Physics: The Hidden Knowledge That Breathes

A little game before we start 👇 right now, take the phone you’re reading this on and hold it up. Its screen emits light (optics and semiconductor), it stays in your hand and doesn’t fall because a force holds it (mechanics), a little bit of movement makes it heat up (thermodynamics 🥵), and once you’re online a bunch of invisible waves carry your message across the world (electromagnetism). One object, four big branches of physics. Now count how many bits of “physics” are hidden in an ordinary house… 😏

Where is physics? Everywhere, just silent 🤫

Look, you don’t have to dive into black holes or giant accelerators to find physics’s footprints. Physics is right next to your ear, so close you don’t even notice it. The refrigerator, the car, the light, the elevator, even that cup of tea steaming ☕ — each is a bright, working physics classroom. Here’s a funny point 😅 we usually notice physics when it’s broken! As long as everything is in place, it’s invisible. When a car brakes, you don’t think about friction; you only think about it when the road is icy and the car starts sliding like a skater 🛷😬. What does that mean? It means physics is the science of the very laws the silent universe follows — whether we pay attention or not.

A scope that blows the mind 🤯

One of the coolest things about physics is that its scale can’t be grasped with ordinary intuition. Physicists go after both the ultra‑tiny and the ultra‑huge — and, oddly enough, they often do it with the same handful of laws! On one side there are particles like quarks and electrons that are so small that even the word “small” feels too big for them 😶. On the other side, there are galaxies whose light must travel millions of years to get from one end to the other. So what sits in the middle of this vast spectrum? You, right there! 🧍Exactly in the middle of the universe’s scale. It’s no accident that it feels hard; our brains are built to understand distances like “cave to river,” not “atom to galaxy” 😄.

But physics isn’t about “memorizing laws” ☝️

Here’s the most important point of this lesson, and I wish everyone started here: a physicist isn’t someone who parrots laws 🦜. A physicist is someone who looks at natural phenomena, searches for patterns and order, and then tries to explain that order with precise language. Their toolbox has three items: law, model, and theory. And because physics is an experimental science, none of these three have any real value until they’ve been tested against experiment. Now comes the part that usually makes kids raise their eyebrows 🫢:

Physics laws and theories are not eternal and untouchable!

No, no, this isn’t a weakness of physics, it’s actually exactly strength 💪. Every theory in physics makes a promise: “If you do such-and-such experiment, you’ll get such-and-such result.” Now if one day an experiment gives a different result, the theory must be set aside and changed — and that’s happened many times. Science that is ready to say “I was wrong” is the science that can grow 🌱. (In the philosophy of science this is called falsifiability; that is, a scientific claim must be such that you can imagine an experiment that would refute it. If no experiment could refute it, it’s not science, just a pretty statement 😅.)

🔬 The best example of modeling in the history of science: the atomic model — which has been rewritten five times in 120 years. The full story with a table of models is waiting for you in the modeling section ⚛️.

Galileo and that famous Leaning Tower of Pisa experiment 🪶🔨

Let’s go to the moment that could be said to mark the birth of modern experimental physics. For centuries everyone thought Aristotle was right: a heavier object falls faster. It sounds logical, right? 🤔 A stone reaches the ground before a feather. But Galileo did a seemingly simple yet revolutionary thing: instead of sitting and debating or saying “Aristotle said it!”, he said “Let’s test it, man 🤷.” The famous story says he dropped two objects, a light one and a heavy one, from the top of the Leaning Tower of Pisa to see whether they hit the ground at the same time. (Historically there’s some doubt that he actually performed this from the tower, but the spirit of the story is correct: it was Galileo who realized only an experiment could answer.) The result he got is one of the most beautiful statements in physics:

The acceleration of a falling object has nothing to do with its mass! 😲

It means that if you remove air resistance, a feather and a hammer will hit the ground at the same time. It’s so contrary to intuition that the Apollo 15 astronauts actually tested this on the Moon (which has no air) with a feather and a hammer 🪶🔨 — and both landed together on the lunar surface! Galileo, four hundred years earlier, had reached this conclusion just by thinking about it. He wasn’t the only one 😎.

🪶🔨 Watch this video: David Scott, Apollo 15 astronaut, in 1971 released a feather and a hammer simultaneously on the Moon’s surface. There’s no air, so no resistance — and both reach the ground together. Galileo had arrived at this just by thinking about it four hundred years earlier 🤯.

The lesson Galileo gave us wasn’t just about falling objects; it was about the method: when you want to know what nature says, ask nature itself, not old textbooks 📚🚫.

More important than the experiment: a curious and critical mind 🕵️

Here is a subtle point that the textbook correctly mentions and many overlook. Experiment and observation are the lifeblood of physics — but what has propelled science more than anything is not empty experiment; it’s critical thinking and active mental curiosity 🧠. Why? Because experiment alone only gives you a number. It’s that critical mind that asks: “Well, what does this number mean? What does it ignore? What assumption lies behind it? Could there be a simpler way to explain it? 🤨” Thousands of people before Galileo had also seen objects fall; the difference was that Galileo questioned what he saw and asked the right question. So if you want to take just one habit from this lesson, it’s: instead of memorizing the answer, learn to ask good questions ✨.

Physics, the foundation of every engineering 🏗️

One final point that clarifies the role of this lesson. No engineering can be done without understanding the basic laws of physics. Flat‑screen TVs, energy‑saving lamps, interplanetary spacecraft, bridges, dams, drones, MRI machines — all of them rest on physics. That’s why we call it fundamental knowledge: not because it’s above other sciences, but because it’s the groundwork. When the foundation is solid, you can build anything on it 🧱.

The “Interesting to Know” Box 💡

Where does the word “physics” come from? Its root is ancient Greek and means “knowledge of nature.” Greek philosophers from the 7th century BC were the first to ask serious questions about nature. Later Muslim scientists — especially Iranians such as Abu Rihān Biruni, Ibn Sīnā, Ibn Al‑Haytham and Khāje Nasir‑al‑Din Tūsī — in astronomy, optics, and mechanics expanded this knowledge so that it later became the foundation for Galileo’s work and others. Now a cool thing 😎: many consider Ibn Al‑Haytham the “father of the scientific method”; he argued hundreds of years before Galileo that “a claim must be tested by experiment!”

Test yourself 📝

👇 Click on each question to reveal the answer — first try to answer it yourself!

۱ Why do we say that changes in physics theories are a sign of the strength of science, not its weakness? 🤔 👆 Click to see the answer

When theories change, it means science updates itself with new evidence. If a theory were eternal and never revised, it wouldn’t be science but a

3 If your friend says “Heavier objects always fall faster”, how can you show with a simple experiment (and paying attention to the role of air) that this isn’t true? 🪶 👆 Click to see the answer

Simple experiment: crumple a sheet of paper and take a flat sheet (both have the same mass!) and drop them at the same time. The crumpled one reaches the ground first. If mass mattered, they would land together. So air resistance is the cause of the difference, not mass. In a vacuum (the classic Galilean coin drop experiment) both reach the ground simultaneously.

4 Find three items in your home and for each say which branch of physics plays the main role. 🏠 👆 Click to see the answer

Examples (you can add other examples as well):

5 What is falsifiability? Give an example of a “scientific” claim and

Remember we said our brain is built for “cave to river”, not “atom to galaxy”? Let Python draw this scale for us so we can really feel it:

import numpy as np
import matplotlib.pyplot as plt

objects = [
    (-18, "Quarkn~10⁻¹⁸ m"),
    (-15, "Protonn~10⁻¹⁵ m"),
    (-10, "Atomn~10⁻¹⁰ m"),
    (-7,  "Virusn~10⁻⁷ m"),
    (-3,  "Antn~10⁻³ m"),
    (0,   "YOUn~1 m"),
    (4,   "Mt. Everestn~10⁴ m"),
    (7,   "Earth diametern~10⁷ m"),
    (11,  "Earth-Sunn~10¹¹ m"),
    (16,  "Our galaxyn~10¹⁶ m"),
    (26,  "Observablenuniverse"),
]

fig, ax = plt.subplots(figsize=(13, 3.5))
ax.axhline(0, color='#2c3e50', linewidth=2.5)

for i, (lp, label) in enumerate(objects):
    color = '#e74c3c' if 'YOU' in label else '#3498db'
    size  = 200 if 'YOU' in label else 100
    ax.scatter(lp, 0, s=size, color=color, zorder=5)
    offset = 0.55 if i % 2 == 0 else -0.65
    ax.annotate(label, (lp, 0), xytext=(lp, offset),
                ha='center', va='center', fontsize=7.5,
                arrowprops=dict(arrowstyle='-', color='gray', lw=0.5))

ax.set_xlim(-21, 28)
ax.set_ylim(-1.3, 1.3)
ax.set_xlabel('Power of 10 (meters) — each step = x10', fontsize=9)
ax.set_title('Scale of the Universe — from quarks to the observable universe', fontsize=12, fontweight='bold')
ax.set_yticks([])
ax.set_xticks(range(-20, 28, 5))
ax.grid(axis='x', alpha=0.3)
plt.tight_layout()
plt.savefig('scale_of_universe.png', dpi=120, bbox_inches='tight')
plt.show()

💡 Note: Each step on the axis means times 10! From you (the red dot) to the atom: 10 steps to the left. From you to the galaxy: 16 steps to the right. Our brain is designed for a few steps — not a 44‑step range!

2. Galileo’s experiment — Does mass really matter? 🪶🔨

The famous claim: In a vacuum, a feather and a hammer fall together. Let’s see:

import numpy as np
import matplotlib.pyplot as plt

g = 9.8    # gravitational acceleration (m/s²)
h = 40.0   # drop height (m)

# ── Vacuum: both objects identical ─────────────────────────────
t_vac = np.sqrt(2 * h / g)
t = np.linspace(0, t_vac, 300)
y_vac = h - 0.5 * g * t**2

# ── With air resistance: step-by-step simulation ───────────────
def free_fall(mass_kg, drag_coef=0.04):
    dt, y, v, ts, ys = 0.002, h, 0.0, [0], [h]
    while y > 0:
        a = -g + (drag_coef / mass_kg) * v**2
        v += a * dt; y += v * dt
        ts.append(ts[-1] + dt); ys.append(max(y, 0))
        if y <= 0: break
    return np.array(ts), np.array(ys)

t_light, y_light = free_fall(0.05)   # 50 g (like crumpled paper)
t_heavy, y_heavy = free_fall(1.0)    # 1 kg (like a can)

fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(11, 4.5))

ax1.plot(t, y_vac, 'b-', lw=2.5, label='Any object — mass does not matter!')
ax1.set_title('In vacuum — Galileo was right', fontweight='bold')
ax1.set_xlabel('Time (s)'); ax1.set_ylabel('Height (m)')
ax1.legend(); ax1.grid(alpha=0.4)

ax2.plot(t_light, y_light, 'r--', lw=2, label='50 g (light)')
ax2.plot(t_heavy, y_heavy, 'g-',  lw=2, label='1 kg (heavy)')
ax2.set_title('With air resistance — mass matters!', fontweight='bold')
ax2.set_xlabel('Time (s)')
ax2.legend(); ax2.grid(alpha=0.4)

plt.suptitle("Galileo's Experiment — vacuum vs. air", fontsize=13, fontweight='bold')
plt.tight_layout()
plt.savefig('galileo_fall.png', dpi=120, bbox_inches='tight')
plt.show()

🤓 Challenge: Change drag_coef to 0.0 — both become like in a vacuum. Then try 0.4 (like a flat piece of paper). See when the system “breaks”.

Resources and Further Reading 📚

Wikipedia

Video — YouTube 🎬

Video — Aparat 🎬

Simulator

On this site 🔗

In the next section, we’ll move on to one of the most important tools of physics: modeling — the art of intelligently simplifying the world so that it can be understood. See you! 👋

Have a question? 🤔

If something isn't clear or you have a question, ask it here. The answer will be published on this page.

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