For IB Diploma students and parents, the useful question is often: which decision went wrong? At Baccalaureate Classes, online IB Physics tutoring helps students connect physical understanding with independent problem-solving.
Find the difficulty before adding more practice
| If the student struggles with | Start by checking |
|---|---|
| Choosing an equation | The physical model and its assumptions |
| Explaining an answer | The link between cause and consequence |
| Reading a graph | Axes, slope and the relationship being tested |
| A changed question | Whether the method was understood or remembered |
1. A lift moving upwards but slowing down
Question: A student stands on a scale in the lift. Is the reading greater than, equal to or less than their weight?
| First impression | Physical reasoning |
|---|---|
| Moving upwards means a larger reading | Slowing while moving upwards means downward acceleration |
| The scale measures weight directly | The scale measures the upward normal force N |
Taking upwards as positive gives:
N − mg = ma
Here a is negative, so N < mg. The scale reading is smaller than the student's weight, assuming the student remains in contact with it.
Try a change: The lift moves downwards and slows. Acceleration is now upwards, so N > mg. Ask the student to explain the direction before calculating.
2. Trolleys that stick together after a collision
A 2 kg trolley travelling at 3 m/s hits a stationary 1 kg trolley. They stick together. Assume negligible external impulse on the two-trolley system during the collision.
| Quantity | Before collision | After collision |
|---|---|---|
| Momentum | 2 × 3 = 6 kg m/s | 3v = 6, so v = 2 m/s |
| Kinetic energy | ½ × 2 × 3² = 9 J | ½ × 3 × 2² = 6 J |
The common velocity is 2 m/s in the original direction. Momentum is conserved under the stated assumption. Kinetic energy decreases by 3 J, transferred to other forms such as internal energy and sound.
The key decision: Sticking together identifies a perfectly inelastic collision. Do not assume that kinetic energy is conserved simply because the problem involves a collision.
Check understanding: Which objects form the system? Why can momentum conservation be used? Where does the kinetic energy go?
3. Light entering glass
Light crosses a stationary boundary from air into stationary glass. Its speed decreases. Which changes: frequency, wavelength or both?
| Quantity | What happens | Reason |
|---|---|---|
| Frequency f | Unchanged | The frequency is continuous across this stationary boundary |
| Speed v | Decreases | Light travels more slowly in glass |
| Wavelength λ | Decreases | With f unchanged, λ = v/f |
Example: f = 5.0 × 10¹⁴ Hz and v = 2.0 × 10⁸ m/s in glass.
λ = v/f = 4.0 × 10⁻⁷ m = 400 nm
The key decision: Identify what stays constant before substituting numbers. The equation v = fλ alone does not explain which variable changes.
Try a change: If the speed halves at another stationary boundary, the wavelength halves while frequency remains unchanged.
4. Cooling water and the meaning of rate
Two identical cups hold equal masses of water at different temperatures in the same room. Which initially cools faster?
Under comparable heat-transfer conditions, the hotter water generally has a greater initial cooling rate because its temperature difference from the room is larger.
| What the equation tells you | What it does not tell you alone |
|---|---|
| Q = mcΔT relates energy transfer to temperature change | How quickly that energy transfer happens |
| A temperature change can be used to calculate energy transferred | The temperature change per second throughout cooling |
Sketch check: On a temperature–time graph, cooling rate is linked to the magnitude of the gradient. A typical cooling curve becomes less steep as the water approaches room temperature.
Ask the student: Why should the curve flatten? Their explanation should connect the changing temperature difference with the changing rate, under the model being used.
5. A curved electrical graph
A student plots potential difference V vertically against current I horizontally. The curve becomes steeper as current increases. Can one gradient be called the resistance?
| Graph or calculation | Interpretation |
|---|---|
| V/I at an operating point | Resistance at that point |
| Gradient of a tangent | Local rate of change dV/dI; may differ from V/I |
| Straight V–I line through the origin | Supports constant resistance over that range |
| Curved V–I relationship | Requires interpretation of the component and conditions |
For an ohmic conductor at constant temperature, the straight-line gradient equals resistance. A filament lamp can behave differently as its temperature changes.
The key decision: Units alone do not establish meaning. Both V/I and the tangent gradient have units of ohms, yet they can represent different quantities for a nonlinear component.
A short routine for unfamiliar Physics questions
- Describe the situation in words before selecting an equation.
- Draw the system, forces, boundary or relevant graph.
- State the assumption that makes the method appropriate.
- Calculate and check units, direction and plausibility.
- Change one feature and explain what happens next.
Use the final step after closing the worked solution. Reversing the lift's acceleration or changing the graph axes tests whether the student can transfer the reasoning.
What students and parents can look for
| Useful sign of progress | A practical check |
|---|---|
| More independent starts | Can the student identify the governing principle? |
| Clearer explanations | Can they connect a cause with its physical consequence? |
| Better use of feedback | Can they correct the particular reasoning error? |
| Understanding that lasts | Can they solve a changed example several days later? |
Keep feedback specific. "Careless mistake" gives little direction. "Assumed upward motion meant upward acceleration" identifies exactly what needs attention.
Discuss a specific Physics difficulty with us
For a focused discussion with Baccalaureate Classes, share a recent question, the student's attempt and teacher feedback. Include the HL or SL level, examination session and upcoming deadline.
These details help distinguish missing knowledge from difficulty choosing a model or explaining a result. Our online IB Physics tutoring supports conceptual understanding, numerical problem-solving and assessment preparation.
Explore online IB Physics tutoring for HL and SL
The IB describes Physics as an experimental subject involving mathematical models, evidence and scientific limitations. [1] The examples here turn that emphasis into practical learning checks. They are teaching illustrations, not predicted examination questions.