Choose mechanisms to change motion or force
Identify common motion types and compare levers, gears, belts, pulleys, chains and linkages for product needs.
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
Which mechanism can transfer rotation between separated shafts using a flexible loop?
What you will learn
- Identify rotary, linear, reciprocating and oscillating motion and simple motion conversion.
- Compare common mechanism types, force/direction effects and friction reduction in context.
Describe movement before selecting a mechanism
Rotary motion turns around an axis; linear motion travels along a line; reciprocating motion repeats back-and-forth travel; oscillating motion swings through an angle. A mechanism can transfer motion or convert it from one type to another.
First-, second- and third-class levers place the fulcrum, load and effort in different orders. Gears, pulleys and belts, and sprockets with chains can transfer rotary motion, alter direction, speed or force, depending on arrangement and size.
Account for friction and use
Moving surfaces lose energy through friction. Design can reduce unwanted friction by choosing suitable contact, alignment and bearings; lubrication can also help where appropriate. The lubricant must suit materials, temperature and use.
Choose a mechanism from the task: required movement, available space, load, speed, noise, maintenance and safety. A mechanism that multiplies force may reduce output speed or require greater input travel; state the trade-off rather than saying it is simply 'better'.
Sources for this lesson
Pause and explain
What motion does a crank-slider commonly convert?
Worked example
A hand-operated display needs a slow, controlled rotation from a fast-turning input. What mechanism features should be compared?
Show the worked solution
- Set the required output motion, direction and approximate speed.
- Compare gear or belt ratios and the available space.
- Check friction, alignment, guarding and maintenance needs.
- Model or calculate the proposed ratio before selecting.
Answer A gear train or pulley arrangement could reduce output speed depending on relative sizes. Check the ratio, direction, available space, friction and safe guarding. A physical model can verify the motion; the selected arrangement depends on the required load and smoothness.
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 toy window wiper must move back and forth from a rotating motor. Which mechanism could help, and what should be checked?
Give me a hint
Look for rotary-to-reciprocating conversion and safe link geometry.
Compare my reasoning
- Identify input and output motions.
- Choose a crank and linkage or another suitable converter.
- Check stroke, clearance, friction and pinch risks in a model.
A crank-slider or linkage can convert rotation into back-and-forth motion. Check the required stroke, clearances, joint friction and pinch points using a small model, then guard moving parts in any real product.
Look for these in your work
- Identifies motion conversion
- Checks output travel
- Considers safety
A hand winch needs the user to turn a drum slowly while lifting a load. Why might gears be useful, and what trade-off should be explained?
Give me a hint
Compare input effort and output speed; include load and efficiency.
Compare my reasoning
- Describe input and output motion.
- Select a plausible gear reduction and identify the direction change if relevant.
- Explain force/speed and friction trade-offs.
A reduction gear can make the drum turn more slowly while increasing available output torque for a given input, subject to losses. The user may need more turns, and gear friction, strength and safe load limits matter. A real lifting mechanism must be engineered and tested professionally.
Look for these in your work
- Explains the function of gearing
- States the travel/speed trade-off
- Recognises load safety
A paper-cutter linkage has become stiff after dust entered its pivot. What should a designer investigate before adding lubricant?
Give me a hint
Check materials, contamination source, alignment and the suitable maintenance method.
Compare my reasoning
- Identify the pivot materials and product environment.
- Inspect alignment, wear and the source of dust.
- Choose a compatible maintenance or design change under safe conditions.
First identify the materials, dust source and whether the pivot is worn or misaligned. The correct lubricant may depend on material and use; a dry bushing, shield or cleaning schedule could be more suitable. A teacher should supervise workshop maintenance.
Look for these in your work
- Investigates root cause
- Checks material compatibility
- Considers design as well as lubricant
Common mistakes
- Confusing linear and reciprocating motion
- Claiming a mechanism increases force and speed at the same time without a source of energy
- Ignoring friction, alignment and guarding
What can you explain now?
What motion does a crank-slider commonly convert?
Compare with the explanation
Rotary motion to reciprocating linear motion, or the reverse.
The crank turns while the connecting slider moves repeatedly along a line.
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 “Choose mechanisms to change motion or force”, 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.