The Push and Pull
Isaac Newton taught us that Force equals mass times acceleration ($F = ma$).
The SI Unit
- Newton (N): The force needed to accelerate 1 kilogram of mass at the rate of 1 meter per second squared.
The Imperial Chaos
- Pound-force (lbf): The force exerted by gravity on a mass of one pound on the surface of the Earth.
- Kilogram-force (kgf): Often called a kilopond. Similar to pounds-force, it's the gravitational force exerted by one kilogram of mass on Earth ($~9.806 N$).
The Microscopic
- Dyne: An old CGS (centimeter-gram-second) system unit. 100,000 dynes equal 1 Newton. It is still used to measure surface tension.