spur gear

spiral gear

bevel gear

worm gear

maximum and zero

zero and maximum

minimum and maximum

zero and minimum

base circle

pitch circle

root circle

prime circle

double helical gears having opposite teeth

double helical gears having identical teeth

single helical gear in which one of the teeth of helix angle a is more

mutter gears

Machines transmit mechanical work, whereas structures transmit forces

In machines, relative motion exists between its members, whereas same does hot exist in case of structures

Machines modify movement and work, whereas structures modify forces

Efficiency of machines as well as structures is below 100%