F = dwater * volume flow * vel = 374.4 lbm ft/s 2į = 374.4 lbm ft/s 2 divide by 32.2 lbm-ft/lbf-s 2 = 11.examine a situation without gravity, the force produced by a jet of water. Lbm and lbf are not the same - they are only of the same value in one situation, when dealing with gravity at sea level. QUESTION: An astronaut has a mass of 100kg (220lbs) what is his weight (force) if he is on earth? what if he was on a planet with the gravity of 5m/s^2 (16.4ft/s^2)? Force is measured using acceleration, mass, and speed. On the surface of earth, 1lbm exerts a force of 1lbf. In simple terms, a Newton is the System International (SI) unit used to measure force. One newton is equal to the force needed to accelerate a mass of one kilogram one meter per second per second. On the surface of earth, 1kg exerts a force of 9.81N. Looking at the last two points above, it is obvious that the newton is very different that the lbf Think of pound-force (lbf) as the force required to move a mass of 1lbm by 32.2ft/s^s Think of newton as the force required to move a mass of 1kg by 1m/s^2 Once you understand this concept well you can go on to familiarize yourself to using slugs. you will see lbm used in your text and in real life 99% of the time. I know it is the standard unit for mass and so is lbm. I will try to make it as simple as possible and will provide an example: The viscosity of liquids decreases rapidly with an increase in temperature, and the viscosity of gases increases with an increase in temperature. The unit of viscosity, accordingly, is newton -second per square metre, which is usually expressed as pascal -second in SI units. I'd suggest adopting sdl for (2) lbf with unit slug, the ambiguity of pound is an unusual punishment lb, lbs, lbm, lbf, lbf. The dimensions of dynamic viscosity are force × time ÷ area. Know the base units of your system, lbf will always be an ambiguity problem as long as it exists in its current symbolic form. In SI units, the force unit is the newton ($N$), and it is defined as the force required to accelerate a mass of $1\cdot kg$ at a rate of $1\cdot\fracĮssentially, (1),(2) and (3) are all dividing by 32.174049, however, it is when and how that makes all the difference.
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