Static Fluids Concepts and Questions
Static Fluids
Exert forces on any surface they come into contact with Pressure = Force / Area
The pressure that a liquid exerts on the bottom surface of a container is the net result of individual molecules in the liquid that collide with the surface. Which of the following correctly indicates and justifies the relationship between the force exerted on the surface by a molecule and the force exerted on a molecule by the surface during a single one of these collisions?
F(molecule on surface) = F(surface on molecule) because the force the molecule exerts on the surface is equal and opposite to the force the surface exerts on the molecule.
Which of the following helps explain why the buoyant force exerted on an object submerged in a fluid on Earth is always directed upward?
Fluid pressure is exerted on all surfaces of an object and increases with depth. The horizontal forces due to the pressure cancel, but the vertical forces do not.
A student has three objects of different shapes and wants to compare their densities using liquids of known density. Which of the following experimental methods will allow the comparison to be made?
Let each object float in the same liquid, and compare the fractions of the objects' volumes that are below the liquid surface.
A student has four pieces of a substance in different shapes and sizes. The student wants to determine the density of the substance. Which of the following procedures would yield the most accurate data?
Place the pieces on a mass balance, one at a time and record the mass of each. Submerge the pieces one at a time in a graduated cylinder filled with a volume of water and record the volume change.
Archemede's Principle (buoyant forces)
The buoyant force F(B) of a liquid exists because the pressure of a static fluid varies by depth F(B) = weight of fluid displaced F(B) = p(liquid) V(object) g
A cube of mass m with sides of length s is completely submerged in a tank of fluid of density r and held in place by a string attached to the bottom of the tank. The height of the fluid is h, and the string has a nonzero tension FT. Which of the following indicates how the density of the cube compares with the density of the fluid and provides correct evidence for the comparison?
The fact that there is tension in the string is evidence that the density of the cube is less than the density of the fluid.
A block of aluminum with a mass of 1kg is placed in a beaker of water filled to the brim and it sinks. Water overflows. The same happens in another beaker with a 1kg block of lead. What is true about the amount of water displaced?
The lead will displace less water
A student predicts that the density of salt water is higher than the density of drinking water. The student has a beaker filled with salt water, a beaker filled with drinking water, and a cube that is hung from a spring scale. The cube will sink in both liquids. What measurements are needed to verify the student's prediction?
The spring scale reading of the cube in each liquid only.
A jar contains vinegar and oil that have separated into layers. Which of the following correctly identifies a Newton's third law force pair?
The weight of the vinegar and the gravitational force of the vinegar on Earth
The pressure exerted on the bottom of a dam by the water in the reservoir created by the dam depends on the
depth of the water at the dam
An object floats or sinks if..
p = density p(object) < p(liquid) = object floats p(object) > p(liquid) = object sinks p(object) = p(liquid) = object is suspended in liquid, forces are balanced
