📖 Notes
LESSON 12 OF 17
Forces & Motion, MDCAT-Style
Forces & Motion, MDCAT-Style
Kinematics equations, Newton's three laws, momentum conservation, and work-energy-power — the mechanics foundation for every physics question that follows.
Kinematics
The Four Kinematics Equations
Kinematics Equations
REFERENCEv = u + at s = ut + ½at² v² = u² + 2as s = (u+v)t/2
Newton's Three Laws
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1st Law — Inertia
An object keeps its state of motion unless a net force acts. Published by Newton in 1687 in the Principia.
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2nd Law — F = ma
Force equals mass times acceleration — the single most-used equation in MDCAT mechanics.
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3rd Law — Action/Reaction
Every force has an equal, opposite reaction force — why a rocket engine pushes exhaust down to push the rocket up.
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SI unit of force
The newton (N) = 1 kg·m/s², named after Isaac Newton himself.
- 1st Law (Inertia): no net force means no change in motion
- 2nd Law: F = ma
- 3rd Law: every action has an equal and opposite reaction
Momentum
- p = mv
- Impulse = Ft = Δp
- Momentum is conserved — total momentum stays constant in a closed system
Work, Energy & Power
- W = Fs cosθ
- KE = ½mv²
- PE = mgh
- Power = W/t = Fv
- Efficiency = useful output / total input × 100%