# Academa > Academa, Inc. is a Delaware C corporation founded by Sina Atalay, co-founder and CEO, and Abdullah Geduk, co-founder and CTO. Sina is a Princeton PhD student currently on leave; Abdullah is a Penn State PhD student. Close friends who have built together since undergrad, they created Academa to make technical knowledge easier to understand through visual lectures and let learners request new lecture videos. Published by [Academa, Inc.](https://academa.ai). Primary language: en-US. Each video link below is a complete Markdown alternate containing the lecture summary, metadata, chapters, timestamp links, full transcript, and a timestamped account of everything shown in the film. ## Video lectures - [Alternating Current: Phasors and Power Factor](https://academa.ai/lectures/alternating-current-phasors-power-factor.md): Engineering; 19 minutes 9 seconds. Phasors, impedance and power factor for AC circuits: why current lags, what reactive power costs, and how a capacitor fixes it. - [Backpropagation by Hand: From Computational Graphs to Matrix Gradients](https://academa.ai/lectures/backpropagation-is-the-chain-rule-on-a-graph.md): Machine Learning; 19 minutes 29 seconds. Follow a tiny neural network through exact forward values, scalar chain-rule backpropagation, matrix gradients, and activation-memory costs. - [The Bloom Filter](https://academa.ai/lectures/bloom-filters.md): Computer Science; 14 minutes 17 seconds. How a Bloom filter tests membership in a few bits per item, why false positives happen, how to pick k, and why deletion is forbidden. - [Comparative Advantage: Why Both Countries Gain from Trade](https://academa.ai/lectures/comparative-advantage-gains-from-trade.md): Economics; 16 minutes 3 seconds. Why two countries both gain from trade even when one is slower at everything: opportunity cost, specialization and the frontier. - [Cournot Competition: Best-Response Dynamics and the Race to Equilibrium](https://academa.ai/lectures/cournot-duopoly-and-best-responses.md): Economics; 17 minutes 16 seconds. Watch Cournot firms chase best responses to equilibrium, then compare its price with monopoly, competition, and Bertrand pricing. - [Shear and Moment Diagrams from First Principles](https://academa.ai/lectures/deriving-shear-moment-diagrams.md): Engineering; 17 minutes 55 seconds. Cut a beam, take the free body, and derive shear and moment diagrams from equilibrium, then from the two derivatives that govern them. - [Why Wind Tunnel Models Work: Dimensional Analysis of Aerodynamic Drag](https://academa.ai/lectures/dimensional-analysis-drag.md): Engineering; 17 minutes. Why a scale model predicts the drag on a real aircraft: count the dimensions, derive Reynolds and the drag coefficient, and see where Mach breaks similarity. - [Edit Distance: From Memorization to Derivation](https://academa.ai/lectures/edit-distance-dp-derivation.md): Computer Science; 15 minutes 43 seconds. Derive the edit distance recurrence, fill its table cell by cell, recover the edits, and count the work plain recursion repeats. - [Euler Buckling: Why Slender Columns Fail by Instability](https://academa.ai/lectures/euler-buckling-columns.md): Engineering; 17 minutes 32 seconds. Why slender columns buckle: the critical load derived from the deflected shape, effective length from inflection points, and the slenderness limit. - [Frequency Response: From Poles and Zeros to Stability and Compensation](https://academa.ai/lectures/frequency-response-bode-closed-loop.md): Engineering; 27 minutes 40 seconds. Build Bode magnitude and phase curves from poles and zeros, define gain and phase margin, then see what lag and lead compensators change. - [The Halting Problem Is Undecidable](https://academa.ai/lectures/halting-problem-undecidability.md): Computer Science; 16 minutes 32 seconds. Cantor's diagonal, the table of programs against inputs, and the contrary program that proves no halting decider can exist. - [Kinematics of a Body: The Instantaneous Axis](https://academa.ai/lectures/instantaneous-axis-of-rotation.md): Engineering; 8 minutes 1 second. The rigid-body velocity relation, the instantaneous centre of a rolling wheel, and the screw axis that replaces it in three dimensions. - [Maximum Flow Equals Minimum Cut: Proof by Example](https://academa.ai/lectures/maxflow-mincut-theorem.md): Computer Science; 18 minutes 59 seconds. Max flow equals min cut, worked by hand on one small network: augmenting paths, a residual backward edge, and the cut that certifies the answer. - [Monopoly, Marginal Revenue, and Price Discrimination](https://academa.ai/lectures/monopoly-marginal-revenue-and-price-discrimination.md): Economics; 15 minutes 36 seconds. Derive monopoly marginal revenue, compare monopoly with competition, and trace welfare under group and perfect price discrimination. - [How Hyperlinks Become Votes: The PageRank Algorithm](https://academa.ai/lectures/pagerank-the-random-surfer.md): Computer Science; 11 minutes 21 seconds. Build PageRank from a random surfer on six pages: link matrix, power iteration, damping factor, dangling pages and rank sinks. - [PID Control, One Term at a Time](https://academa.ai/lectures/pid-control-one-term-at-a-time.md): Engineering; 16 minutes 42 seconds. Build a PID controller one term at a time on a cruise control: proportional offset, integral windup, derivative damping, and tuning. - [Planar Truss Analysis: Method of Joints](https://academa.ai/lectures/planar-truss-method-of-joints.md): Engineering; 15 minutes 36 seconds. Analyse one planar truss by the method of joints: support reactions, joint equilibrium, tension and compression signs, zero force members. - [Automata Behind Regular Expressions](https://academa.ai/lectures/regex-to-automata.md): Computer Science; 17 minutes 40 seconds. Build the state machine behind a regular expression, run a string through it, determinise it, and meet the two things regexes cannot do. - [Why Truthful Bidding Works—and Why First-Price Bidders Shade](https://academa.ai/lectures/second-price-auctions-and-honest-bidding.md): Economics; 12 minutes 49 seconds. See truthful bidding proved by cases, first-price bid shading derived from incentives, and revenue equivalence stated with its assumptions. - [Solving 2×2 Games by Hand: Best Responses, Pure Equilibria, and Mixing](https://academa.ai/lectures/solving-2-2-games-best-responses-pure-and-mixed-nash-equilibria.md): Economics; 23 minutes 22 seconds. Solve 2×2 games by hand using payoff matrices, best-response marks, pure Nash equilibria, expected payoffs, and mixed strategies. - [Supply and Demand in Motion: Equilibrium, Shifts, and Movements Along Curves](https://academa.ai/lectures/supply-and-demand-actually-moving.md): Economics; 14 minutes 15 seconds. Learn supply, demand, and equilibrium, then see how harvests, tastes, and new competitors shift curves and change market outcomes. - [The Market for Lemons: How Hidden Quality Can Make Good Products Disappear](https://academa.ai/lectures/the-market-for-lemons-how-hidden-quality-can-cause-a-market-collapse.md): Economics; 12 minutes 33 seconds. A used-car example explains adverse selection, market unraveling, the value of visible quality, and what common repairs actually fix. - [NP-Completeness and Reduction: From Definitions to the 3-SAT to Vertex Cover Proof](https://academa.ai/lectures/three-sat-vertex-cover-reduction.md): Computer Science; 21 minutes 2 seconds. P and NP defined by verifiers, then the 3-SAT to Vertex Cover reduction built and argued in both directions on one formula. - [Torsion: From Geometry to Shaft Design](https://academa.ai/lectures/torsion-shafts.md): Engineering; 12 minutes 57 seconds. How twisting a round shaft gives shear strain linear in radius, the torque integral, the polar moment of area, and why drive shafts are tubes. - [Who Really Bears a Tax? Tax Incidence, Elasticity, and Deadweight Loss](https://academa.ai/lectures/who-really-pays-a-tax.md): Economics; 13 minutes 34 seconds. See how elasticities split a per-unit tax, why remittance rules do not decide incidence, and why deadweight loss rises with tax squared. ## Pages - [Technical Knowledge, Explained Visually \| Academa](https://academa.ai/): Explore hand-maintained technical lecture videos, chat alongside each video, or ask Academa to create a new lecture about any technical topic. - [Video lectures in mathematics \| Academa](https://academa.ai/lectures): Explore Academa’s complete collection of technical lecture videos, organized by subject, with chapters, transcripts, and AI chat that understands each video. - [Pricing \| Academa](https://academa.ai/pricing): Compare Academa’s Free, Plus, and Enterprise plans for watching technical lecture videos, chatting with videos, and generating lectures on demand. - [Privacy \| Academa](https://academa.ai/privacy): How Academa collects, uses, discloses, retains, and protects information across lectures, tutor conversations, accounts, analytics, and billing. - [Computer Science lectures \| Academa](https://academa.ai/subjects/computer-science): Explore 7 computer science lectures on Academa, with AI chat that understands each lecture. - [Economics lectures \| Academa](https://academa.ai/subjects/economics): Explore 8 economics lectures on Academa, with AI chat that understands each lecture. - [Engineering lectures \| Academa](https://academa.ai/subjects/engineering): Explore 9 engineering lectures on Academa, with AI chat that understands each lecture. - [Machine Learning lectures \| Academa](https://academa.ai/subjects/machine-learning): Explore 1 machine learning lecture on Academa, with AI chat that understands each lecture. - [Team \| Academa](https://academa.ai/team): Meet Academa co-founders Sina Atalay and Abdullah Geduk, close friends who have been building together since undergrad. - [Terms \| Academa](https://academa.ai/terms): The agreement governing Academa accounts, AI-generated lectures and tutor answers, public content, paid plans, ownership, and disputes.