OpenStem

@openstem · Joined Jul 2026

7420 public items8 groups

Note~330 words · 2 min

Archimedes' principle The upward push equals the weight of the fluid shoved out of the way. Float, sink, or hover The steel ship, resolved Worked: what a floating ship weighs Floating at rest means weight equals buoyant force. Displacing 5

Engineering

Engineering · L3 · Buoyancy & Archimedes' Principle

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Note~382 words · 2 min

One project, start to finish The design process makes most sense watched in action on something small. This follows a desk phone stand through every stage, including the part textbooks skip: what happens when the first prototype doesn't wor

Engineering

Engineering · L3 · Case Study: Designing a Phone Stand

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Note~280 words · 1 min

A design that doesn't fit the budget isn't a solution Performance isn't the only test. Whoever is paying has a fixed amount of money, and a brilliant design at twice the budget simply doesn't get built. Cost estimation predicts what a proje

Engineering

Engineering · L3 · Cost Estimation & Budgeting

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Note~276 words · 1 min

Shear vs normal stress Same units as any stress, pascals, though fastener work is usually quoted in MPa. Single vs double shear A shear plane is where two connected plates try to slide past each other across the fastener. Worked: a 10 mm bo

Engineering

Engineering · L3 · Shear Stress

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Note~227 words · 1 min

Two ways to fail in compression Buckling arrives at loads far below the crushing strength, and it arrives suddenly. Push a drinking straw end-on and you'll see it. Euler's critical load Length dominates, because it's squared Real ends aren'

Engineering

Engineering · L3 · Column Buckling

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Note~441 words · 2 min

What actually reverses The instantaneous voltage V_peak is the highest the wave ever reaches; ω is angular frequency in radians per second. One cycle sweeps 2π radians, so multiplying cycles per second by 2π converts f into ω. The curve ris

Engineering

Engineering · L3 · AC Circuits Basics

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Note~406 words · 2 min

A switch flipped by electricity A transistor is a three-terminal device that acts as a switch, except the thing doing the switching is a small current instead of a finger. That one idea is why every processor, microcontroller and motor driv

Engineering

Engineering · L3 · Transistors as Switches

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Note~330 words · 2 min

Viscosity is internal friction It's a fluid's resistance to being sheared as it moves. Honey resists a lot and pours in a thick ribbon; water resists little and splashes. Every fluid has some, including air. Two flow regimes The Reynolds nu

Engineering

Engineering · L3 · Viscosity & Flow Regimes

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Note~332 words · 2 min

Moving heat without mixing fluids A heat exchanger passes heat from a hot stream to a cold one through a thin metal wall, usually a bundle of tubes. The wall conducts well and keeps the fluids apart. That separation is the point. The two fl

Engineering

Engineering · L3 · Heat Exchangers

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Note~408 words · 2 min

Find the failures on paper first FMEA is a systematic way to list how something could fail, rate each way by risk, and fix the worst ones during design rather than after customers find them. A failure mode is one specific way something goes

Engineering

Engineering · L3 · Failure Mode and Effects Analysis

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Note~500 words · 3 min

The public can't check your work People crossing a bridge or plugging in an appliance never inspect the engineering behind it. They can't. That's why the profession asks its members to hold a standard above "met the letter of the contract",

Engineering

Engineering · L3 · Ethics and Professional Responsibility

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Note~547 words · 3 min

Failure without ever overloading anything Until now, failure meant one load big enough to break something. Fatigue is different: load and unload a part repeatedly at a stress that would never break it once, and it breaks anyway. Each cycle

Engineering

Engineering · L3 · Fatigue & Cyclic Loading

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Note~389 words · 2 min

From matching properties to measuring them Earlier material selection was qualitative: a cable needs strength, a diving board needs flex, a drill bit needs hardness. Useful as a first filter, but it puts no number on how much better one opt

Engineering

Engineering · L3 · Strength-to-Weight Material Selection

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Note~221 words · 1 min

Two resistors, one tap point Worked values What it's actually for The assumption that bites people The formula assumes almost no current leaves the tap.

Engineering

Engineering · L3 · Voltage Dividers

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Note~262 words · 1 min

Collapse the network to one number Replace a group of resistors with the single Req that would draw exactly the same current from the source. How you combine them depends on the wiring, and nothing else. Series: resistances add Chained end

Engineering

Engineering · L3 · Equivalent Resistance: Series & Parallel Networks

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Note~461 words · 2 min

Head is pressure, expressed as a height A pump raises a fluid's pressure, but pascals are hard to picture. Head restates that pressure as the height of fluid column it could support. A pump adding 98,000 Pa to water gives H = 98000 ÷ (1000

Engineering

Engineering · L3 · Pumps, Head, and Matching a Pump to a Job

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Note~370 words · 2 min

Putting a number on "good insulator" Insulation resists heat flow. But "resists heat" is useless for sizing a furnace or checking a building code. R-value is the number: higher R means a given thickness resists heat flow better. Bigger area

Engineering

Engineering · L3 · R-Value & Thermal Resistance

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Note~414 words · 2 min

Break the project into tasks A task has to be small enough that you can estimate a duration and say clearly when it's finished. "Build the treehouse" can't be scheduled. "Cut the wood to size" can. Each task then needs a duration, based on

Engineering

Engineering · L3 · Project Scheduling

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Note~394 words · 2 min

Designing for how it'll actually be made A part can be perfect on the CAD screen (right shape, right strength, every dimension to spec) and still be a nightmare to manufacture. DFM is designing so a part is easy, fast and cheap to produce,

Engineering

Engineering · L3 · Design for Manufacturing

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Note~473 words · 2 min

The workhorse of industrial feedback control. One error signal, three ways of reacting to it. The error is e(t) = setpoint − measured output. Everything below acts on that. Effect of each gain Ziegler-Nichols tuning (ultimate gain method) A

Engineering

Engineering · L4 · PID control: tuning, anti-windup, and practical design

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Note~565 words · 3 min

Force in, deformation out, and the point where the part stops coming back. That's the whole subject. Bridges, aircraft, pressure vessels, implants, microchips: all of them are this calculation, done carefully. Stress and strain tensors The

Engineering

Engineering · L4 · Stress, strain, and material failure: from Hooke's law to fracture mechanics

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Note~515 words · 3 min

Fluid mechanics covers flow in pipes and ducts (internal) and flow over aircraft and ships (external). Three splits decide which equations you're allowed to use. The three conservation laws Sizing a pipe run, start to finish Laminar flow: H

Engineering

Engineering · L4 · Fluid mechanics: pipe flow, boundary layers, and dimensional analysis

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Note~601 words · 3 min

Material choice is one of the first decisions in a design and one of the hardest to reverse. It sets weight, cost, strength, thermal behaviour, corrosion life, how you can make it, and what happens to it afterwards. The four classes at a gl

Engineering

Engineering · L4 · Engineering materials: metals, polymers, ceramics, and composites

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Note~509 words · 3 min

Two forces come out of air moving past a shape: lift, perpendicular to the flow, and drag, along it and opposing you. Angle of attack and stall α is the angle between the oncoming flow and the chord line. It's the pilot's main lever on lift

Engineering

Engineering · L4 · Aerodynamics: lift, drag, and airfoil behaviour

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Note~447 words · 2 min

Every design eventually has to be made. Which process, what tolerances, how features are dimensioned: those choices set cost, lead time, and whether the part works once it's in the assembly. Four routes from stock to part Choosing one Weigh

Engineering

Engineering · L4 · Manufacturing processes and GD&T: from raw stock to a functioning part

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Note~498 words · 2 min

Power engineering is the layer between a circuit diagram and the physical world: stepping energy up for transmission, delivering it as three-phase, and turning it into motion. Transformers Voltage scales with the turns ratio, current scales

Engineering

Engineering · L4 · Electrical machines and power systems: transformers, three-phase, and motors

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Note~469 words · 2 min

One set of rules covers amplifiers, suspensions, radios, and equalisers. LTI systems and convolution One measurement describes an LTI system completely: its impulse response h(t). The same picture, with a sum instead of an integral, is exac

Engineering

Engineering · L4 · Signals and systems: convolution, Fourier transforms, and digital filters

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Note~416 words · 2 min

A car suspension, a building floor, a turbine blade, a phone speaker: all of them start as one mass on one spring with one damper. Get that model's behaviour into your bones and the rest of vibration analysis is bookkeeping. Free vibration

Engineering

Engineering · L4 · Mechanical vibrations: natural frequency, damping, and resonance

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Note~323 words · 2 min

Strong form: what you'd like to solve That's the classical statement, and it demands u ∈ C². Two continuous derivatives everywhere, which is more than most real solutions have and far more than any piecewise-linear approximation can offer.

Engineering

Engineering · L5 · FEM: From Strong Form to Ku = f

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Note~376 words · 2 min

Equilibria, and what linearising tells you For an autonomous system ẋ = f(x), an equilibrium x* is any point where f(x*) = 0. Linearise there by taking the Jacobian A = Df(x*) and read the eigenvalues. Lyapunov's direct method You can settl

Engineering

Engineering · L5 · Nonlinear Dynamics: Lyapunov Stability & Bifurcations

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