A four-bar linkage consists of:

Four gears arranged in a square that rotate simultaneously A chain with four links used to transmit force between two pulleys Four rigid links connected end-to-end by four pin joints, with one link fixed as the frame A four-legged support frame designed to resist lateral forces

The crank-slider mechanism is the basis of the piston internal combustion engine. What motion conversion does it perform?

Converts rotary motion of one shaft into rotary motion on a perpendicular shaft Converts oscillating motion into a perfectly circular rotation with constant speed Converts the linear (reciprocating) motion of the piston into the rotary motion of the crankshaft Converts electrical energy into mechanical rotary motion

A cam is an eccentric or specially shaped rotating disc that drives a follower. What is the main engineering advantage of a cam-and-follower system?

A cam can only produce simple harmonic (sinusoidal) motion in the follower Cams require no lubrication because the follower floats on a cushion of air The cam shape can be precisely designed to produce any required motion profile for the follower Cams convert rotary motion to rotary motion with a variable gear ratio

Ball bearings are preferred over plain (journal) bearings in high-speed electric motors because ball bearings:

Can carry higher axial (thrust) loads than any other bearing type Have much lower friction at high speed due to rolling contact rather than sliding contact Are self-lubricating and never require maintenance Are made from ceramics and therefore resistant to magnetic interference

A thrust bearing is specifically designed to carry:

Radial loads — forces perpendicular to the shaft axis Axial (thrust) loads — forces acting along the axis of the shaft Bending moments applied to the centre of the shaft Torsional (twisting) loads on a rotating shaft

An interference fit between a shaft and a hub means:

The shaft is smaller than the hole, allowing free rotation with minimal friction The shaft and hole are exactly the same size to within 0.001 mm The shaft is slightly larger than the hole, so the parts must be pressed together and grip each other firmly without a fastener The shaft expands when heated and contracts when cooled to create a timed release

In a clearance fit, the shaft is always smaller than the hole. This type of fit is used when:

The parts must be permanently locked together without screws The parts need to slide or rotate relative to each other, such as a journal bearing The parts need to be precisely aligned but stationary The hole is used in tension and must not expand under load

Hydrodynamic lubrication in a journal bearing works by:

Oil is pumped in at high pressure to push the shaft away from the bearing The rotating shaft dragging oil into a converging wedge-shaped gap, generating pressure that lifts the shaft clear of the bearing surface PTFE particles in the oil crystallise on the surface to form a solid film Magnetic fields in the bearing repel the shaft to prevent contact

Why are tolerances on mating engineering parts specified in manufacturing drawings?

To specify the surface finish so the part looks attractive To define the acceptable range of dimensions so parts made on different machines will fit together and function correctly To indicate the maximum weight the part can support To specify the material hardness required for the manufacturing process

Grease lubrication is preferred over oil lubrication for slow-speed, sealed bearings (such as wheel hub bearings on a bicycle) because:

Grease has lower viscosity than oil, reducing friction at high speed Grease conducts heat better than oil, cooling the bearing more effectively Grease stays in place without a sealed reservoir and provides adequate lubrication with minimal maintenance Grease prevents corrosion by reacting chemically with the bearing steel

A Scotch-yoke mechanism converts rotary motion of a crank pin into:

Uniform linear velocity with sudden direction reversals Pure simple harmonic (sinusoidal) linear motion of the yoke Rotation about a second axis perpendicular to the first Variable-ratio rotation similar to a non-circular gear

Roller bearings are chosen over ball bearings for the wheel axles of heavy freight wagons because roller bearings:

Spin faster than ball bearings, reducing journey time Are made from polymer rather than steel, which is lighter Have larger contact areas between rolling elements and races, allowing them to carry heavier radial loads Are self-aligning, compensating for any misalignment between the axle and the wagon frame