25 January

Scale Drawing Practice for Vector Addition

Seng Kwang Tan IP3 01 Measurement, Simulations 0 Comments
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Bridging the Gap: A Digital Approach to Vector Scale Drawings

Vector addition is a fundamental concept in physics, yet students often struggle to visualize the connection between abstract numbers (magnitude, direction) and their geometric representation. I developed this Vector Scale Drawing App, a lightweight web-based tool designed to scaffold the learning process for vector addition, providing students with a “sandbox” to practice scale drawings with immediate feedback.

This Vector Scale Drawing App is not meant to replace pen and paper, but to complement it. A built-in guide walks novices through the process (Read -> Choose Scale -> Draw -> Measure).

“Pencil Mode”

The pencil mode allows students to make markings, trace angles, or draw reference lines without “committing” to a vector. Crucially, in Pencil Mode, the tools are “transparent” to clicks—you can draw right over the ruler, just like in real life.

This distinction helps students separate the *construction phase* from the *result phase*.

When students submit their answer (Magnitude and Direction), the app checks it against the calculated resultant. We allow for a small margin of error (5%), acknowledging that scale drawing is an estimation skill.

18 January

Base Unit Building Blocks

Seng Kwang Tan 01 Quantities and Measurement, IP3 01 Measurement 0 Comments

Base units are the fundamental building blocks from which all other units of measurement are constructed. In the International System of Units (SI), quantities such as length (metre), mass (kilogram), time (second), electric current (ampere), temperature (kelvin), amount of substance (mole), and luminous intensity (candela) are defined as base units because they cannot be broken down into simpler units. By combining these base units through multiplication, division, and powers, we can form derived units to describe more complex quantities—for example, speed (metres per second), force (newtons), and energy (joules).

This app teaches dimensional analysis by letting learners build derived physical quantities from the seven SI base units. Through an interactive fraction-style canvas, users place base-unit “bricks” into the numerator or denominator to form target dimensions (e.g., kg m⁻³ for density), reinforcing how exponents and unit positions encode physical meaning. Each quantity is accompanied by concise, inline hints that show the unit structure of the terms in its defining equation (for example, mass and volume in density, or force and area in pressure), helping students connect formulas to their base-unit foundations. By checking correctness and exploring more quantities (force, energy, power, electric charge, voltage, resistance, heat capacity, specific heat, latent heat, molar mass), learners develop an intuitive, transferable understanding of how physics equations translate into consistent SI units.

The app (https://physicstjc.github.io/sls/base-units/) can be directly embedded into SLS as the domain is now whitelisted.

06 December

Simulation for Series and Parallel Circuit

Seng Kwang Tan 16 Circuits, IP4 12 DC Circuits, Javascript 0 Comments
2.0 Ω
2.0 Ω
Drag the ammeter (A) or voltmeter (V) onto a bulb to attach. Ammeter measures current inline; voltmeter measures voltage across the bulb.
6V Battery Bulb 1 2Ω Bulb 2 2Ω A V

This interactive simulation helps students compare what happens in series and parallel circuits using two bulbs and a 6 V battery. Learners can switch between series and parallel configurations, adjust the resistance of each bulb, and see how this affects the current, voltage and brightness of the bulbs. By dragging the ammeter (A) into the circuit, they can measure the current through a chosen bulb, and by placing the voltmeter (V) across a bulb, they can measure the potential difference across it. The changing brightness of each bulb represents the power it dissipates, allowing students to visualise ideas such as: in a series circuit the current is the same through all components but the voltage is shared, while in a parallel circuit the voltage across each branch is the same but the currents can be different.

05 December

Simulation of electron drift speed versus temperature

Seng Kwang Tan 15 Currents, IP4 11 Current Electricity 0 Comments

Metal Lattice Simulation

3.0 V
20 °C
Mean drift speed: 0.0 mm/s
At low temperature, ions vibrate less, so collisions are fewer and drift speed (and current) is higher for 3.0 V.
Your browser does not support the HTML5 canvas tag.

This simulation demonstrates the principle that the resistance of a metal conductor increases with temperature. As temperature rises, the metal ions in the lattice vibrate more vigorously. This increased vibration causes charge carriers (electrons) to collide more frequently with the ions, hindering their movement. As a result, resistance increases and the current flowing through the conductor decreases for the same applied voltage.

At the A-Level, this simulation extends the understanding of current by examining it from a microscopic perspective in terms of mean drift velocity. Instead of viewing current simply as the rate of flow of charge, students learn that electrons in a conductor move slowly on average, with a small net drift in the direction of the electric field. The current depends on how many charge carriers are available and how fast they drift. This is expressed using the equation:

$$I = nAv_dq$$

where II is the current, nn is the number density of charge carriers, AA is the cross-sectional area of the conductor, vdv_dis the mean drift velocity of the electrons, and qq is the charge of each carrier. As temperature increases, more frequent collisions reduce the drift velocity, helping to explain why current decreases even though the charge carriers are still present—linking microscopic behaviour with macroscopic electrical measurements.

22 September

Misconception: Skydiver goes up when parachute opens

Seng Kwang Tan GeoGebra, IP3 03 Dynamics 0 Comments

When a parachute opens, many people think the parachutist suddenly shoots upward. This is not what really happens. The parachutist is always moving downward, but the parachute causes a very sharp deceleration. The large canopy produces a big upward drag force that slows the fall dramatically.

When people see videos of parachutists opening their parachutes, the camera angle can create a powerful illusion that the parachutist suddenly shoots upward. What really happens is that the parachutist decelerates sharply while the camera, usually attached to another skydiver, continues falling at almost the same high speed.

From the perspective of the camera, the parachutist with the open parachute is no longer keeping pace in the fall. The camera-holder is still dropping rapidly, but the parachutist has slowed down. In the video, this relative motion makes it look like the parachutist has bounced upward, when in fact they are still moving downward—just not as quickly.

The physics of air resistance shows clearly why the velocity cannot turn upward. Air resistance always acts opposite to the velocity and its size depends on speed. Before and after the parachute opens, the parachutist’s velocity is downward, so the drag force must be upward. If the parachutist’s velocity really were upward, then the drag would have to point downward. In that case, the resultant force would also point downward, making the acceleration greater than gravity—something we never observe. Instead, the drag force remains upward, which proves the parachutist is still moving downward the whole time. The chute simply reduces that downward speed to a safe value.

For a simulation on how the forces and velocity change with time, refer to this GeoGebra app.

19 September

Moving charge between two charged spheres

Seng Kwang Tan 14 Electric Fields 1 Comment

This simulation is made upon request by a colleague teaching JC2 this year.

The motion of a mobile charge between two source charges is governed by Coulomb’s law ($F = \dfrac{Q_1Q_2}{4\pi\epsilon_0r^2}$) and the electric field. Each source charge produces a field in space, exerting a force on the test charge according to $F = qE$. The total field is the vector sum of all source charges, with positive charges moving along the field and negative charges moving opposite to it.

The test charge’s acceleration depends on the net force, changing its velocity and trajectory according to Newton’s second law. Its motion shows how attractive and repulsive forces combine, providing an intuitive view of electrostatic interactions and field lines.

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