Viscosity:
-A fluid’s resistance to flow and movement
-“thickness” of a fluid
-caused by the attraction between the fluid’s particles (strong attraction =
thick, more viscous, like corn syrup / weak attraction = runny, less viscous, like
water)
Hydraulics:
-closed system that uses LIQUIDS to do work
-pressure is applied to the liquid, the force is transferred through the liquid to
do work
-used in things like heavy machinery, especially since it is more efficient than
pneumatics
Pneumatics:
-closed system that uses GASES to do work
-pressure is applied and the force transferred through the gas to do work
-not as efficient as hydraulics because gas particles are farther apart than liquid
particles
-can be found in things like drills, office chairs, etc.
Density:
-the amount of mass in a certain volume of a substance (measured in g/mL)
-“heaviness” of a substance
-caused by how many particles are in a certain volume of a substance, so the
more particles, the denser it is.
1) Explain why solids that flow are not fluids.
- solids that flow are solids that “flow” like fluids.
BUT they:
-don’t take the shape of their container, instead forming piles.
-particles in these solids don’t flow past each other like they do in real fluids (think back to
student demonstration)
-the solids “flow” as pieces of solid, the particles don’t flow
2) Which fluid can be compressed more, liquid or gas. Explain your choice using the particle
theory.
-Gas is more compressible than liquid
-gas particles are farther apart than particles in liquid, so the spaces between gas particles are
larger
-when gas and liquid are compressed, there are more empty spaces for the gas particles to fill
-the liquid particles are already close together so there is little space for them to get closer
together
*remember, liquid particles still have some space (not no space) in between, all particles do…
3) Two items with the same mass are placed in identical water tanks. Item 1 displaces 50mL
of water. Item 2 displaces 65mL of water. Explain why there is a difference in the water
displaced. What can be inferred about the density of the 2 items?
-since the 2 items have the same mass, the difference in displaced water is caused by their
different volumes (space the item takes up)
-since item 1 takes up less space (lower volume, smaller), but weighs the same, it is denser than
item 2
-item 2 needs more space to have the same mass, so it is not as dense as item 1
4) An object is dropped into two types of fluids. In fluid A, the object sinks. In fluid B, the
same object floats. Using proper terms and particle theory, explain what happened.
-the same object is used for both, so the fluids have different densities
-fluid A is less dense than the object because the object has negative buoyancy (sinks) in it. This
means that there are more particles in the same amount of space (volume) of the object than
the fluid A. The buoyancy force of fluid A is not as strong as the forces pushing the object down
-fluid B is more dense than the object because the object has positive buoyancy (floats). This
means the fluid has particles in the same amount of space when compared to the object. The
buoyancy force of fluid B is strong enough to keep the object afloat
-the particles in fluid A are not as close together as the particles in fluid B, so fluid B is denser
and has a higher buoyancy force (since object is the same)
5) How would you use water displacement to find the mass of an object? (The density of the
water is 1g/mL)
-since the water displaced will have the same volume as the object, we can measure the amount of
water displaced by the object to find the mass
-we can take the volume of the displaced water and calculate (multiply the density by volume) or since the density of water is 1g/mL, we can say that the volume will be equal to the mass
*some people also explained step by step how to displace the water, collect, measure and calculate
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