Fluids

= Fluids = =Every object has a specific density. Density is independent from mass, for examle, an iron nail is more dense than a wooden log, despite the fact that the log clearly ways more. The equation for density is the following:= p=m/V where p is the greek letter rho, m denotes mass and V denotes volume. The units for density are kg/m^3. There is one specific density that we need to learn in AP physics, the density for water: 1.0x10^3 kg/m^3. The specific gravity of a material is the ration of density of the substance over that of water (as a liquid). For example the density of aluminum is 2.70 x 10^3, so the equation for the specific gravity is (2.70 x 10^3 kg/m^3) / (1.0 x 10^3 kg/m3) = 2.7 Pressure is force divided by area. P = F / A The main unit for presssure is pascal (Pa). It is necessary to note that pressure in a fluid is applied in every direction (scaler). For instance, think of how whenever you go swimming, you feel pressure upon your body, not just in the upward or downward directions, but in every directions. However, the deeper down you go, the stronger pressure grows; in other words, pressure increases with depth. An equation: P = pgh We use this value for the pressure of the atmosphere: 1atm = 1.013 kPa. Gauge pressure is pressure relative to the atmosphere, and it is relavent for tire gauges. In order to find the absolute pressure, one must add atmospheric pressure to gauge pressure. P = Pa + Pg Pascal's Principle = when external pressure is added to a confined fluid, the pressure at every pint within the fluid increases by that amount. Pascal's principle comes into play with hydraulic lifts, which use a small input force to to exert a large output force by making the area of the output piston larger than that of the input piston. Pout = Pin F out / A out = F in / A in or F out / F in = A out / A in This is an equation that you might find helpful: P = Pa + pg* delta h Where P is pressure, Pa is atmospheric pressure, and h is height.

Objects in water appear to weigh less than they actually do. This is because of an upward force called buoyancy. The buoyant force is caused by of the difference of pressures in an object. The bottom of the object has a greater depth, and therefore has a greater upward pressure than that of the top of the object which will have a downward pressure that is smaller because the depth is less. The net pressure will hence be upward, so the force will be upward too.

The equation of for buoyance is: Fb = p*g*A*(h2-h1) or Fb = pVg Archimede's Principle comes into play here: the buyant force on an object immersed in a fluid is equal to the weight of the fluid displaced by that object.