Dynamics: Forces and Motion

1. Introduction to Dynamics

Dynamics is the study of the connection between force and motion. Forces cause objects to:

  • Start or stop moving
  • Speed up or slow down
  • Change direction

2. Force

Definition: A vector quantity that changes or tends to change the state of a body.

Types of Forces:

A. Contact Forces

  • Normal force
  • Thrust
  • Friction
  • Tension
  • Elastic forces

B. Non-Contact Forces

  • Gravitational force
  • Electrostatic force
  • Magnetic force

3. Fundamental Forces in Nature

Strong Nuclear Force

it binds the fundamental particles of matter together to form larger particles. It holds together the quarks that make up protons and neutrons, and part of the strong force also keeps the protons and neutrons of an atom'snucleus together. The strongest force, but also has a short range. It governs nuclear interactions inside atoms. Strongest force, keeps protons packed in atomic nucleus.

  • Exchange Particles: Pions and other heavy particles
  • Range: 10^-15 m (≈ diameter of a proton)
  • Relative Strength: 1

Comparison Table

ForceRangeRelative StrengthExchange Particles
Strong Nuclear Force10^-15 m (≈ diameter of a proton)1Pions and other heavy particles
Electromagnetic ForceInfinite7.3 x 10^-3Photons
Gravitational ForceInfinite6 x 10^-39Graviton (not yet detected)
Weak Nuclear Force10^-18 m10^-13W+, W-, Z0 (vector bosons)

Unification Attempts

The most successful unification attempt is the electroweak theory, proposed by Abdus Salam, Steven Weinberg, and Sheldon Lee Glashow. It combines electromagnetic and weak forces, incorporating quantum electrodynamics with four carrier particles: photon, W+, W-, and Z particles.

4. Force Diagrams

  • System Diagrams (SD): Visual representation of all objects involved
  • Free-Body Diagrams (FBD): Schematic of single object with force vectors

5. Net Force

  • Sum of all forces acting on an object
  • Determines if forces are balanced or unbalanced
  • Balanced forces: Net force = 0 N (no change in motion)
  • Unbalanced forces: Net force ≠ 0 N (change in motion)

6. Vector Addition of Forces

  • Like parallel forces: Add magnitudes
  • Unlike parallel forces: Subtract magnitudes
  • Non-parallel forces: Use head-to-tail rule or coordinate system