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OpenStem
@openstem · Joined Jul 2026
7420 public items8 groups
Flashcards9 cards
How do you find the equivalent resistance of resistors connected in parallel?1 / 9
1/Req = 1/R1 + 1/R2 + 1/R3 + ... — add the reciprocals of each resistance, then take the reciprocal of that sum.
Engineering · L3 · Parallel Resistor Networks
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Engineering · L3 · Parallel Resistor NetworksFlashcards10 cards
What does a pump's "head" mean, in plain terms?1 / 10
Head is the pump's pressure output re-expressed as an equivalent height of fluid column. A pump rated at 10 m of head could, in principle, push water straight up a vertical pipe 10 m before running out of push — that's much easier to picture than a raw pressure number in pascals.
Engineering · L3 · Pumps & Head
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Engineering · L3 · Pumps & HeadFlashcards9 cards
What does a material's R-value measure?1 / 9
R-value is a number that quantifies how well a material resists the flow of heat through it — the higher the R-value, the better the material insulates. It's a property of a specific thickness of material, not just the material itself.
Engineering · L3 · R-Value & Thermal Resistance
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Engineering · L3 · R-Value & Thermal ResistanceFlashcards8 cards
A 20 m² wall has R-13 insulation. Indoor temperature is 21 °C and outdoor is -4 °C (ΔT = 25 °C). What is the rate of heat loss through the wall? (Use R-13 ≈ 2.3 m²·°C/W)1 / 8
Q/t = A·ΔT/R = 20 × 25 / 2.3 = 500 / 2.3 ≈ 217 W.
Engineering · L3 · R-Value & Thermal Resistance
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Engineering · L3 · R-Value & Thermal ResistanceFlashcards9 cards
What is a task, in project scheduling?1 / 9
A single piece of work with a clear start and end — small enough to estimate a duration for, and to say plainly when it is done. A project is broken down into a list of tasks before it is scheduled.
Engineering · L3 · Project Scheduling
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Engineering · L3 · Project SchedulingFlashcards8 cards
A treehouse project has these tasks: buy materials (2 days), cut wood (1 day, needs materials), assemble frame (3 days, needs cut wood), add roof (1 day, needs frame), buy paint (1 day, no dependency), paint treehouse (1 day, needs roof AND paint). What is the critical path?1 / 8
Trace the chain of tasks that must happen strictly one after another with no slack.
Engineering · L3 · Project Scheduling
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Engineering · L3 · Project SchedulingFlashcards10 cards
What is Design for Manufacturing (DFM)?1 / 10
Designing a part so it is easy, fast, and cheap to actually manufacture — not just easy to draw on paper. DFM asks "how will this really get made?" at the design stage, before any tooling is cut.
Engineering · L3 · Design for Manufacturing
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Engineering · L3 · Design for ManufacturingFlashcards9 cards
In the bracket case study, what was wrong with the original design's part count?1 / 9
It was made of 5 separate pieces — a bracket, two spacers, and two fasteners — that all had to be sourced and assembled by hand, when the same job could be done by far fewer parts.
Engineering · L3 · Design for Manufacturing
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Engineering · L3 · Design for ManufacturingFlashcards12 cards
What are the two conditions for static equilibrium of a rigid body?1 / 12
ΣF = 0 (net force is zero in all directions) AND Στ = 0 (net torque is zero about any point). Both must be satisfied simultaneously. In 2D this gives three scalar equations: ΣFx = 0, ΣFy = 0, ΣM_A = 0.
Engineering · L4 · Statics — Equilibrium & Free-Body Analysis
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Engineering · L4 · Statics — Equilibrium & Free-Body AnalysisFlashcards13 cards
Define engineering stress σ and engineering strain ε.1 / 13
σ = F/A₀ (force over original cross-sectional area, Pa or MPa). ε = ΔL/L₀ (change in length over original length, dimensionless). These are 'engineering' values; true stress/strain use instantaneous area/length. For small deformations they are approximately equal.
Engineering · L4 · Mechanics of Materials — Stress, Strain & Failure
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Engineering · L4 · Mechanics of Materials — Stress, Strain & FailureFlashcards12 cards
State KVL and KCL and their physical basis.1 / 12
KVL (Kirchhoff's Voltage Law): the sum of voltages around any closed loop is zero — based on conservation of energy. KCL (Kirchhoff's Current Law): the sum of currents entering a node equals the sum leaving — based on conservation of charge. Together they are the foundation of all circuit analysis.
Engineering · L4 · Electric Circuits — DC & AC Analysis
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Engineering · L4 · Electric Circuits — DC & AC AnalysisFlashcards10 cards
What is a feedback control system and why is feedback used?1 / 10
A feedback (closed-loop) control system measures the output, compares it to a desired setpoint, and uses the error to drive an actuator. Feedback compensates for disturbances, plant uncertainty, and model error — making the system robust. Without feedback (open-loop), a single disturbance drives the output away from setpoint indefinitely.
Engineering · L4 · Control Systems — Fundamentals & PID
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Engineering · L4 · Control Systems — Fundamentals & PIDFlashcards11 cards
What is the steady-flow energy equation (SFEE) for an open system?1 / 11
Q̇ − Ẇ_s = ṁ[(h₂ − h₁) + (V₂² − V₁²)/2 + g(z₂ − z₁)], where h is specific enthalpy, V is fluid velocity, z is elevation, and ṁ is mass flow rate. This is the first law applied to an open system in steady state — the basis of turbine, compressor, nozzle, and heat-exchanger analysis.
Engineering · L4 · Engineering Thermodynamics & Fluid Mechanics
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Engineering · L4 · Engineering Thermodynamics & Fluid MechanicsFlashcards8 cards
Write the lift and drag equations, and name every term.1 / 8
L = ½ρV²S·C_L and D = ½ρV²S·C_D. ρ = air density, V = airspeed, S = reference (wing planform) area, C_L and C_D are the dimensionless lift and drag coefficients that capture the effect of shape and angle of attack. Both forces scale with the square of airspeed.
Engineering · L4 · Aerodynamics
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Engineering · L4 · AerodynamicsFlashcards8 cards
What is the fundamental difference between subtractive, additive, and forming manufacturing processes?1 / 8
Subtractive: material is removed from a solid block (milling, turning, drilling) to reach the final shape. Additive: material is built up layer by layer (3D printing) from a digital model. Forming: a fixed volume of material is plastically deformed into shape (forging, rolling, stamping) with no material added or removed.
Engineering · L4 · Manufacturing Processes & GD&T
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Engineering · L4 · Manufacturing Processes & GD&TFlashcards8 cards
What is an ideal transformer, and how do the turns ratio, voltage, and current relate?1 / 8
An ideal transformer couples two windings through a shared magnetic core with no losses. Turns ratio a = N₁/N₂. Voltage transforms directly: V₂/V₁ = N₂/N₁ = 1/a. Current transforms inversely (to conserve power): I₂/I₁ = N₁/N₂ = a. Ideal power in equals power out: V₁I₁ = V₂I₂.
Engineering · L4 · Electrical Machines & Power Systems
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Engineering · L4 · Electrical Machines & Power SystemsFlashcards8 cards
What makes a system linear and time-invariant (LTI), and why does that matter?1 / 8
Linear: the response to a weighted sum of inputs equals the same weighted sum of responses (superposition). Time-invariant: a shifted input produces an identically shifted output. LTI systems matter because they are fully characterised by a single function — the impulse response h(t) — from which the response to any input can be computed by convolution.
Engineering · L4 · Signals & Systems
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Engineering · L4 · Signals & SystemsFlashcards8 cards
What is the natural frequency ωₙ of an undamped spring-mass system, and how is it derived?1 / 8
ωₙ = √(k/m) rad/s. Free vibration of an undamped mass on a spring obeys mẍ + kx = 0. Substituting x = e^(st) gives the characteristic equation ms² + k = 0, with roots s = ±j√(k/m) — purely imaginary, so the mass oscillates sinusoidally forever at ωₙ with no energy loss.
Engineering · L4 · Mechanical Vibrations
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Engineering · L4 · Mechanical VibrationsFlashcards5 cards
What is the weak (variational) form of a BVP, and why is it preferred over the strong form in FEM?1 / 5
The weak form is obtained by multiplying the PDE by a test function v in a suitable Sobolev space and integrating by parts to transfer derivatives off the solution onto v. It requires only square-integrable first derivatives (H¹ regularity) rather than pointwise second derivatives, allowing piecewise-polynomial (finite element) approximations that would violate the strong form. Natural (Neumann) boundary conditions are incorporated automatically during integration by parts.
Engineering · L5 · Finite Element Method
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Engineering · L5 · Finite Element MethodFlashcards4 cards
State the LQR problem: what system does it control and what cost does it minimise?1 / 4
For the linear time-invariant system ẋ = Ax + Bu, the LQR minimises the infinite-horizon quadratic cost J = ∫₀^∞ (xᵀQx + uᵀRu) dt, where Q ⪰ 0 (positive semi-definite, state penalty) and R ≻ 0 (positive definite, control effort penalty). The matrices Q and R encode the designer's trade-off between state deviation and actuator effort.
Engineering · L5 · Optimal Control & LQR
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Engineering · L5 · Optimal Control & LQRFlashcards8 cards
What problem does the Kalman filter solve, and what are its two governing equations?1 / 8
It recursively estimates the state of a linear system from noisy measurements. Process model: xₖ = Axₖ₋₁ + Buₖ₋₁ + wₖ₋₁ (process noise w ~ N(0,Q)). Measurement model: zₖ = Hxₖ + vₖ (measurement noise v ~ N(0,R)). The filter fuses the model's prediction with each new noisy measurement, weighted by their relative uncertainty.
Engineering · L5 · Kalman Filtering & State Estimation
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Engineering · L5 · Kalman Filtering & State EstimationFlashcards8 cards
What is the core idea of model predictive control (MPC)?1 / 8
At every time step, MPC uses a model of the plant to predict its behaviour over a finite future horizon, solves an optimization problem for the control sequence that minimises a cost over that horizon subject to constraints, applies only the FIRST control action, then re-solves the whole problem again at the next step with a newly measured state — this repeated re-optimization is called the receding horizon principle.
Engineering · L5 · Model Predictive Control
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Engineering · L5 · Model Predictive ControlFlashcards9 cards
What is forward kinematics for a robotic manipulator?1 / 9
Forward kinematics computes the end-effector's position and orientation (pose) given the joint angles/displacements q = [q₁,...,qₙ]. It is found by composing a homogeneous transformation matrix for each joint-link pair, T = T₁(q₁)T₂(q₂)···Tₙ(qₙ), and reading the end-effector pose from the resulting 4×4 matrix. Forward kinematics always has a unique solution.
Engineering · L5 · Robot Kinematics & Dynamics
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Engineering · L5 · Robot Kinematics & DynamicsQuiz3 questions
A seesaw is an example of which simple machine?
ARampBWheelCLeverDPulley
Engineering · L1 · Simple Machines Quiz
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Engineering · L1 · Simple Machines QuizQuiz2 questions
What is the first step of the engineering design process?
ABuildBTestCAskDImagine
Engineering · L1 · Design Process Quiz
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Engineering · L1 · Design Process QuizQuiz4 questions
What does it mean if a material is 'flexible'?
AIt can bend without breakingBIt is see-throughCIt never gets wetDIt is very heavy
Engineering · L1 · What Are Materials? Quiz
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Engineering · L1 · What Are Materials? QuizQuiz4 questions
What happens when you push sideways on a square frame?
AIt stays exactly the sameBIt leans over into a slanted shapeCIt breaks into piecesDIt turns into a circle
Engineering · L1 · Strong Shapes Quiz
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Engineering · L1 · Strong Shapes QuizQuiz4 questions
Which four parts do you need to build a simple bulb circuit?
ABattery, wire, bulb, switchBBattery, glue, paper, tapeCWire, magnet, wood, nailDBulb, water, wire, plastic
Engineering · L1 · Building Simple Circuits Quiz
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Engineering · L1 · Building Simple Circuits QuizQuiz4 questions
Which tool would you use to measure how long your desk is?
AScissorsBRulerCGlueDHammer
Engineering · L1 · Tools & Safety Quiz
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Engineering · L1 · Tools & Safety QuizQuiz4 questions
Why must pipe joints be sealed tight, with no gaps?
ASo the pipe looks nicerBSo water does not leak outCSo the pipe weighs lessDSo the water turns a different colour
Engineering · L1 · Pipes & Water Flow Quiz
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Engineering · L1 · Pipes & Water Flow Quiz