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QLDEngineering

Unit 4: Machines and mechanisms

10 dot points across 10 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do belt and chain drives transmit motion between shafts that are not touching?

Calculate the speed ratio of a belt or chain drive from the pulley or sprocket diameters, and compare belt and chain drives for slip, distance and load capacity
A QCE Engineering Unit 4 answer on belt and chain drives. Covers the speed ratio from pulley or sprocket sizes, direction of rotation, slip, and the trade-offs between flat belts, V-belts, toothed belts and chains, with worked drive arithmetic.
6 min answer →

How does a cam turn steady rotation into a controlled pattern of back-and-forth movement?

Explain how a cam and follower converts rotary motion into a programmed reciprocating or oscillating motion, and interpret the displacement diagram that describes the follower's movement
A QCE Engineering Unit 4 answer on cams and followers. Covers how a rotating cam drives a follower, the rise-dwell-fall pattern, types of cam and follower, the displacement diagram, and a worked reading of follower lift versus cam angle.
6 min answer →

How do engineers move from an ill-defined problem to a justified, tested machine solution?

Apply the engineering problem-solving process to a machine or mechanism brief, explaining how data, prototyping and evaluation against criteria drive the development of a justified solution
A QCE Engineering Unit 4 answer on the problem-solving process. Walks through exploring, developing, generating and evaluating phases, the role of design criteria and data, and how solutions are justified, with a worked example of comparing two mechanism options.
6 min answer →

How do gear trains change the speed and turning force transmitted through a machine?

Calculate the gear ratio, output speed and output torque of a simple and a compound gear train, and explain how gears trade rotational speed against torque
A QCE Engineering Unit 4 answer on gear trains. Covers gear ratio from tooth counts, the speed-torque trade-off, idler gears, compound trains and direction of rotation, with worked calculations of output speed and torque.
6 min answer →

How do levers and other simple machines multiply force, and what distinguishes the three classes of lever?

Analyse the three classes of lever using the principle of moments, and identify how simple machines such as levers, pulleys, wheel-and-axle and inclined planes provide mechanical advantage
A QCE Engineering Unit 4 answer on levers and simple machines. Covers the principle of moments applied to levers, the three classes of lever, and how levers, pulleys, the wheel-and-axle and inclined planes give mechanical advantage, with worked lever arithmetic.
6 min answer →

How do connected bars and pivots transmit and transform motion in a mechanism?

Explain how linkages and the four-bar mechanism transmit and change motion, identify common linkage types, and analyse the motion they produce from their geometry
A QCE Engineering Unit 4 answer on linkages. Covers the four-bar linkage, crank-rocker and crank-slider arrangements, reverse-motion and bell-crank linkages, and how the link lengths set the output motion, with a worked geometry calculation.
6 min answer →

How do engineers control a machine so it responds to its inputs and conditions?

Describe machine control using the input-process-output model, distinguish open-loop from closed-loop (feedback) control, and identify the role of sensors, controllers and actuators
A QCE Engineering Unit 4 answer on machine control. Covers the input-process-output model, open-loop versus closed-loop feedback control, the roles of sensors, controllers and actuators, and a worked example of a feedback control loop in a real machine.
6 min answer →

How do simple machines let a small input force move a large load, and at what cost?

Calculate mechanical advantage, velocity ratio and efficiency for simple machines such as levers, pulley systems and inclined planes, and explain the trade-off between force and distance
A QCE Engineering Unit 4 answer on simple machines. Defines mechanical advantage, velocity ratio and efficiency, explains the force-distance trade-off and friction losses, and works through a pulley and a lever with verified arithmetic.
6 min answer →

How are turning force, rotational speed and power related in a machine?

Calculate torque as the turning effect of a force, and relate torque and rotational speed to mechanical power transmitted by a rotating shaft
A QCE Engineering Unit 4 answer on torque and power. Covers torque as force times radius, the relationship between torque, angular speed and power, conversion of rev/min to rad/s, and how power is conserved through a drive, with worked arithmetic.
6 min answer →

What kinds of motion do machines produce and how do mechanisms convert one into another?

Classify the four types of motion (linear, rotary, reciprocating and oscillating) and explain how mechanisms convert between them in real machines
A QCE Engineering Unit 4 answer on types of motion. Covers linear, rotary, reciprocating and oscillating motion, the mechanisms that convert between them such as crank-sliders and cams, and a worked link between rotary speed and the linear speed it produces.
6 min answer →