kg·m/s to lb·ft/s Converter
Convert kilogram-meters per second to pound-feet per second by multiplying by 7.233014. Includes the formula, a conversion table, and why momentum shares its unit with impulse.
kg·m/s to lb·ft/s
Formula
Multiply by 7.233014.
The factor is just the mass and length factors multiplied together: 2.204623 lb per kg × 3.280840 ft per m = 7.233014. Momentum is mass times velocity, so its conversion factor is the product of the factors for each part.
Worked example
A 1,500 kg car at 20 m/s has momentum:
In imperial units:
Conversion table
| kg·m/s | lb·ft/s |
|---|---|
| 1 | 7.233014 |
| 2 | 14.46603 |
| 3 | 21.69904 |
| 5 | 36.16507 |
| 10 | 72.33014 |
| 20 | 144.6603 |
| 50 | 361.6507 |
| 100 | 723.3014 |
| 250 | 1,808.253 |
| 500 | 3,616.507 |
| 1,000 | 7,233.014 |
Momentum and impulse share a unit
One kg·m/s is also exactly one newton-second (N·s), and that is not a coincidence. A newton is kg·m/s², so a newton-second is kg·m/s — the same thing written from the other direction.
The physics behind it is the impulse–momentum theorem: a force applied for a time changes momentum by exactly that force times that time.
This is why airbags work. The change in momentum in a crash is fixed by the car's mass and speed. Stretching the stopping time from 20 ms to 200 ms divides the force on the occupant by ten.
It is also why rocket engines are rated in newton-seconds of total impulse, and why model rocket motors carry class letters that each double the impulse of the last.
Reference momenta
- Tennis ball served at 50 m/s — 2.9 kg·m/s = 21 lb·ft/s
- Football kicked at 30 m/s — 13 kg·m/s = 94 lb·ft/s
- Sprinter at full speed — 800 kg·m/s = 5,786 lb·ft/s
- Car at 20 m/s — 30,000 kg·m/s = 216,990 lb·ft/s
- Lorry at 25 m/s — 1,000,000 kg·m/s = 7.23 million lb·ft/s
FAQ
How many lb·ft/s is 1 kg·m/s? 7.233014 lb·ft/s.
How many kg·m/s is 1 lb·ft/s? 0.1382550 kg·m/s.
Is a newton-second the same as a kg·m/s? Yes, exactly. They are the same unit under two names — one emphasises impulse, the other momentum.
Where does 7.233014 come from? It is 2.204623 × 3.280840 — the kilogram-to-pound factor times the metre-to-foot factor.
Is momentum conserved? Yes, in any closed system with no external force. That is what makes it more useful than velocity alone when analysing collisions.