Workshop Science: Basic Mechanics, Simple Machines and Fasteners
Basic mechanics, simple machines and fasteners
This domain tests levers, pulleys, inclined planes, screw jacks, mechanical advantage, velocity ratio, efficiency and the purpose of common fasteners. It connects force and distance in machines with practical assembly and lifting work.
Core rules
- Mechanical advantage MA = load/effort.
- Velocity ratio VR = distance moved by effort/distance moved by load.
- Efficiency = (MA/VR) × 100%; it is always below 100% in a real machine because of friction.
- For an ideal lever: load × load arm = effort × effort arm, with arms measured from the fulcrum.
- Pulley systems trade force for distance; a screw jack converts small torque into a large axial force.
- Fasteners include bolts and nuts, screws, rivets, keys, cotters and circlips. Threads may be right-hand or left-hand; preload and correct tightening matter.
Worked example
A lever has a load of 500 N at 0.3 m from the fulcrum and an effort arm of 1.2 m. Ideal effort = 500 × 0.3/1.2 = 125 N, so ideal MA = 500/125 = 4. With friction the actual effort is 150 N, giving actual MA = 500/150 = 3.33. Efficiency = 3.33/4 × 100 = 83.3%. The reasoning is to compare actual load/effort with the ideal lever ratio.
Traps
- Measuring lever arms from the end of the bar instead of the fulcrum.
- Treating MA and VR as the same quantity.
- Reporting efficiency above 100% for a real machine.
- Confusing a key with a cotter or a circlip with a rivet.
- Ignoring thread hand and preload when selecting fasteners.