Topic 10: Mechanical Design (8 hours)

10.1 General concepts (4 hours)

	Assessment statement	Obj	Notes	References
10.1.1	Define mechanical advantage, velocity ratio and efficiency.	1	MA = load / effort VR = distance moved by effort / distance moved by load Efficiency = MA / VR	For Topic 10: www.technologystudent.com
10.1.2	Calculate mechanical advantage (MA), velocity ratio (VR) and efficiency for simple mechanical systems.	2
Levers
10.1.3	Describe first-, second- and third-class levers.	2	Identify load (L), effort (E) and fulcrum (F) in first‑class levers (E–F–L, for example, seesaw, crowbar, scissors), second-class levers (E–L–F, for example, wheelbarrow, bottle opener, nut cracker) and third‑class levers (L–E–F, for example, tweezers, broom, fishing rod).
10.1.4	Discuss the relevant efficiencies of the three classes of lever.	3
10.1.5	Explain that, when a lever is in equilibrium, the net moment is zero.	3
10.1.6	Calculate mechanical advantage and effort for first-, second- and third‑class levers.	2
Gears
10.1.7	Describe gear systems.	2
10.1.8	Calculate velocity ratio for gear systems.	2
10.1.9	Describe the function of different types of gears in a range of objects.	2	Use rack-and-pinion, bevel and worm gears.
10.1.10	Explain a design context in which a compound rather than a simple gear train would be appropriate.	3	Consider the gearing system on a metal lathe designed to be changed to cut a specific type of thread. Consider ratios, mechanical advantage and changes.
10.1.11	Discuss the function of different types of gears in a range of objects.	3	Use rack-and-pinion, bevel and worm gears.
Belts
10.1.12	Describe a belt or chain drive system.	2	Consider profile, load, changes in load, and speed.
10.1.13	Calculate velocity ratio for belt or chain drive systems.	2
10.1.14	Compare belt or chain drives and gear systems.	3	Consider profile, load, changes in load, and speed.
10.1.15	Design a system to provide belt torsion to a belt-and-pulley system.	3
Pulleys
10.1.16	Describe a pulley system.	2
10.1.17	Calculate mechanical advantage for pulley systems.	2
Inclined plane
10.1.18	Describe an inclined plane.	2	Consider inclined planes, screw threads and wedges.
10.1.19	Explain the advantage of an inclined plane.	3
10.2 Mechanical motion (2 hours)
10.2.1	Describe linear, rotary, intermittent, oscillating, reciprocating and irregular motion.	2
10.2.2	Explain how linkages can be used to change the direction of motion of components.	3
10.2.3	Discuss mechanical motion in a range of contexts.	3	Consider a hydraulic digger, a bicycle, a car jack and a hand drill.
10.2.4	Define torque.	1
10.2.5	Discuss the design features of a ratchet and pawl system.	3
10.2.6	Describe simple cam shapes and their advantages.	2
10.2.7	Identify cam followers and state their use.	2
10.2.8	Explain the use of a series of cam and follower mechanisms to achieve a set purpose.	3	This can be explored in a number of ways: using Lego, paper and pins, or through virtual online models.
10.3 Conversion of motion (2 hours)
10.3.1	Identify how mechanisms allow conversion of one form of motion to another.	2	For example, rack and pinion, bell cranks, toggle clamps, linkages and levers.
10.3.2	Identify the mechanisms in a bicycle.	2	Consider chain drive, levers, linkages and gears.
10.3.3	Design combinations of mechanisms to achieve specific tasks.	3	Consider the following tasks: · alter the axis of rotation · change the type of movement · increase force and decrease speed · decrease force and increase speed.
10.3.4	Discuss how designers make use of simple mechanisms in the home.	3	Consider water tap, garlic crusher and foot‑operated trash/rubbish bin.