Technological World: mechanisms, electricity, and systems analysis
This domain examines simple machines, mechanical advantage, electrical circuits, and how systems transform inputs into outputs. Expect calculations with levers, gears, Ohm's law, series and parallel circuits, and efficiency.
Mechanisms
A lever has an effort, a load, and a fulcrum. Mechanical advantage (MA) compares load force to effort force: MA = load / effort. For gears, the speed ratio depends on tooth counts: a driven gear with more teeth turns more slowly and with more torque. Pulleys can change force direction and, in movable arrangements, multiply force. No machine is perfectly efficient; friction converts some useful energy into thermal energy.
Electricity
Current (I) is charge flow in amperes; voltage (V) is energy per charge in volts; resistance (R) is opposition in ohms. Ohm's law: V = IR. In a series circuit, current is the same through components and voltages add. In a parallel circuit, voltage is the same across branches and currents add. Electrical power is P = VI, and energy is power × time.
Systems analysis
A system has an input, a process, an output, and often feedback. An open-loop system does not use feedback to adjust itself; a closed-loop system measures output and corrects the process. Efficiency = useful output energy / input energy × 100%. Losses are usually heat, sound, or friction.
Worked example
A 12 V source is connected across a 4 Ω resistor. Using V = IR: I = V/R = 12 V / 4 Ω = 3 A. Power = VI = 12 V × 3 A = 36 W. If the resistor were replaced by two 4 Ω resistors in series, total resistance would be 8 Ω, so current would fall to 1.5 A. The reasoning shows that increasing resistance in a fixed-voltage circuit decreases current.
Traps
- Confusing mechanical advantage with speed ratio.
- Saying current is used up in a series circuit.
- Adding voltages across parallel branches instead of keeping them equal.
- Mixing units: volts, amperes, ohms, watts.
- Reporting efficiency above 100% by counting input and output incorrectly.
- Treating feedback as present in every system.