Physics in Everyday Life – Introduction to Motion

Physics in Everyday Life: Introduction to Motion

Context, Purpose, & Relevance

  • Course/Module: General Science – Physics in Everyday Life (Senior High School)
  • Session Focus: Introduction to Motion
  • Rationale
    • Understanding science starts with physics because physics lays the conceptual foundation for other sciences (chemistry, biology, earth science, etc.).
    • Everyday experiences (walking, riding a train, pushing a cart) are governed by physical principles; recognizing these fosters scientific literacy and critical thinking.
    • Ethical & practical angle: accurate physics knowledge underpins safe engineering, responsible technology use, and informed societal decisions (e.g.
      traffic safety, energy consumption).

Warm-Up / Engagement Task

  • Students asked to list 5 everyday activities/events to highlight the ubiquity of motion and physical interactions (examples could include: commuting, sports, cooking, using a phone, opening a door).

What Is Physics?

  • "The Basic Science" because all natural phenomena ultimately reduce to physical interactions.
  • Scope includes:
    • Motion & forces
    • Energy & matter
    • Heat, sound, & light
    • Structure of atoms
  • Real-world relevance: from household appliances to astrophysical observations.

Branches of Physics

  • ### Classical Physics (pre-20th-century discoveries; macroscopic, low-speed regime)
    • Motion (mechanics)
    • Fluids (hydrodynamics & aerodynamics)
    • Heat (thermodynamics)
    • Sound (acoustics)
    • Light (geometrical & physical optics)
    • Electricity (electrostatics & circuits)
    • Magnetism (magnetostatics & electromagnetism)
  • ### Modern Physics (20th C → present; microscopic, high-speed, high-energy)
    • Relativity (special & general)
    • Atomic structure
    • Quantum theory
    • Condensed matter physics
    • Nuclear physics
    • Astrophysics & cosmology
  • Pedagogical link: Motion (classical mechanics) is foundational for both classical and modern sub-domains.

Fundamental Concepts of Motion

  • Motion: change in position of an object relative to surroundings/reference point over time.
  • Necessity of a reference frame: motion is relative, not absolute.

Types of Motion

  1. Translational Motion
    • Straight-line or curved-path movement without rotation.
    • Examples: car driving along a road, projectile arc.
  2. Rotational Motion
    • Object spins about an axis.
    • Examples: spinning top, Earth’s rotation, wheels turning.

Reference-Frame Illustration

  • Scenario: You sit in a moving train while a friend walks down the aisle.
    1. Relative to you: friend moves at walking speed (~1\text{–}2\,\mathrm{m/s}) in aisle direction.
    2. Relative to train: friend’s motion is confined to aisle; train interior treats aisle floor as rest frame.
    3. Relative to ground: friend’s velocity = train velocity ± walking speed, depending on walking direction.
  • Earth’s surface often used as default reference frame for day-to-day problems.

Distance vs. Displacement

  • Distance (d)
    • Total path length covered.
    • Scalar (magnitude only).
    • Question answered: “How much ground was covered?”
  • Displacement (\Delta x)
    • Straight-line change from initial to final position.
    • Vector (magnitude & direction).
    • Question answered: “How far and in what direction from start?”

Worked Example (Straight Line Walk)

  • Path: A \to C = 100\,\text{m}, \; C \to B = 30\,\text{m back}
  • Distance: d = 100\,\text{m} + 30\,\text{m} = 130\,\text{m}
  • Displacement: \Delta x = 100\,\text{m} - 30\,\text{m} = 70\,\text{m to the right}

Practice Problem (“TRY THIS!” – Football Coach)

  • Moves A→B→C→D with U-turns each time.
    • Students compute (a) total path length = sum of segment lengths, (b) net vector from A to D = displacement.

Speed vs. Velocity

  • Speed (s)
    • \displaystyle s = \frac{\text{distance}}{\text{time}}
    • Scalar; always non-negative.
  • Velocity (v)
    • \displaystyle v = \frac{\text{displacement}}{\text{time}} = \frac{x2 - x1}{\Delta t}
    • Vector; sign or arrow denotes direction.

Speed Worked Problems (Vendor & Cart)

  1. Pushes empty cart: d = 10\,\text{m},\; t = 5\,\text{s} → s = \frac{10}{5} = 2\,\mathrm{m/s}
  2. Pushes heavy cart at constant s = 1\,\mathrm{m/s},\; t = 15\,\text{s} → d = s t = 15\,\text{m}
  3. Pushes d = 30\,\text{m} at s = 0.5\,\mathrm{m/s} → t = \frac{30}{0.5} = 60\,\text{s} = 1\,\text{min}
  • Significance: Demonstrates inverse relationship between speed and travel time for fixed distance.

Velocity Worked Problems

  1. Marathon scenario
    • x1 = 5000\,\text{m},\; x2 = 4500\,\text{m},\; \Delta t = 90\,\text{s}
    • v = \frac{4500 - 5000}{90} = \frac{-500}{90} \approx -5.56\,\mathrm{m/s} (negative sign = backward relative to original running direction)
  2. Rolling ball (prompt only)
    • Given: x1 = 8.4\,\text{cm},\; x2 = -4.2\,\text{cm},\; \Delta t = 6.1\,\text{s}
    • Students to compute: v = \frac{-4.2 - 8.4}{6.1}\,\mathrm{cm/s} → v \approx -2.07\,\mathrm{cm/s}
  • Motion analysis requires distinguishing scalar vs. vector quantities.
  • Selection of reference frame affects numerical values of position, velocity, and even the qualitative description of motion.
  • Physics uses simplified models (straight-line motion, constant speed) to build intuition before addressing complex, real-world cases (accelerated, 2-D/3-D motion).
  • Quantitative problem-solving develops logical reasoning and math skills applicable across STEM fields.

Looking Ahead

  • Subsequent lessons likely cover acceleration, graphical analysis (d–t, v–t graphs), Newton’s laws, and energy concepts, linking back to the foundational definitions provided here.
  • Modern physics branches will revisit these core ideas in extreme regimes (relativistic speeds, quantum scales), showing continuity across the discipline.