has reduced, then strain has taken place.

Strain is damage caused by too much stress.

A stress fracture is a strain caused by too much stress.  The stress applied has exceeded the design stress of the bone structure.

A pulled ligament is a strain caused by too much stress. The stress applied has exceeded the design stress of the ligaments.

All mechanisms whether in engineering or biology are designed to operate within certain stress levels. As long as we stay within these ‘design’ parameters the mechanism should operate quite happily. If we exceed these parameters then strain is likely to occur.

Note that both strain and sprain have basically the same meaning.

Note: You would think that the people who made shock absorbers and dampers should know the difference. The shock absorbers on a car are the springs. What are sold to the public as ‘shock absorbers’ are in fact dampers, they dampen the oscillations that are created by the springs. Without the dampers your car would bounce along the road like a kangaroo. This is why DAMPERS are so important on a car. A spring absorbs the energy of a wheel passing over a bump in the road and temporarily stores it as stress in the spring. Immediately after passing over the bump the spring attempts  to release this stored energy as quickly as possible, (which would cause the car to bounce). The damper prevents this happening by slowing down the rate at which the stored energy is released. In biology numerous muscles are used to act as dampers, acting as controls to prevent excess body movements that would be dangerous or inconvenient.

The kangaroo utilises a good example of the same basic principles, its legs storing energy in the form of stress in the leg muscles, the stored energy being used to help to power its next jump.

Author – Brian Williams.

Understanding Speed & Velocity

Understanding mechanics is nothing to do with mathematics, it is the reality of what is actually happening and why it is happening.

Speed and velocity

In practice speed and velocity have exactly the same meaning. Speed comes from the  Anglo-Saxon/Dutch/German, and Velocity comes from Latin.  Both derivations mean speed in the sense that the public understand it. However the physics establishment has decreed that velocity now means speed in a particular direction.  Unfortunately, having confused the public with the change in meaning, they now appear to just as confused themselves, because they are constantly referring to  cases that are  clearly ‘speed’ and calling it velocity.

A typical situation is where they refer to the ‘velocity’ of a wheel. No point on a rotating wheel has velocity.  All points on a rotating wheel have speed.

Obviously the above statements only apply in a situation where the centre of rotation is fixed. If we consider the wheel of a car travelling at 50 feet/sec along a perfectly flat road then the velocity of the wheel is 50 feet/sec. This refers to velocity of the centre of the wheel. Ignoring the resilience of the tyre, the speed of the wheel’s outer edge is 50 feet per second. ( Due to the resilience of the tyre the speed must be greater than this). The outer edge of the wheel does not have any velocity because it is never travels in a straight line.

Note: Newton was aware of this problem when he created his calculus but the physicists ignored it, and used Leibniz’s version of the calculus instead, in fact Newton’s calculus is almost never used and the modern calculus is the simpler Leibniz version.

Although this may seem a minor point it does present major logic problems in understanding the mechanics of rotary motion. The mathematics of rotary motion work but are completely illogical regarding the reality of rotary motion. This was evident even in school when much protestation was made about the lack of logic in the maths. Eventually the teachers agreed with us but argued that as it worked we should ignore the logic.

Note the following statement attributed to Einstein

Understanding Momentum

Understanding mechanics is nothing to do with mathematics, it is the reality of what is actually happening and why it is happening.

Momentum

Momentum is the oldest scientific principle. Virtually all living creatures are both actively aware of it, and both consciously and unconsciously make use of it in their everyday lives.

Its use and the understanding of it preceded the emergence of man from the primeval chaos, and billions of years before the first glimmering of ‘scientific’ thought.

Consider a grizzly bear. It will give its young cub a gentle ‘pat’ of affection, or it will give a more vigorous smack to warn it to behave itself. Later, it may (with the same arm and paw) give a killing blow to an enemy.

The bear is demonstrating a clear knowledge and understanding of momentum. All animal life demonstrates this understanding, from the amoeba through to the dinosaurs, fish, reptiles etc and mankind, a very late starter.

This knowledge of momentum is gained very early in an animals life because its survival depends on it. It learns about it whilst attempting its first steps, because walking depends on control of momentum. Early on it constantly falls, but with practice it learns to control it and starts to walk with more confidence. The adult stage really begins when the animal can control its momentum and gains survival capabilities, not by the strength of its parents but with the speed and agility to escape danger.

So, what is momentum? It is not a mathematical formula. Momentum is the effect of mass and speed and is real. When someone refers to momentum being mass x speed this is a means of relating the reality of momentum into a mathematical context. Mathematics is not reality, and the reality of any subject should be constantly in your mind when manipulating mathematics.

Mathematics is not a science, it is a tool. In many cases maths does not work, or only works by cheating. A term constantly used in engineering is ‘Moment of Inertia, (and I must have used this myself a thousand times or more) which is used in bending and stress calculations, but is purely a fiddle factor and is used to make the maths work out. The square root of -1 is still argued about in physics calculations, yet it has no real meaning due to mathematicians incorrectly applying normal mathematical rules to graphs.

Millions of hours have been spent trying to out a ‘true’ value for Pi in relation to circles, without mathematicians understanding that it is an impossible task. Each step closer changes the parameters, which means that the numbers after the decimal point will go on forever. I have no doubt that somewhere in the universe there is a mathematical system that will solve many of our problems, but it will not be our current system.