From Baking Soda to Conservation Laws: Connecting Simple Experiments to Big Ideas
🔄 The Deeper Pattern
Your students see vinegar and baking soda fizz. Feynman saw one of nature's most profound principles: conservation. Every simple experiment in your classroom is a window into the unchanging laws that govern the universe.
When middle schoolers mix vinegar and baking soda, they see fizzing, bubbles, and an inflating balloon. Fun! But according to Feynman, they're also witnessing something profound: the law of conservation. Not just conservation of mass, but a pattern that appears everywhere in nature. Here's how to help students see the bigger picture.
What Is Conservation?
Feynman explained conservation with a beautiful analogy: Imagine a child has 28 indestructible blocks. His mother counts them every day and always finds 28. One day she finds only 26 blocks visible. She looks out the window and sees 2 blocks on the lawn: 26 + 2 = 28. The next day she finds only 25 blocks, but the toy box feels heavier. She realizes she can create a formula:
(Blocks seen) + (Extra weight of box ÷ weight per block) = 28
Energy is like those blocks. It's not a "thing"—it's a number we calculate. And the remarkable discovery is that this number stays constant. Energy can transform into different forms (kinetic, potential, heat, chemical), just like the blocks can be hidden in different places, but the total never changes.
Feynman's Key Insight About Conservation:
"There is a fact, or if you wish, a law, governing all natural phenomena that are known to date. There is no known exception to this law—it is exact so far as we know. The law is called the conservation of energy. It states that there is a certain quantity, which we call energy, that does not change in the manifold changes which nature undergoes."
Conservation Laws in Your Experiments
Every experiment you already teach demonstrates conservation. The question is: Are your students seeing it? Let's connect your hands-on activities to these profound principles.
1. Conservation of Mass: The Baking Soda Reaction
When students mix vinegar and baking soda in an open cup, they see fizzing and bubbling. The mixture gets lighter. It looks like mass disappeared. But did it?
The Feynman-Style Investigation:
Setup 1: Open System
• Weigh vinegar + baking soda before mixing: Let's say 100g
• Mix them in an open cup
• Weigh the mixture after: Maybe 95g
• Question: Where did the 5g go?
Setup 2: Closed System
• Put vinegar + baking soda in a bottle with a balloon over the top
• Weigh the whole system before: 100g
• Mix (balloon inflates with CO₂)
• Weigh the whole system after: Still 100g!
• Insight: The mass didn't disappear—it just turned into gas and escaped in the open system.
This is conservation of mass in action. Atoms don't disappear—they just rearrange. In your closed system, you can prove it.
Discussion Questions (Feynman Style):
• "Where did the missing mass go in the open cup?"
• "How do we know atoms didn't actually disappear?"
• "What would happen if we could weigh the air above the open cup—would we find the missing mass?"
Let students reason through it. The answer is more memorable when they figure it out.
2. Conservation of Energy: The Pendulum
A simple pendulum demonstrates one of physics' most beautiful principles: energy transforming between kinetic (motion) and potential (position), but the total staying constant.
The Feynman-Style Activity:
Materials: String, heavy washer or weight, tape, meter stick
Setup: Hang a pendulum from the ceiling or a doorframe. Pull the weight to your nose level, hold it still, then release it without pushing.
The Prediction:
"Will the pendulum swing back and hit me in the face? Make your prediction and explain why."
The Result:
The pendulum swings away, comes back, and stops just short of your nose—every single time.
The Explanation (Build Together):
• At the top: All potential energy, no motion
• Swinging down: Potential energy converts to kinetic (motion) energy
• At the bottom: All kinetic, no potential
• Swinging back up: Kinetic converts back to potential
• Returns to original height: Can't go higher because energy is conserved!
It can't hit your face unless you gave it more energy by pushing it.
This demonstration is dramatic and safe (start with a short release if you're nervous!). Students see conservation of energy protecting you from being hit. The law isn't abstract—it's keeping you safe.
3. Conservation of Momentum: Balloon Rockets
Newton's third law (action-reaction) is really about conservation of momentum. When one thing gains momentum in one direction, something else must gain equal momentum in the opposite direction.
The Balloon Rocket Experiment:
Setup: Thread a string through a straw, stretch it across the room, inflate a balloon, tape it to the straw, release.
What Students See:
Air rushes backward (out the balloon opening), balloon zooms forward.
The Conservation Principle:
Before release: Total momentum = 0 (nothing moving)
After release: Air molecules move backward with momentum, balloon moves forward with momentum
The sum still equals 0! Forward momentum exactly cancels backward momentum.
This is conservation of momentum. The total never changes.
Real rockets in space work the same way. They shoot exhaust backward (momentum in one direction), which pushes the rocket forward (momentum in the other direction). Conservation of momentum makes space travel possible.
Why Conservation Laws Matter: Feynman's Perspective
Feynman emphasized that conservation laws are the deepest principles in physics. They're not just "rules"—they're connected to the fundamental symmetries of nature.
The Deep Connection (For Your Reference)
Conservation of Energy ↔ The laws of physics don't change with time
Conservation of Momentum ↔ The laws of physics are the same everywhere in space
Conservation of Angular Momentum ↔ The laws of physics don't depend on which direction you face
(You don't need to teach this connection in middle school, but it's fascinating to know that conservation laws emerge from the symmetries of the universe!)
Teaching Conservation: The Feynman Framework
Here's how to structure any lesson around conservation:
Step 1: Set Up the Accounting System
"We're going to track something—mass, energy, or momentum. Let's measure how much we start with."
Step 2: Let Something Happen
Run the experiment. Let the reaction happen, the pendulum swing, the balloon fly.
Step 3: Check the Books
"Now let's measure again. Did the total change? If it looks like it changed, where did it go or come from?"
Step 4: Find the Missing Pieces
"If we can't find the missing energy/mass/momentum, we haven't looked hard enough. It's there somewhere."
Common Student Misconceptions About Conservation
❌ "Energy gets used up"
✅ Energy transforms but never disappears. A battery doesn't "run out of energy"—its chemical energy converts to electrical, heat, and light energy. The total is conserved.
❌ "The pendulum stops because energy disappears"
✅ The energy converts to heat (from air resistance and friction at the pivot). It's still there—just spread out as thermal energy in the air and string.
❌ "Heavier objects fall faster because they have more energy"
✅ All objects fall at the same rate (ignoring air resistance). But yes, heavier objects do have more energy when they hit the ground—that's why a falling car is more dangerous than a falling apple.
❌ "Heat isn't real energy"
✅ Heat is the random motion energy of atoms. It's just as real as the motion energy of a thrown ball— but spread out among trillions of tiny particles instead of concentrated in one object.
Making Conservation Visual: The Energy Chain Game
Feynman loved making abstract concepts concrete. Here's an activity that makes energy transformations visible:
Energy Chain Activity
Setup: Give students a starting scenario: "You eat a banana."
Challenge: Trace the energy transformations as far back and as far forward as you can.
Backward Chain (Where did the energy come from?):
Banana's chemical energy ← Grew from sunlight ← Nuclear reactions in the Sun ← Gravitational energy from hydrogen atoms falling together billions of years ago
Forward Chain (Where does the energy go?):
You digest banana → Chemical energy in your cells → You run (kinetic energy) → You stop (heat energy warms your body and air) → Eventually radiates into space as infrared light
The Point: Energy never appears or disappears—it just transforms and moves around. Your breakfast's energy originally came from the Big Bang and will eventually become heat radiating into space. Conservation connects everything.
From Simple Experiments to Universal Principles
This is what Feynman wanted teachers to understand: Your simple experiments aren't "just demos." They're windows into the deepest truths about how the universe works.
When students mix baking soda and vinegar, they witness conservation of mass. When they watch a pendulum, they see conservation of energy. When they launch a balloon rocket, they experience conservation of momentum.
These aren't separate facts to memorize. They're all manifestations of the same principle: Nature keeps perfect accounts. Nothing is ever truly created or destroyed—it just transforms and moves around.
The Feynman Question to Ask Every Time
After any experiment where something seems to appear, disappear, or change:
"Where did it come from, and where did it go?"
This simple question trains students to think in terms of conservation. Nothing appears from nowhere. Nothing vanishes into nothing. If you can't find it, you haven't looked carefully enough.
The Bottom Line
Feynman said: "There is no known exception to this law—it is exact so far as we know."
Conservation laws are among the most certain things we know about the universe. They've been tested in every experiment ever conducted, from chemistry labs to particle accelerators to observations of distant galaxies. They always hold.
When you teach conservation, you're not teaching "a science topic." You're teaching students that the universe follows rules—reliable, unchanging, beautiful rules. That's empowering. It means the world is knowable and predictable.
Your students mix vinegar and baking soda. But with Feynman's guidance, they can see something profound: the universe keeping perfect track of every atom, every joule of energy, every bit of momentum. That's the real lesson.
Try This Next Week
- Pick one experiment and explicitly "do the accounting"—measure the total before and after, discuss where any "missing" quantity went.
- Ask the Feynman question at least once per experiment: "Where did it come from, and where did it go?"
- Do the Energy Chain activity with any everyday scenario—eating, driving, turning on a light—and trace the transformations as far as students can imagine.
Published on February 5, 2026 • 11 min read