In a steam engine, what pushes the piston?
AnswerPressure of expanding steam
Heated water becomes high-pressure steam, which expands and drives the piston.
Science · Facts & stats
Engine facts & stats
7 fact-checked facts about engines, each with the reason behind it. 5 more are in today's round and join this page after it closes.
The basics
Which unit is traditionally used to describe an engine's power?
AnswerHorsepower
Horsepower was popularized in the 1700s to compare the output of steam engines with the work of horses.
Going deeper
How does a diesel engine ignite its fuel?
AnswerWith heat from strongly compressed air
Diesel engines squeeze air until it is hot enough that injected fuel ignites by itself, called compression ignition.
Which engine part turns the up-and-down motion of pistons into rotation?
AnswerCrankshaft
Connecting rods link the pistons to the crankshaft, which converts their back-and-forth motion into spinning.
A jet engine pushes an aircraft forward mainly by doing what?
AnswerBlasting a stream of hot gas out the back
Jet engines compress air, burn fuel in it and expel hot gas rearward; the reaction force drives the aircraft forward.
Expert level
Who built the first practical four-stroke gas engine, in 1876?
AnswerNikolaus Otto
Nikolaus Otto's 1876 engine made the four-stroke design practical, which is why it is called the Otto cycle.
In an engine, what does the compression ratio compare?
AnswerCylinder volume with the piston at the bottom vs at the top
Compression ratio is the cylinder's largest volume divided by its smallest volume as the piston travels up.
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