Frequently asked questions

Start with Measurement & Math Tools, then Kinematics and Newton's Laws. Filter topics by the Beginner level and use the labs to see ideas in motion.

Beginner topics need arithmetic, basic algebra and graphs. Intermediate topics add trigonometry, vectors and basic calculus. Advanced topics use differential equations, linear algebra and complex numbers.

Mass is the amount of matter and is the same everywhere. Weight is the gravitational force on that mass (W = mg), so it changes with location.

Gravitational force grows with mass, but so does inertia. The two cancel, so every object accelerates at g in a vacuum.

Speed is how fast; velocity is how fast and in which direction. Velocity is a vector.

It is a fictitious force that appears in rotating frames. In an inertial frame, only the inward centripetal force is needed for circular motion.

Temperature measures the average kinetic energy of particles. Heat is energy transferred because of a temperature difference.

There are overwhelmingly more disordered microstates than ordered ones, so isolated systems almost certainly evolve to higher entropy.

DC flows in one direction. AC reverses direction periodically, which makes transformers and long-distance power transmission practical.

Changing electric fields create magnetic fields and vice versa. Maxwell's equations unify them and predict electromagnetic waves, including light.

Both. Light shows interference and diffraction like a wave, and the photoelectric effect and Compton scattering like a particle. Quantum theory unifies both.

It is a fundamental limit on knowing certain pairs, like position and momentum, simultaneously. It is not a flaw in measuring instruments.

Reaching c would need infinite energy for anything with mass, and causality would break if signals travelled faster than c.

A region where gravity is so strong that nothing, not even light, can escape beyond the event horizon.

Unseen matter whose gravity explains galaxy rotation and lensing. Its nature is still unknown.

Fission splits heavy nuclei; fusion joins light nuclei. Both release energy because they move toward higher binding energy per nucleon.

Air molecules scatter short wavelengths far more than long ones (Rayleigh scattering, ∝ 1/λ⁴), so scattered blue light reaches your eyes from all directions.

Draw a diagram, list knowns and unknowns, choose the principle (Newton, energy, momentum), solve symbolically, then check units and whether the answer is plausible.

Carry units through every step. If both sides of an equation do not have matching dimensions, there is an error.

Quizzes give instant feedback after every question and are for learning. Tests are timed, show results only at the end and save your score history.

Yes, in your browser's local storage: completed topics, bookmarks, quiz stats and test history. Nothing is sent to any server.

Use the search box at the top or press / from any page. It searches topics, formulas, labs, FAQs and areas.

Simulations where you change parameters with sliders and watch the animation and graph update live. Each topic links to a relevant lab.

An inverse-square force produces conic-section orbits. Bound orbits are ellipses with the Sun at one focus.

Momentum is conserved in both. Kinetic energy is conserved only in elastic collisions.

When a periodic driving force matches a system's natural frequency, energy transfers efficiently and amplitude grows large.

Accuracy is closeness to the true value; precision is how tightly repeated measurements agree.

Yes in principle, but for large objects wavelengths are tiny and decoherence hides quantum effects, so classical physics works well.

The third law of thermodynamics shows removing the final bits of entropy would need infinitely many steps.

Research, engineering, data science, medicine and medical imaging, finance, energy, aerospace, electronics and education.

Typically quantum mechanics, general relativity and statistical mechanics, because they need new concepts and more mathematics. Build up gradually through the Intermediate level.

The topics, simulations, quizzes and tests are available in the app. Progress is saved in your own browser, so there is no sign-up step.

No. Progress, bookmarks and preferences are stored in your browser's local storage on the device you use, so they stay on that device.

If you are new to physics, start with Beginner topics in Measurement & Math Tools and Kinematics. Move to Intermediate once you can solve one-step problems with formulas and units, and to Advanced when you are comfortable with calculus and vectors.

Yes, as a companion resource. It explains concepts and provides practice, but it is not an official syllabus, and it does not replace your course textbook or your instructor's guidance.

Yes. The layout adapts to small screens, and the simulations and quizzes can be used on touch devices.

Use the search box in the header or press the forward slash key to jump to it. You can search by topic name, formula or keyword, such as Ohm's law or escape velocity.

Anyone learning physics, from school students and university undergraduates to self-taught learners and adults returning to the subject. Each topic is tagged Beginner, Intermediate or Advanced so you can pick a suitable starting point.

Read the plain-language explanation first, then the key formula and worked example. Try the common-mistake note yourself before reading the full steps, and finish with the uses and FAQs to connect the idea to the real world.

Yes for the early areas, which use arithmetic, simple algebra and graphs. Later areas add trigonometry, vectors and calculus, and the topic pages explain each new tool as it appears.

No. The simulations show how a model behaves and help you see the effect of changing a variable. Real experiments are still essential for learning how measurements behave in practice.

Topic pages are static, crawlable explanations that you can read or share. The interactive lesson adds simulations, labs and quizzes for the same topic.

Answer the quiz questions for that area without looking at the notes, then check any you got wrong against the worked example. If a common mistake still tempts you, revisit that section.

Seeing where a formula is applied, such as in a car, a satellite or a power grid, makes it easier to remember and shows why the topic matters.

Physics content is checked carefully, but errors are possible. Check any important result against a textbook or your course notes, especially before an exam. The disclaimer page explains the limits of the material.