Track wave energy without carrying the medium along
Follow a disturbance and a marked part of its medium as two different motions.
Exam scope and assessment notes
Mapped to the named 0973 section using teaching from the corresponding single-science course. A 0973-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade. This qualification reports two grades on the 9–1 scale; confirm the entry route for your zone and exam series.
Before you begin
- Distinguish an object's motion from a changing pattern.
- Recognise energy transfer between locations.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
A marker rises and falls at the same horizontal location while a pulse moves right. Which motion is local?
What you will learn
- Know that waves transfer energy without transferring matter along with the wave.
- Distinguish local oscillation from the travelling pattern.
The disturbance travels while a marker stays local
A pulse moving along an ideal stretched rope passes successive parts of the rope. A marked part rises and falls near its original position while the disturbance travels along the rope. Energy can reach a distant part, even though the same piece of rope has not travelled there. Use that difference to explain wave transfer, rather than treating the moving shape as a transported lump of rope.
In a simple wave model, each part of a material medium oscillates locally. The wave propagates through successive interactions. Electromagnetic waves also transfer energy and do not require a material medium at all. The general energy-transfer statement is not a requirement that every kind of wave must have rope-like particles.
Interpret the observations within their conditions
The supplied snapshots label the same rope marker at one horizontal position while the pulse changes position. The marker's displacement changes; its identity and local reference position remain the same. Its vibration speed is not the pulse's propagation speed. The drawing is a qualitative teaching model, not measured motion or a model of every real water surface.
Currents, large-amplitude effects or other imposed motion can transport material in real situations. That does not justify identifying ordinary wave propagation with bulk transport of the medium in this school model. A floating object that drifts because of a separate current needs a separate account; a wave crest alone is not a tagged parcel of water.
Sources for this lesson
Pause and explain
Which statement expresses the selected wave-transfer model?
Worked example
A rope pulse moves 1.2 m right while a marked point moves up and down near its original horizontal location. What moves along the rope?
Show the worked solution
- The travelling disturbance changes horizontal position.
- The marked material point oscillates locally.
- Energy travels with the disturbance, rather than the marked rope point travelling 1.2 m.
Answer The disturbance and energy propagate; the marked medium oscillates locally.
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Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain the difference between a rope pulse travelling right and a marked rope point rising and falling.
Give me a hint
Name the pattern and material motions separately.
Compare my reasoning
- The pulse changes position along the rope.
- The marked point oscillates near its reference location.
- Energy can propagate without that point moving along the whole path.
Travelling disturbance; local medium oscillation.
Look for these in your work
- Identify both motions.
- Link propagation to energy transfer.
A disturbance passes markers A, B and C in order. Does this show that marker A became marker C?
Give me a hint
Keep the identity of each material point separate from the pattern.
Compare my reasoning
- A, B and C are different parts of the medium.
- Each responds locally as the disturbance arrives.
- Sequential response is not transport of A into C.
No; successive material points respond to a travelling disturbance.
Look for these in your work
- Retain each marker's identity.
- Avoid treating the wave as a parcel.
A float drifts in a water current while ripples pass. Can all its drift be attributed to the ideal wave model?
Give me a hint
There is also a stated bulk flow.
Compare my reasoning
- The current can transport water and a float.
- Ripples are a travelling wave pattern.
- Separate current-driven drift from the local-oscillation account.
No; the imposed current needs a separate material-transport account.
Look for these in your work
- Identify the additional process.
- Keep the model's scope explicit.
Common mistakes
- A crest is a feature, not a tagged material parcel.
- Particle vibration speed is not wave speed.
- Separate an imposed current from the school wave model.
What can you explain now?
Does a pulse reaching the other end require the same rope particle to arrive there?
Compare with the explanation
No.
Successive local interactions transfer the disturbance and energy.
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Make it stick
Explain wave propagation with a local marker and distinguish energy transfer from bulk material transport.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.