Physics
What the module tests
Physics covers matter, mechanics, statics, kinetics, fluid dynamics, thermodynamics, light and sound. The exam favours applied mechanics: mass versus weight, moments, pressure, density, energy, and the gas laws in a maintenance context.
Core rules
- Weight = mass × gravitational acceleration; on Earth use about 9.81 m/s².
- For a body in equilibrium, clockwise moments equal anticlockwise moments about the same pivot.
- Pressure = force/area; 1 bar = 100 kPa; gauge pressure = absolute pressure minus atmospheric pressure.
- Density = mass/volume; relative density compares a substance with water.
- In a hydraulic system, pressure is transmitted equally (Pascal's principle), so force depends on piston area.
Worked example
A 12 kg component hangs 0.8 m from a pivot. What mass at 1.2 m on the other side balances it? Weight = 12 × 9.81 = 117.7 N. Moment = 117.7 × 0.8 = 94.2 N·m. Required force at 1.2 m = 94.2/1.2 = 78.5 N. Mass = 78.5/9.81 = 8.0 kg. The ratio of distances is 1.2/0.8 = 1.5, so the mass must be 12/1.5 = 8 kg.
Traps
Using mass instead of weight in moment calculations; mixing gauge and absolute pressure; forgetting that pressure acts normal to a surface; using the wrong area in hydraulic calculations; ignoring that a larger piston gives more force but less travel.
Exam approach
Draw a simple free-body sketch, mark distances from the stated pivot, and keep units consistent. If two answers differ only by the factor 9.81, you have probably confused mass with weight.