Random notes on fractional horsepower and amperage

[Packard V8]

Having a garage sale today and had a bunch of bench grinders, air compressors and a fan lined up. When traffic was slow, I read motor data plates. For the dual voltage motors, below is the 115-volt:
1/4 horsepower - amps 3.5, 3.8, 4.2, 5.2
1/3 horsepower - amps 3.3, 4.3, 4.3
1/2 horsepower - amps 6.2
3/4 horsepower - amps 10.0
1 horsepower - amps 12.0, 13.0
1.5 horsepower - amps 17.9
Obviously, the motors are built to a purpose. Is it accurate to say the amps do the work and since there are big gaps between the fractions they choose the nearest?

jack vines

 

[tool_scrounge]

For AC motors, power = volts * current * power factor

power factor magnitude is 0 to 1.

I have seen tiny unloaded fractional horsepower motors use 10A. But they are cold to the touch. This is because the power factor is almost zero. So the real power used is also almost zero. So there is little heat.