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 ($v$)
  • $\displaystyle v = \frac{\text{displacement}}{\text{time}} = \frac{x<em>2 - x</em>1}{\Delta t}$
  • 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
   • $x<em>1 = 5000\,\text{m},\; x</em>2 = 4500\,\text{m},\; \Delta t = 90\,\text{s}$
   • $v = \frac{4500 - 5000}{90} = \frac{-500}{90} \approx -5.56\,\mathrm{m/s}$ (negative sign = backward relative to original running direction)
2. Rolling ball (prompt only)
   • Given: $x<em>1 = 8.4\,\text{cm},\; x</em>2 = -4.2\,\text{cm},\; \Delta t = 6.1\,\text{s}$
   • Students to compute: $v = \frac{-4.2 - 8.4}{6.1}\,\mathrm{cm/s}$ → $v \approx -2.07\,\mathrm{cm/s}$

Key Takeaways & Conceptual Links

• 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.