Sources of energy and how they are generated, stored and converted, the principles of mechanical systems including the four types of motion, levers, linkages, cams, gears and pulleys, and the use of electronic systems and programmable components in products.

What this dot point is asking

AQA wants you to know how energy is generated, stored and converted, to explain the four types of motion and the common mechanisms that change motion or force (levers, linkages, cams, gears and pulleys), and to describe how electronic and programmable systems are used in products.

Energy sources and storage

Designers weigh availability, cost and environmental impact when choosing how to power a product. The choice of storage matters as much as the source: batteries store a large amount of energy compactly but degrade and contain problematic materials; capacitors release energy very quickly but hold little; springs and flywheels store mechanical energy directly, useful in wind-up products; and chemical fuels carry high energy density but burn. Designers also distinguish how energy is converted, since a product almost always changes one form into another (a motor turns electrical into kinetic energy, a heater into thermal, a speaker into sound), and each conversion wastes some energy as heat, which is why efficiency in use drives the life cycle impact of powered products.

Mechanical systems

The gear ratio is the central calculation and is defined as the number of teeth on the driven gear divided by the number on the driver: $\text{ratio} = \frac{\text{driven teeth}}{\text{driver teeth}}$. A ratio greater than one means the system gears down: the output turns slower than the input but with proportionally more torque, useful where a small motor must move a heavy load. A ratio less than one gears up: faster output, less torque. Output speed is the input speed divided by the ratio. Speed and torque trade off inversely because power (the product of the two) is conserved apart from friction losses, so you cannot gain both at once. The same principle applies to pulley systems through the ratio of pulley diameters, and to levers through the ratio of effort arm to load arm, where a longer effort arm multiplies force at the cost of distance moved. Mechanical advantage is the general term for this force-multiplying effect.

Mechanisms convert motion as well as multiply force. A cam and follower turns rotary input into reciprocating output, with the shape (profile) of the cam setting the pattern of the rise and fall. A crank and slider does the same in reverse in an engine, turning the reciprocating piston into rotary motion at the crankshaft. Linkages change the direction or magnitude of motion, for example a reverse-motion linkage that makes an output move opposite to an input. Knowing which mechanism produces which motion, and how the gear or lever ratio sets the speed and force, is the core of this part of the specification.

Electronic and programmable systems

Electronic systems follow an input, process, output model: a sensor input (light, temperature, movement) is sensed, the signal is processed (compared, counted, timed or computed), and an output device acts (a motor, light, buzzer or display). Naming all three parts is what AQA rewards, for example a security light whose input is a passive infra-red sensor, whose process is a controller deciding whether to switch on for a set time, and whose output is the lamp. Programmable components such as microcontrollers and PIC chips let one piece of hardware be reprogrammed for many different functions in software rather than rewired, making products flexible, smaller (fewer separate components) and smarter, and allowing the same board to be updated or repurposed. This is why so much modern functionality is "designed in software", which links electronics to digital design and to smart, responsive products.