Calories (th)/second to Foot pounds-force second
cal(th)/s
ft·lbf/s
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
1 cal(th)/s (Calories (th)/second) → 3.08596003256770319158 ft·lbf/s (Foot pounds-force second) Just now |
Quick Reference Table (Calories (th)/second to Foot pounds-force second)
| Calories (th)/second (cal(th)/s) | Foot pounds-force second (ft·lbf/s) |
|---|---|
| 0.1 | 0.30859600325677031916 |
| 1 | 3.08596003256770319158 |
| 10 | 30.85960032567703191585 |
| 14.3 | 44.12922846571815563966 |
| 100 | 308.59600325677031915845 |
| 1,000 | 3,085.96003256770319158455 |
| 10,000 | 30,859.60032567703191584549 |
About Calories (th)/second (cal(th)/s)
Calories (thermochemical) per second (cal(th)/s) equals 4.184 watts. It is a caloric power unit used in thermochemistry and laboratory heat-flow measurements where energy is expressed in thermochemical calories rather than joules. Reaction calorimeters and bomb calorimeters sometimes report heat release rates in this unit. It is closely related to the watt but retains the calorie convention of chemistry rather than physics.
A 60 W light bulb dissipates about 14.3 cal(th)/s as heat. A vigorous chemical reaction releasing 100 cal(th)/s generates 418 W of thermal power.
About Foot pounds-force second (ft·lbf/s)
Foot pounds-force per second (ft·lbf/s) is the fundamental mechanical power unit in the US customary system, equal to approximately 1.356 watts. It is the rate of doing work when a force of one pound-force moves through one foot per second. The unit is directly related to the mechanical horsepower: one horsepower equals exactly 550 ft·lbf/s. It appears in US mechanical engineering, ballistics, and machinery design texts.
One mechanical horsepower equals 550 ft·lbf/s (~746 W). A person climbing stairs moderately expends about 200–300 ft·lbf/s of mechanical power.
Calories (th)/second – Frequently Asked Questions
Why do chemists use calories per second instead of watts?
Tradition and unit consistency. When your energy measurements are in calories (specific heat of water = 1 cal/g/°C makes calculations beautifully clean), expressing rates in cal/s keeps everything in the same system. A chemist measuring how fast a reaction heats 500 mL of water doesn't want to convert to joules just to report a rate. The calorie makes water-based calorimetry arithmetic almost trivial.
What is the difference between a calorie and a Calorie in this context?
The thermochemical calorie (lowercase "c") used in cal/s equals 4.184 joules. The food Calorie (uppercase "C" or kilocalorie) is 1,000× larger at 4,184 joules. So 1 food Calorie/s = 4,184 watts — roughly the power of a space heater. Nutrition labels use kilocalories but write "Calories" with a capital C, creating one of the most persistent unit confusions in science. When you see cal/s in chemistry, it's always the small calorie.
How many cal/s does an exothermic chemical reaction typically release?
It varies enormously. Neutralizing a strong acid with a strong base might release 0.5–5 cal/s in a teaching lab. Combustion of magnesium ribbon produces 50–200 cal/s of intense white-hot heat. Thermite reactions can exceed 10,000 cal/s (42 kW). Explosive decomposition of TNT releases energy at roughly 250,000 cal/s (1 MW) during detonation. The rate depends on both the enthalpy change and how fast the reaction proceeds.
How do you measure heat output in calories per second experimentally?
A reaction calorimeter submerges the reaction vessel in a known mass of water and measures temperature rise over time. If 1,000 g of water rises 0.5°C in 10 seconds, the heat release is 500 cal in 10 seconds = 50 cal/s. Modern isothermal calorimeters use Peltier elements to maintain constant temperature, measuring the electrical power needed to compensate — giving cal/s readings with milliwatt precision.
Is the thermochemical calorie still used in modern research?
Increasingly rarely. IUPAC officially recommends joules, and most modern journals require SI units. However, the calorie persists in biochemistry (metabolic rates), nutrition (food energy), and some physical chemistry subfields where decades of reference data are in calories. Older researchers and textbooks still think in calories. The 4.184 conversion factor is burned into every chemist's brain, even if they wish it weren't.
Foot pounds-force second – Frequently Asked Questions
Why is horsepower defined as exactly 550 ft·lbf/s?
James Watt calculated that a mill horse could turn a mill wheel 144 times per hour, doing 32,572 ft·lbf of work per minute — he rounded up to 33,000 ft·lbf/min (550 ft·lbf/s) for marketing purposes. He wanted to sell steam engines by comparing them to horses, so he likely overestimated the horse to make his engines look like better value. A real horse sustains closer to 350–500 ft·lbf/s, so Watt's "1 HP" is actually more than one horse.
How do you calculate ft·lbf/s from torque and RPM?
Power (ft·lbf/s) = Torque (ft·lbf) × RPM × 2π / 60. This is the workhorse formula (pun intended) of US mechanical engineering. For example, an engine producing 200 ft·lbf of torque at 3,000 RPM delivers 200 × 3,000 × 6.2832 / 60 = 62,832 ft·lbf/s ≈ 114 hp. The formula works because angular velocity in rad/s times torque in ft·lbf gives power directly in ft·lbf/s.
What everyday forces produce 1 ft·lbf/s of power?
Pushing with 1 pound of force at 1 foot per second — roughly the effort of slowly sliding a light book across a table against friction. Lifting a 1-pound weight 1 foot in 1 second. Turning a doorknob with a very light touch. It's about 1.36 watts — enough to dimly light an LED. In human terms, it's almost effortless: casual walking produces about 50–80 ft·lbf/s of mechanical power, and you don't even notice.
Is ft·lbf/s still used in modern American engineering?
Yes, particularly in ballistics (muzzle energy rates), mechanical testing (dynamometer output), agricultural machinery specs, and industrial equipment designed for the US market. However, even in the US, many engineering firms are switching to SI units for international compatibility. The automotive industry increasingly quotes power in both hp and kW. Aerospace has been mostly metric since the 1990s. Ft·lbf/s survives mainly in traditional mechanical and manufacturing industries.
How does ft·lbf/s relate to bullet kinetic energy?
Bullets are rated in ft·lbf of muzzle energy (not per second), but the power of a firearm is the muzzle energy divided by barrel time. A .308 rifle bullet exits with about 2,600 ft·lbf of energy over a barrel transit time of ~0.001 seconds, meaning the instantaneous power is roughly 2,600,000 ft·lbf/s (about 3,500 hp). That's why rifle recoil feels punchy — for a millisecond, you're absorbing the reaction force of a truck engine.