By domain
Physics
Everything in Nalanda that sits under physics.
35 entries
Acceleration
Acceleration is the rate of change of velocity, and because velocity has both a size and a direction, an object accelerates whenever it speeds up, slows down, or merely changes direction, even at constant speed.
7 min
ConceptAction-reaction pairs
Every force one object exerts on a second is matched, at the same instant, by an equal and opposite force the second exerts back on the first, and this pairing is what makes pushing off anything, including empty exhaust gas, actually work.
7 min
ConceptAngular momentum
Angular momentum is rotational inertia times angular velocity, and it stays constant whenever no outside torque acts, which is why spin speeds up as mass pulls inward.
7 min
ConceptCenter of mass and balance
The center of mass is the single point where a distributed body's mass can be treated as concentrated for the purpose of predicting how the whole body moves and whether it stays balanced.
7 min
ConceptCircular motion and inward acceleration
Moving at constant speed along a circle still requires acceleration, because velocity's direction is constantly changing, and that acceleration always points toward the center.
7 min
ConceptConservation of mechanical energy
When only conservative forces act, the sum of kinetic and potential energy stays fixed, letting you compare two moments of motion without tracing the path between them.
6 min
Mental modelDimensional analysis in physics
Every physical quantity carries dimensions built from a small set of base quantities, and any equation claiming to describe nature must have the same dimensions on both sides, which lets you test or repair a formula before ever taking data.
6 min
ConceptElastic and inelastic collisions
Momentum is conserved in every collision between isolated bodies, but kinetic energy is conserved only in the special case of a perfectly elastic collision.
7 min
ConceptForce as interaction
A force is not a substance an object carries; it is what one object does to another during an interaction, and every force names a specific pair and a specific cause.
7 min
ConceptImpulse and force over time
The same change in momentum can come from a large force acting briefly or a small force acting longer, since impulse, force multiplied by the time it acts, is what equals the change in momentum.
6 min
ConceptInertia and the persistence of motion
Inertia is the tendency of an object to keep whatever velocity it already has, constant speed in a constant direction, unless something acts on it to change that velocity, which means force is needed to change motion, not to maintain it.
7 min
ConceptKinetic energy
Kinetic energy is the energy a moving object carries by virtue of its motion, equal to one half its mass times the square of its speed, derived directly from the work needed to accelerate it from rest.
7 min
ConceptKinetic friction and energy loss
Kinetic friction is a roughly constant force opposing sliding motion that converts organized kinetic energy into heat at the contact interface, at a rate set by the normal force and a material coefficient.
6 min
ConceptMass as resistance to acceleration
Mass is not how much stuff an object has or how big it looks; it is a measured resistance, how much acceleration a given force fails to produce.
7 min
ConceptMomentum as quantity of motion
Momentum, mass times velocity, is conserved for an isolated system because every internal force comes paired with an equal and opposite reaction acting for the same time.
6 min
ConceptMotion graphs
Position time, velocity time, and acceleration time graphs are three pictures of the same motion, connected because slope on one graph gives the value plotted on the next, and area under one gives the change plotted on the graph before it.
7 min
ConceptNormal force and contact constraints
The normal force is the perpendicular push a rigid surface supplies, adjusted to whatever value stops an object from passing through it, not a fixed force equal to weight.
7 min
ConceptObservation, measurement, and physical quantities
A physical quantity is not a private sensation but whatever a stated, repeatable procedure of comparison assigns a number and a unit to.
5 min
ConceptPhysical models and idealization
A physical model is a deliberately simplified stand in for a real system, built by naming and discarding certain features on purpose, and it is only useful once you can state what it ignores and where that neglect starts to matter.
6 min
ConceptPosition, distance, and displacement
Position is where something is relative to a chosen origin, distance is the total length of the path travelled, and displacement is the straight, directed change between start and end, and the three are related but never interchangeable.
7 min
ConceptPotential energy and configuration
Potential energy is the work a configuration of interacting objects could still do, stored not in one object but in the relationship between them and a reference.
6 min
ConceptPrecision, accuracy, and uncertainty
Precision is how repeatable a measurement is, accuracy is how close it is to the true value, and uncertainty is the honestly stated range within which the true value probably lies.
6 min
ConceptReference frames and relative description
Motion has no meaning stated in isolation; every description of position, velocity, or rest is a description relative to a chosen frame of reference, and changing the frame changes the description without changing what physically happens.
6 min
ConceptRotational inertia
Rotational inertia measures how hard it is to change a body's spin, and it depends not just on how much mass there is, but on how far that mass sits from the axis of rotation.
7 min
ConceptSpeed and velocity
Speed is how fast the distance odometer is ticking, a plain number with no direction, while velocity is the rate of change of displacement, a directed quantity that can be zero, positive, or negative even while speed stays constant.
6 min
ConceptStatic equilibrium
A rigid body genuinely at rest must satisfy two independent conditions at once: zero net force, so it does not start moving, and zero net torque, so it does not start turning.
7 min
ConceptStatic friction
Static friction is not a fixed force but a responsive one, matching whatever is needed to keep two touching surfaces from sliding, up to a maximum set by the normal force and a material coefficient.
6 min
ConceptTension in strings and cables
Tension is the pulling force transmitted along a flexible connector such as a string or cable, uniform along an ideal massless, frictionless length and solved for by applying Newton's second law to each body it connects.
7 min
ConceptThe relation between force, mass, and acceleration
Net force, mass, and acceleration are locked together by one relation, net force equals mass times acceleration, and it can be reconstructed, not just memorized, from how force and mass were separately defined.
7 min
ConceptTorque and rotational effect
Torque is the turning effect of a force, set by how much force you apply, how far from the pivot, and at what angle.
7 min
ConceptTwo-dimensional motion and projectiles
Motion in two dimensions, including a thrown or launched projectile's curved path, can be built exactly by treating the horizontal and vertical motions as two independent one-dimensional motions happening at the same time, sharing only the clock.
7 min
ConceptUnits, standards, and calibration
A unit is an agreed, reproducible reference amount, and calibration is the act of comparing an instrument against that reference so its readings can be trusted by anyone, not just its owner.
6 min
ConceptUniversal gravitation
Every two masses in the universe pull on each other with a force that grows with both masses and falls off as the square of the distance between them, the same law that governs a falling apple and a moon in orbit.
8 min
ConceptWeight and gravitational interaction
Weight is not a property an object owns; it is the specific gravitational force pulling on it right now, which is why the same object weighs differently on the Moon, in an accelerating elevator, and in orbit, while its mass never changes at all.
7 min
ConceptWork as force through distance
Work is the transfer of mechanical energy by a force, measured as the component of that force along an object's displacement times the distance moved, and it is zero whenever force and motion are perpendicular.
7 min