Mini-Lesson

Technical Understanding

This mini-lesson covers Technical Understanding for OCR A-level Product Design: forces and stresses, making structures stronger, material enhancement, and mechanisms and motion.

You will identify forces, stiffen structures, and calculate a mechanical advantage and a gear ratio. Press Start to begin.

Forces

Forces and stresses

Products must resist the forces acting on them. The five to recognise:

Tension — pulling apart (a cable).
Compression — crushing (a column).
Shear — forces sliding past each other (a rivet, scissors).
Bending — tension on one face, compression on the other (a beam).
Torsion — twisting (a drive shaft).

Stress = force ÷ cross-sectional area (N/mm² = MPa). Efficient shapes place material where stresses are greatest.

Quick check

Which force?

?A screwdriver shaft is turned hard against a stiff screw. Which force is applied along the shaft?

Structures

Making structures stronger and stiffer

Shape and construction add strength without much extra material:

Triangulation — triangles cannot be pushed out of shape, so they stiffen frames.
Webs and ribs — added walls resist bending and twisting.
I-beams and tubes — place material far from the neutral axis for high stiffness per mass.
Lamination — gluing thin layers (plywood, laminated beams) makes strong, stable members.

Quick check

Why triangulate?

?Why is a triangulated frame much stiffer than a rectangular one of the same members?

Enhancement

Enhancing material properties

Metals and timber can be treated to change their properties:

Annealing — heat then slow cool to soften and relieve stress.
Hardening — heat then quench high-carbon steel to make it hard but brittle.
Tempering — gently reheat hardened steel to restore toughness, trading a little hardness.
Work hardening — repeated deformation hardens but embrittles a metal.
Seasoning of timber and lamination also improve performance.

Calculate

Your turn — mechanical advantage

1A lever has an effort arm of 500 mm and a load arm of 100 mm. Mechanical advantage = effort arm ÷ load arm. Calculate the mechanical advantage.

Hint: 500 ÷ 100.

Mechanisms

Mechanisms and motion

Mechanisms control movement and force. Four types of motion: linear, rotary, reciprocating and oscillating.

Levers — change the size and direction of a force about a pivot.
Linkages — connect parts to change direction or type of motion.
Cams and followers — convert rotary motion into reciprocating motion.
Gears — change speed, torque and direction; gear ratio = driven teeth ÷ driver teeth.

Quick check

What a cam does

?A cam turning on a shaft lifts and lowers a follower. What does a cam-and-follower mechanism do?

Calculate

Your turn — gear ratio

2A gear train has a driver of 20 teeth and a driven gear of 60 teeth. Gear ratio = driven teeth ÷ driver teeth. Calculate the gear ratio (as a single number, ratio to 1).

: 1

Hint: 60 ÷ 20.

Sort it

Sort the technical terms

Tap a term, then the group it belongs to.

🧭 Type of force

🏗️ Structural technique

⚙️ Mechanism

Match it

Match each term to its meaning

Tap an item on the left, then its match on the right.

Term

Meaning

Recap

The big ideas to know

Forces: tension, compression, shear, bending, torsion; stress = force ÷ area

Structures: triangulation, webs/ribs, I-beams/tubes, lamination

Enhancement: annealing, hardening, tempering, work hardening, seasoning

Motion: linear, rotary, reciprocating, oscillating

Mechanisms: lever MA = effort arm ÷ load arm; gear ratio = driven ÷ driver teeth; cams give reciprocating motion

You have covered the forces, structures, treatments and mechanisms behind technical design.

🏆

Mini-lesson complete!

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You have worked through Technical Understanding for OCR A-level Product Design. 🎉

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