Notes on Mechanical Devices for the Electronics Experimenter

Summary

I got this book because I don't know much about mechanical engineering and this seemed like a great intro.

The introduction says it's meant for amateur experimenters to get a good foundation for experimentation and measurement and build by designing<=>building<=>testing.

Perfect!

Ch 1: Basic mechanical principles

Fundamental Qualities

We need to define some fundamentals before getting to the interesting stuff. Let's power through it.

There's 3 fundamental qualities that makes up reality, physics-wise:

1. Length - was once defined by a metal rod. Now it's defined by the speed of light.

2. Time - Once defined by a fraction of a day in 1900. Now it's defined by periods of radiation from a cesium atom.

3. Mass/Weight - Mass is constant, but weight is "mass * the-acceleration-of-gravity". In any case, for us it's the same.

Notably, here's a few units of mass:

• kilogram - kg -- 2.204 pound-mass
• pound-mass - lbm -- 0.4536 kg
• slug - slug -- 32.174 pound-mass

Yes, we're just treating pounds as a mass by calling it pound-mass.

There's also these other relevant units of reality:

• Electric Current - force generated between two conductors at some length, measured in "ampere"
• Luminous Intensity - light-ness, measured in "candela"
• Temperature - measured in "kelvin" as well as F and C.

Vectors & Motion

How do measure how stuff moves across space (length) and time?

Vectors

Vectors show you force has a horizontal and vertical component. For example, if this slash "\" had an arrow pointing down, then if it were moving a box, that would push it both into the floor and across the floor. Woo hoo.

Motion

Here's some key things:

1. Speed / Velocity - distance over time

2. Rotational Speed - revolutions per minute or angular distance traveled (degrees per second, radians per minute)

3. Acceleration - the rate of change of velocity. So if acceleration is 0, then the velocity is constant. (d*sec^-2)

Force, Work, Power

Wow, I can't believe these common-sense definitions. So much clarity compared with high school:

1. Force - the tendency to cause motion, or rather to cause acceleration (this is like mass, an absolute unchanging thing) -- newton

2. Work - force as applied through a distance (this is like weight, force that becomes tangible in-action) -- force * distance

3. Power - the rate of doing work or producing energy. (this is like velocity, work over time) -- work/second

3.1 Torque - the turning effort of a wheel. (this is measured in the same stuff as power, but uses horsepower, watts, or foot-pounds*minute^-1)

Force makes sense because whenever you move something, you're causing it accelerate. And this is different from work, which is like "over how much distance (rather than how much time) was force applied? Force is a vector and work is more of an outcome.

Also what blows my mind is they have this picture of a box hanging by two suspension wires, where one is horizontal, and the other is on the right corner at a 30 degree angle upwards. The 3rd force is the vector of gravity. So based on how heavy gravity happens to be, it changes the amount of force exerted by the horizontal vector because the angled suspension wire also applies a force through that trigonometry cosine math.

work IS energy: foot-lbs is the same as joules, kilowatt-hours, newton-meters, ounce-inches. Just different forms of the same thing.

Consistent Units for F = ma

System | Force | Mass | Acceleration mks (SI) | newton (N) | kilogram (kg) | m * s^-2 cgs | dyne (dyn) | gram (g) | cm * s^-2 engineering | pound (lb) | slug | ft * s^-2

Friction

In real life, friction stops F = m*a from being totally true. There's 2 important types of friction and some related concepts:

• Force Max (of friction) - the amount of force necessary to move an object bc it is greater than the friction of Force Max
• Force Normal - the amount of force pushing an object in the floor
• Coefficient u Static - a multiplier that lets you show the relationship between Force Normal & Force Max such that F(max)= u(static)*F(normal)
• Force Friction - this is a changing amount, because there is less friction for an object already in motion
• Force Dynamic - the amount of friction force on a moving object
• Coefficient u Dynamic - same as Static, but for a moving object

Levers

Levers have 3 magical features:

• Change direction of force -- A downward force becomes an upward force. If you have a spring, an upward force becomes a downward force.
• Amplify force -- When the load is closer to the fulcrum than the effort is, then more force is applied to the load!
• Amplify motion -- When the effort is closer to the fulcrum than the load is, then the distance moved by the load is greater than the effort!!

Holy Shit!

There are 3 types of levers:

• where o is the load, x is the effort, and A is the fulcrum, and ______ is the arms of the lever, distinguished as a load arm and effort arm.
• where effort force is applied against the arms
• where load is lifted up in first, second, and third class levers

• First Class - classic

o______x

- - - A - - -

• Second Class - specializing in amplifying force, because the load is closer to the fulcrum than the effort, by definition!

________

A - - o - - x

• Third Class - specializing in amplifying motion, because the effort is closer to the fulcrum

________

A - - x - - o