Physics Study Guide: Units, Sketches, Formulas and Calculation Steps

Every physics formula rests on the seven base quantities of the International System: length in metres, mass in kilograms, time in seconds, electric current in amperes, temperature in kelvin, amount of substance in moles, and luminous intensity in candelas. Everything else, from velocity and force to energy and pressure, is a derived quantity whose unit is assembled from those seven. A newton, for instance, equals a kilogram metre per second squared, and a joule equals a kilogram metre squared per second squared.

The most common beginner mistake comes from mixed units. Drop 72 km/h straight into a formula alongside an acceleration in metres per second squared and the result looks tidy while being wrong by a large factor. The fix is simple: divide by 3.6, so 72 km/h becomes 20 m/s. A mass of 250 grams becomes 0.25 kilograms, and 15 centimetres becomes 0.15 metres. The prefixes are worth knowing cold as well: milli is ten to the minus three, micro ten to the minus six, kilo ten to the three, and mega ten to the six.

Good practice for this part deliberately strips away the story of a problem. Write down twenty random values with mixed units, convert every one to SI, and express each in scientific notation. It feels trivial, yet it frees attention when a real problem arrives, because the conversion happens automatically and the learner can think about the physics instead.

Kinematics is the most concrete opening chapter because the motion can be seen. Motion at constant velocity gives a straight sloping line on a position-time graph and a flat line on a velocity-time graph. Motion with constant acceleration gives a sloping line on the velocity-time graph and a curve shaped like a parabola on the position-time graph.

Two ways of reading these graphs need to become second nature. The gradient of a position-time graph is velocity, and the gradient of a velocity-time graph is acceleration. The area under a velocity-time graph is displacement. From those three facts a learner can derive the constant-acceleration equations unaided: v = u + a t comes from the gradient, s = u t + one half a t squared comes from the area of a trapezium, and v squared = u squared + 2 a s follows from combining the two.

A worked case shows the payoff. A car travelling at 20 m/s brakes with a deceleration of 4 m/s squared. Its velocity line falls straight from 20 to zero in 5 seconds, and the area of the triangle beneath, half of 5 times 20, gives a stopping distance of 50 metres. A learner who sketches the graph first reaches the same number without having to remember which equation to pick.

Many learners arrive at physics with ideas about motion built from everyday experience. Two are especially common: heavy objects fall faster than light ones, and a moving object must be pushed by some force to keep going. Both feel reasonable, and both sit far closer to Aristotle than to Newton. The Force Concept Inventory, developed by Hestenes and colleagues, was designed precisely to surface beliefs of this kind.

Intuitive ideas are stubborn, and the way to shift them is to test them repeatedly. Write down a prediction before working a problem or running an experiment, then compare it with what happens. The free PhET interactive simulations from the University of Colorado Boulder help here: drop two objects of different mass with air resistance switched off, or push a box across a frictionless surface and let go, and watch closely. A box released from the push keeps moving at constant velocity for as long as no force acts to stop it.

Richard Hake's survey of 6,542 students in introductory physics courses found that teaching methods which make learners think actively, discuss and explain produced roughly double the gain in conceptual understanding compared with listening to explanations alone. In practice that makes explaining a concept in one's own words, to a study partner or out loud to oneself, a core exercise in mechanics.

Once dynamics feels comfortable, the chapters on work, energy and momentum offer a second way into motion problems. The force approach tracks what happens at every instant, whereas the conservation approach simply compares the starting state with the final one. In a system without friction, kinetic plus potential energy stays constant. A ball released from 5 metres, taking g as 10 m/s squared, reaches the ground at the square root of 2 times 10 times 5, which is 10 m/s, and its mass plays no part at all.

Momentum, mass times velocity, is conserved in collisions and explosions as long as no external force acts on the system. Problems about two trolleys that collide and stick together, or a bullet fired from a rifle, shrink to a few lines once the learner writes total momentum before equal to total momentum after. Kinetic energy in a sticking collision actually decreases, and noticing that difference is a sign of real maturity in the topic.

A useful habit is to look for what stays constant before choosing an equation. With no friction and a question about speed at another point, energy is usually the fastest route. With a collision, momentum. A good comparison exercise is to solve one smooth-slope problem twice, once with Newton's laws and the constant-acceleration equations and once with energy conservation, and confirm that both give the same answer.

Under Indonesia's Kurikulum Merdeka, Grade 10 physics still sits inside general science alongside biology and chemistry, focusing on measurement, quantities, straight-line motion and energy. Physics becomes its own subject from Grade 11, with dynamics, work and energy, momentum, oscillations, waves and fluids. Grade 12 brings electricity, magnetism and an introduction to modern physics. These topics feel more abstract because the things being discussed, such as current or a field, cannot be seen directly.

The same working method still applies. A circuit is drawn before it is calculated, with the direction of current marked. Ohm's law, V = I R, reads as a proportion: for a fixed resistance, doubling the voltage doubles the current. Resistances in series add directly, while resistances in parallel add as reciprocals. For waves, speed equals wavelength times frequency, so on the same medium a rising frequency means a shorter wavelength. In modern physics, the energy of a photon is proportional to its frequency.

Learners who are fluent in mechanics usually find that electricity and waves call on the same tools: unit analysis, proportional reasoning and tidy bookkeeping of steps. For students at international schools, the equivalent material appears in IGCSE Physics, AS and A Level Physics or IB Physics, and it helps to pair the English terms with their Indonesian counterparts early on when switching between the two.