Expert knowledge I

Welcome to the Expert level.

At this point, you understand how objects move and what causes that motion. You’ve described motion with precision and explained it using Newton’s Laws. Now it’s time to go deeper—to uncover why certain physical processes happen and what limits them.

In this unit, you’ll explore one of the most powerful and unifying concepts in all of physics: energy.

1. What Is Energy?

Energy is the capacity to do work or produce change.
It’s not a thing you can see or touch, but it’s present in everything—from falling objects to orbiting planets to vibrating atoms.

Energy appears in many forms:

• Kinetic energy (motion)

• Potential energy (position in a field, like gravity or a spring)

• Thermal energy (random motion of particles)

• Chemical, electrical, nuclear, and more

Despite these different forms, energy always follows one rule: it is conserved.

2. The Law of Conservation of Energy

This is one of the most fundamental principles in physics:

Energy cannot be created or destroyed. It can only be transformed from one form to another.

This means that in any closed system, the total energy stays the same. It may move between objects or shift forms—but it never disappears.

Example:
When a ball is dropped, its gravitational potential energy is converted into kinetic energy as it falls. The total amount of energy remains constant.

3. Kinetic and Potential Energy – A Deeper Look

• Kinetic energy (KE) is energy of motion:

  KE=12mv2KE = \frac{1}{2}mv^2KE=21​mv2

• Gravitational potential energy (PE) near Earth’s surface:

  PE=mghPE = mghPE=mgh

Where:

• m = mass (kg)

• v = velocity (m/s)

• g = gravitational acceleration (9.81 m/s²)

• h = height (m)

In many systems, energy shifts back and forth between KE and PE—like in a pendulum or roller coaster. At the top: all PE. At the bottom: all KE.

4. Work – The Bridge Between Force and Energy

Work is how forces transfer energy.
In physics, work has a specific definition:

Where:

• W = work (in joules)

• F = force applied

• d = displacement

• θ = angle between force and displacement

If the force and displacement are in the same direction, the full force contributes to work.

No displacement = no work, no matter how much effort you feel you’ve used. (Sorry, pushing a wall counts as exercise—but not work in physics!)

5. Why This Matters

Energy explains why things move, how systems interact, and where limits lie. It connects all branches of physics: mechanics, thermodynamics, electricity, quantum physics, and cosmology.

You’re now beginning to see the universe in terms of energy flows and transformations—a perspective that will deepen with every unit.

In this unit, you’ve learned:

• What energy is and how it appears in different forms

• That energy is conserved in all physical processes

• How to calculate kinetic and potential energy

• How work relates force and energy transfer

These concepts allow you to analyze systems even when forces are complicated or unknown—by tracking energy instead.

In the next unit, we’ll introduce mechanical energy conservation, non-conservative forces, and the idea of energy loss (think friction and heat).

You’ve just completed your first Expert unit—congratulations!
You’ve explored energy as a powerful, abstract concept that connects motion, forces, and deeper physical principles. That’s a big leap, and it shows how far you’ve come in your physics journey.

Now it’s time to pause and reflect:

• Did this unit make sense to you overall, even if it was challenging?

• Were you able to follow the equations and concepts about energy, work, and conservation?

• Do you feel motivated to continue learning at this level?

Remember: it’s perfectly okay to adjust your pace. The most important thing is that you feel confident and supported in your learning.

Choose your next step:

• 🔁 I'd prefer to return to the Advanced level to strengthen my foundation before continuing.

• 🚀 I'm ready to stay in the Expert track and continue building on these concepts.

There’s no pressure. Everyone’s learning path is different, and physics is a subject that rewards patience, curiosity, and persistence. You’ve already made great progress—keep going your way!