A physics problem may give you five numbers and ask for a sixth.
That makes the task look simple:
find the correct equation, substitute the numbers, calculate the answer.
But this description hides most of the physics.
Before an equation can solve anything, someone has to decide what situation the equation is supposed to describe.
What is the object we are studying?
What belongs to the system?
What is interacting with it?
Which effects matter?
Which effects can reasonably be ignored?
What quantities describe the situation?
And what model connects them?
These decisions often happen so quickly in an expert’s mind that a beginner never sees them.
Then the beginner is shown:
F = ma
and physics appears to be a subject about formulas.
It is not.
The equation is only one stage in a much longer chain of reasoning.
Reality → system → relevant interactions → quantities → relationships → model → equation → prediction → test
That chain is where physics actually happens.
A Formula Cannot Tell You What the Problem Is
Imagine a box being pushed across a floor.
We know its mass. We know the applied force. We want to predict its acceleration.
It looks like a straightforward Newton’s second law problem.
But consider what has already been decided before we write an equation.
Are we studying the box alone?
The box and the floor?
The box and the Earth?
Does friction matter?
Does air resistance matter?
Is the floor horizontal?
Is the applied force horizontal?
Does the box remain in contact with the floor?
Are we treating the box as a particle, or does its shape and rotation matter?
The physical world has not changed.
But our description of the world depends on what we are trying to understand.
That distinction is fundamental.
Physics does not simply hand us a ready-made problem.
We construct a manageable representation of reality and then reason within it.
The First Decision: What Is the System?
One of the most powerful questions in physics is also one of the simplest:
What are we studying?
Suppose a person pushes a box.
If the system is the box, the push from the person is an external interaction.
If the system is the person and the box together, that same interaction becomes internal to the chosen system.
Nothing magical happened to the force.
We changed the boundary through which we were looking at the situation.
This is why identifying the system is not a decorative step in a textbook solution.
It changes the structure of the problem.
The same reality can support different valid models because we may be asking different questions about it.
Relevant Does Not Mean “Everything That Exists”
Real situations contain enormous amounts of information.
A moving car has a color.
The road has a temperature.
Earth is rotating.
The Moon is exerting a gravitational force.
Individual molecules in the tires are moving.
All of those statements may be true.
But truth alone does not make a fact useful for a particular calculation.
Physics requires another ability:
deciding what matters at the scale of the question.
For many introductory motion problems, the color of the car is irrelevant.
For a thermal-radiation problem, color or surface properties may suddenly matter.
Air resistance may be negligible when analyzing one situation and essential in another.
The skill is therefore not merely knowing more facts.
It is knowing which facts the model needs.
That is a much deeper form of understanding.
Ignoring Something Can Be Scientifically Correct
Students are sometimes uncomfortable when physics tells them to “neglect air resistance” or “assume a frictionless surface.”
It can sound as though the problem is asking them to pretend reality is different from what it is.
But a model is not necessarily false because it leaves something out.
A model is useful when it preserves the features needed to answer a particular question with an acceptable level of accuracy.
Consider a ball falling from a modest height.
For one question, treating gravitational acceleration as constant may be entirely adequate.
For another question involving a spacecraft over enormous distances, the same approximation may be inadequate.
So the real question is not:
Is the model perfectly identical to reality?
No model is.
The better question is:
Is this model adequate for the prediction we are trying to make?
That is scientific judgment.
What F = ma Does — and Does Not — Give You
Newton’s second law is extraordinarily powerful.
But the expression
F = ma
does not independently tell you:
what object to analyze,
which forces act on it,
which coordinate system to choose,
whether acceleration is constant,
whether a force can be neglected,
or whether Newtonian mechanics is even an adequate framework for the situation.
Those decisions come first.
Only then can the equation connect the quantities inside the chosen model.
This explains a familiar classroom puzzle.
A student may remember the equation perfectly and still be unable to solve the problem.
The missing knowledge is not necessarily another formula.
The student may be struggling one level earlier:
constructing the physical situation from the information given.
A Physics Problem Is Actually Several Problems
What appears on paper as one exercise often contains several different intellectual tasks.
First, there is the real or described situation.
Then comes interpretation:
What is happening?
Then selection:
What matters?
Then representation:
Can the situation be expressed with a diagram, variables, vectors, a graph, or another model?
Then comes mathematical reasoning.
Finally, the result has to return to the physical world:
Does this answer make sense?
A calculation can be algebraically flawless and physically absurd.
If a solution predicts that an ordinary bicycle accelerates from rest to several times the speed of sound in two seconds, completing the arithmetic is not enough.
The result itself becomes evidence.
Physics asks us to compare the prediction with the world the model was supposed to describe.
Prediction Is Where the Model Becomes Accountable
A model is not valuable merely because it looks elegant.
It must do something.
It should help us explain observations, calculate consequences, or predict what will happen under specified conditions.
That gives us a powerful sequence:
observe → define → simplify → model → predict → compare
And sometimes the comparison fails.
That failure matters.
Perhaps the measurement is wrong.
Perhaps the calculation is wrong.
Perhaps an important interaction was neglected.
Perhaps the assumptions were inappropriate.
Or perhaps the model itself has reached the limits of where it works.
Scientific thinking does not require us to defend a model forever.
It requires us to know what the model claims, under what conditions, and when reality gives us a reason to revise it.
The Same Situation Can Produce Different Correct Questions
Imagine a car moving along a road.
One student may investigate its acceleration.
Another may calculate the energy required to increase its speed.
Another may study friction between the tires and the road.
Another may analyze heat produced during braking.
Another may investigate air resistance.
There is only one car.
But there is no single compulsory description of the car that contains “the physics problem.”
The question determines which relationships become relevant.
This is an important intellectual shift.
A phenomenon and a model of that phenomenon are not the same thing.
Representation ≠ phenomenon.
The diagram is not the car.
The equation is not the motion.
The graph is not time.
They are tools that allow particular relationships to become visible.
Why Students Sometimes “Know Physics” but Cannot Solve Physics Problems
A student can know definitions.
A student can remember equations.
A student can reproduce a worked example.
And still freeze when the surface details of the next problem change.
This often happens because the student learned the representation without fully learning the decision process that produced it.
If every familiar problem already arrives with the correct equation nearby, the learner is practicing calculation.
But real problem solving begins when the equation is not supplied.
The learner has to move from:
What formula do I need?
to:
What is happening here, and how can I represent it?
That change is enormous.
It transforms physics from formula retrieval into model building.
This Is Also Why Language Matters in Physics
Physics is often presented as though mathematics eliminates the need for language.
It does not.
Before students can calculate, they frequently have to interpret words such as:
constant, relative, uniform, net, average, instantaneous, isolated, negligible, proportional, at rest, with respect to.
These are not decorative words surrounding the mathematics.
They constrain the model.
Compare:
The car is at rest.
with:
The car is at rest relative to the train.
The second statement defines a reference relationship that the first may leave implicit.
Or compare:
a force
with:
the net force.
Those expressions do not identify the same physical quantity.
Understanding the language of a problem is therefore part of understanding its physics.
This becomes especially important when students study physics in English or another language that is not their first.
They are not merely translating vocabulary.
They are learning how a scientific problem encodes relationships through language.
Learning Physics Through Another Language Can Reveal the Thinking
Studying a subject through another language creates an interesting difficulty.
What was previously automatic may become visible.
A student has to distinguish between:
speed and velocity,
mass and weight,
distance and displacement,
force and net force.
That can initially slow the learner down.
But when handled properly, the difficulty can become productive.
The learner is forced to examine distinctions that may have been blurred by familiarity.
This is one reason we treat Language + Subject as its own educational layer at Levitin Language School.
The purpose is not to replace physics with an English lesson.
Nor is it to attach vocabulary exercises to a physics textbook.
The subject remains real.
The physics has to work.
The language becomes one of the tools through which the learner observes, distinguishes, explains, and reasons about the subject.
A Better Question Than “Which Formula?”
When facing an unfamiliar physics problem, try delaying the search for an equation.
Ask instead:
- What phenomenon is being described?
- What exactly am I trying to predict or explain?
- What is my system?
- What interacts with it?
- Which quantities are relevant?
- What can I reasonably neglect?
- What assumptions am I making?
- Which model expresses these relationships?
- What does the model predict?
- Does that prediction make physical sense?
Only somewhere in the middle of that process does the familiar formula appear.
And now it has a job.
Physics Is the Art of Building a Useful Version of Reality
Physics does something intellectually remarkable.
It begins with a world that is overwhelmingly complicated and constructs a representation simple enough to reason with — but rich enough to preserve what matters.
That requires knowledge.
But it also requires selection.
Perspective.
Approximation.
Testing.
And judgment.
A formula can compress a relationship into a few symbols.
It cannot decide which part of reality deserves those symbols.
That decision belongs to the person doing the physics.
So before solving the next physics problem, do not begin by asking:
Which equation should I use?
Begin one step earlier:
What problem am I actually solving?
That is where physics begins.
Continue Exploring
Physics Is Not the Subject. Thinking Is.
Language Thinking Lab
https://languagethinkinglab.blogspot.com/2026/05/physics-is-not-subject-thinking-is.html
This is the conceptual starting point for the broader connection between physical reasoning, explanation, and language.
Learn Physics in English, German or Spanish
https://timurlevitin.blogspot.com/p/learn-physics-in-english-german-or.html
For students who want to study physics while developing the language they use to understand and explain it.
Learn Languages Through School Subjects
https://timurlevitin.blogspot.com/p/learn-languages-through-school-subjects.html
Explore the broader Language + Subject approach across academic disciplines.
Learn English Through Math and Science
https://timurlevitin.blogspot.com/p/learn-english-through-math-and-science.html
A route for learners who want English to become a working language for academic reasoning rather than an isolated school subject.
About the Author
Tymur Levitin
Founder & Director, Levitin Language School / Language Learnings
Levitin Language School develops individual online learning across languages, academic subjects, and Language + Subject combinations.
Main website: https://levitintymur.com
Language Learnings: https://languagelearnings.com
© 2026 Tymur Levitin. All rights reserved.
