02Physics, Part I (Class XI; reprint 2026–27)National Council of Educational Research and Training (NCERT)Textbook chapter · PDFChapter Four: Laws of Motionncert.nic.in
OpenStax 5.3, equation 5.3 and inertial-frame discussion; NASA comparison of force, mass, acceleration and SI newton.
2026-10-10 · Constant-mass Newtonian relation and units only; this does not extend F = ma unchanged to relativistic or variable-mass systems.
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2026-10-10 · Fresh primary-source inspection of the complete compact record, including every statement, equation, quantity and material condition, followed by independent AI editorial review. This check does not certify all linked lessons or every passage of every cited publication.
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Agreement within this scope
In classical constant-mass mechanics, resultant force is mass times acceleration.
The resultant includes all external forces; the inertial-frame and constant-mass qualifications remain essential.
For fixed-mass Newtonian particles with cancelling internal force pairs, the centre of mass R is the mass-weighted position and M R̈ equals total external force.
Newtonian fixed-particle force sum with cancelling internal pairs.
The linear oscillator model m ẍ + b ẋ + kx = F₀ sin(Ωt) has a steady sinusoidal response when transients decay. Its amplitude depends on drive frequency and damping.
Constant-mass Newtonian balance with specified linear spring, damping and drive forces.
For a frame rotating at constant Ω about a common inertial origin, a_inertial=a_rot+2Ω×v_rot+Ω×(Ω×r). Newton's law in that rotating frame therefore includes the inertial forces −2mΩ×v_rot and −mΩ×(Ω×r).
Newton's inertial force balance changes coordinate acceleration by the stated constant-rotation terms.
For a smooth classical fluid with mass continuity, material acceleration is D_tv=∂_tv+(v·∇)v and inviscid momentum obeys ρD_tv=−∇P+ρg. In conservation form, ∂_t(ρv)+∇·(ρv⊗v+P𝟙)=ρg; pressure, density and thermodynamic closure must be supplied with initial/boundary data.
Pressure/body-force balance applies Newtonian acceleration to an ideal continuum parcel.
Gravity supplies both downslope shear and normal loading on a slope. Stability depends on resisting strength as well as geometry; fractures, bedding and weathering can create weaknesses. Water changes intergranular forces and pore-pressure conditions, so a change in moisture or loading can change the likelihood of movement.
Gravity and contact forces enter the mechanical balance.
When vertical acceleration is negligible, the vertical pressure gradient balances gravity: ∂p/∂z=−ρg for upward z. This relates pressure to the overlying mass distribution. An equation of state and boundary conditions are additionally needed to obtain a pressure profile.
Hydrostatic balance is a bounded acceleration-negligible force balance.
An inertial frame is one in which a free Newtonian particle moves at constant velocity. A nonrotating frame moving at constant velocity relative to an inertial frame is also inertial. Mass measures resistance to acceleration in Newton’s second law; inertia is not an additional force that must sustain motion.
This relation concerns the stated inertial reference frames and inertia claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
For a particle on a circle of fixed radius R, acceleration has inward radial component v²/R and tangential component dv/dt. Uniform circular motion has v=Rω and inward acceleration Rω². “Centripetal force” names the inward net-force component required by the motion; tension, gravity or another interaction supplies it.
This relation concerns the stated circular motion and centripetal acceleration claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
In a Newtonian gravitational field g, gravitational weight is W=mg. Mass and weight are different quantities: changing the local field changes weight without changing the body’s mass. A supporting scale measures a contact force, often called apparent weight; in free fall that support can vanish while gravity remains present.
This relation concerns the stated mass, gravitational weight and apparent weight claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
A normal force is the perpendicular component of a contact force. Tension in an ideal flexible connector pulls along the connector; a slack ideal rope cannot transmit compression. The contact/tension magnitudes are solved from dynamics and constraints, rather than being universally equal to weight. A massless taut connector over a frictionless ideal pulley has the same tension magnitude along it.
This relation concerns the stated normal forces and tension claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
A free-body diagram represents all external forces acting on the selected body or system. Forces the system exerts on its surroundings belong on another system’s diagram. A force and its components are alternative representations, and the net force is their sum rather than an extra force. For an extended body, force locations are also needed to determine torque.
This relation concerns the stated free-body diagrams and system boundaries claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
In the simple dry-contact model, static friction adjusts to prevent tangential relative slip up to |F_s|≤μ_sN. During sliding, kinetic friction has magnitude approximately μ_kN and opposes relative sliding at the contact. Static friction need not be at its limit and can accelerate a body or act in its direction of motion.
This relation concerns the stated static and kinetic dry friction claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
For a specified body and regime, an approximate quadratic drag magnitude is F_D=ρC_DAv_rel²/2, opposing relative motion through the fluid. A vertical falling body reaches a terminal speed when gravity, drag and any buoyancy balance. Neglecting buoyancy in a constant-coefficient model gives v_T=√(2mg/(ρC_DA)).
This relation concerns the stated fluid drag and terminal speed claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
For a constant-mass Newtonian particle in an inertial frame, linear momentum is p=mv and net-force impulse over an interval is J=∫F_netdt=p_f−p_i. For a fixed many-particle system, the external impulse changes total momentum when internal force pairs cancel. A large collision force over a short time is governed by the impulse, not force magnitude alone.
This relation concerns the stated impulse and momentum transfer claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
An ideal one-dimensional spring has restoring force F=−kx and potential energy U=kx²/2 relative to equilibrium. The force law is an approximate material/geometry model valid over its linear elastic range, not a universal response of every deformable object.
This relation concerns the stated hooke’s spring model and elastic energy claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
Average mass density is m/V. Fluid pressure parameterizes isotropic normal stress, with positive p denoting compression: uniform signed pressure p on a plane area A produces normal force magnitude |p|A. With nonuniform pressure, force must be integrated over the surface. Pressure and density describe different quantities and neither is a total force.
This relation concerns the stated density and fluid pressure claim and its conditions; it does not assert an unqualified prerequisite or an additional theorem.
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