Legacy Systems & Control: structures and mechanisms
Study the older option's structural members, equilibrium, stress/strain, mechanical advantage, gear ratios and motion conversion.
Section 27-4.3-TERMS · 2024–2027 · Systems & Control mechanisms · mechanical terms
Exam scope and assessment notes
StudyForA provides original teaching and scenario-based practice, not Cambridge past papers, official marks or an authenticated practical course. It cannot assess a candidate's actual workshop skills, finished product or Component 2 portfolio. Component 2 is school-based, internally assessed and externally moderated; the teacher authenticates candidate work. Any real making requires centre facilities, risk controls and direct qualified supervision. Candidate project work must remain their own. Follow the syllabus for the exam year.
Before you begin
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
A 24-tooth gear drives a 12-tooth gear. In an ideal external gear pair, how does the driven gear speed compare?
What you will learn
- Identify beams, struts and ties; explain loads, joints, reinforcement and factor of safety.
- Use simple force, stress/strain and mechanism relationships in exam-style design contexts.
From structural form to safe loading
The 2024–2027 Systems & Control option develops the common structure material into beams, struts and ties; applied loads and reactions; joints and reinforcement; and how length, cross-section and material affect performance. It introduces equilibrium, stress as force per cross-sectional area, strain as extension per original length, and factor of safety.
Stress and strain calculations depend on consistent units and a clear definition of the loaded area and original length. A factor of safety expresses a margin between a design load and a failure limit; it does not make an untested structure safe. Real load-bearing products require qualified engineering review.
Choose mechanisms and calculate trade-offs
Older Systems & Control candidates study load, effort, fulcrum, mechanical advantage, velocity ratio and efficiency. Mechanisms include levers, gear trains, belts/pulleys, chains, bearings and motion converters such as cranks, cams, ratchets and screw threads.
For an ideal simple machine, mechanical advantage compares output load with input effort; velocity ratio compares input distance or speed with output distance or speed; efficiency compares useful output with input. A larger force advantage usually involves greater input movement or lower output speed. Use diagrams and units to avoid mixing ratios.
Sources for this lesson
Pause and explain
How is stress calculated in the simplified syllabus relationship?
Worked example
A lever balances a 120 N load 0.20 m from a fulcrum. The effort acts 0.60 m away. Find the ideal effort and explain one real-world limitation.
Show the worked solution
- For equilibrium, load × load arm = effort × effort arm.
- Effort = (120 × 0.20) ÷ 0.60.
- Effort = 40 N in the ideal model.
- Actual effort may be higher because of friction, deformation and mechanism mass.
Answer The ideal effort is 40 N. The model assumes equilibrium and ignores losses; real friction at the pivot and material deformation may require more force. Check units and do not use a classroom calculation to approve real lifting equipment.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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.
A beam carries a load and is supported at two points. What should be drawn or calculated before choosing a reinforcement?
Give me a hint
Show loads, supports, reactions, member geometry and material.
Compare my reasoning
- Draw the beam, load location and supports.
- Check force balance and identify the member's bending response.
- Compare the section or reinforcement and consider the joints.
Draw the load and reactions, check equilibrium, and identify likely bending and joint stresses. Then compare section geometry or reinforcement with a test model. A real beam cannot be approved by this school-level analysis alone.
Look for these in your work
- Represents load conditions
- Uses equilibrium reasoning
- Includes connection details
A gear train must reduce speed to one third. What tooth-count relationship could achieve that in one ideal pair, and what else should be checked?
Give me a hint
For a driven gear slower than its driver, use a larger driven gear.
Compare my reasoning
- Write driven speed ÷ driver speed as the desired ratio.
- Relate speed ratio to driver and driven tooth counts.
- Check direction, torque, size, load and friction.
A driven gear with three times the driver's tooth count gives an ideal output speed of one third and turns in the opposite direction. Check that the larger gear fits, that the teeth and shafts can carry the load, and account for losses and guarding.
Look for these in your work
- Uses tooth-count relationship
- States rotation direction
- Checks physical constraints
A small model bridge has stress = 2 N/mm² under a test load. Can this value certify a full-size bridge? Explain what is missing.
Give me a hint
Scale, material, joints, dynamic loads, safety factors and professional design are not established.
Compare my reasoning
- State what the model calculation describes.
- List factors that change with scale and full-size use.
- Identify qualified review and standards required for real structures.
No. It describes only the model and stated loading assumptions. Full-size material properties, joints, geometry, dynamic loads, environmental conditions, safety factors, codes and manufacturing quality are missing. Real bridges need qualified engineers and formal review.
Look for these in your work
- Limits the calculation claim
- Names relevant missing factors
- Recognises professional review
Common mistakes
- Using the wrong lever arm or mixing cm and m
- Reporting an ideal mechanical advantage as actual efficiency
- Treating factor of safety as proof that an untested structure is safe
What can you explain now?
How is stress calculated in the simplified syllabus relationship?
Compare with the explanation
Stress = force ÷ cross-sectional area.
The result depends on the force direction and consistent area units.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Recall the main decision in “Legacy Systems & Control: structures and mechanisms”, name the evidence that supports it, and identify one limitation that still needs checking.
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.