Fluid Density

Fluids have a number of characteristics that can be used for identification, such as boiling point, freezing point, and viscosity. One of the most common properties used to identify a fluid is density. Can simply dropping various items in a fluid and some basic understanding of graphing be used to determine the fluid’s density? Don’t drop the ball, try out the simulation.

Planning and Carrying Out Investigations

Fluid Density Brochure

What is mass?

Mass is defined as the amount of matter in an object. Mass is typically measured in units of grams or kilograms. The mass of an object is constant and does not change based on the location of the object. An object that has a mass of 10-kilograms on Earth would have the same mass on the moon, but the object's weight would be about 1/6 its weight on Earth since the force of gravity on the moon is less than the force of gravity on Earth.

What is volume?

Volume is defined as the amount of space an object takes up. Volume has a wide variety of units of measure, including English measures of gallons, pints, and cubic feet; and metric measures of liter and cubic centimeters.

What is density?

Density can be thought of as the compactness of a material. The more compact the material, the higher the material's density. Density is defined as the mass of an object divided by its volume. Common units of density are grams per milliliter or grams per cubic centimeter.

Why do some objects sink and other objects float?

The sinking or floating of an object placed in a fluid depends entirely on the comparison of the density of the object versus the density of the fluid. A denser object will sink in a less dense fluid. A less dense object will float on a more dense fluid. If the object's and fluid's densities are identical, the object will hover in position at whatever depth the object is released in the fluid.

What information does the slope of a line provide?

The slope of a line provides information about how two variables are related. The slope is defined as the rise of the line (change in the "y" variable) over the run of the line (change in the "x" variable). A steep slope indicates that the "y" variable changes drastically, while the "x" variable changes much less. A near flat slope shows that the "y" variable changes little, while the "x" variable changes greatly.

How can a line graph be used to predict unknown values?

Graphs provide a way to quickly analyze the relationship between variables. Graphs are typically constructed using two axes, the "y" axis where the dependent variable is plotted and the "x" axis where the independent is plotted. A line graph is constructed by plotting each "x" and "y" value, then connecting each point with a line. Best fit lines are constructed by drawing the "average" line through the points without connecting each point. Values of x and y that were not collected in the data set can be estimated by choosing any point on the line and drawing a horizontal line to the "y" axis to determine the y value and dropping a vertical line from the point to the "x" axis to predict the x value.

Walkthrough

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Tier 2 Lessons: Grades 7 - 12+

Lesson 1

Does Size Matter?

Lesson 2

How Dense Is It?

You need to to access this simulation.

1. What is density?

A. mass divided by volume

B. force times acceleration

C. tension divided by strength

D. pressure divided by area

2. The density of a fluid cannot be found by using the same equation used for finding the density of a solid.

A. true

B. false

3. Which is denser, water in a solid state (ice) or water in a liquid state

A. ice

B. liquid water

C. they are both the same density because they are both H₂O

4. Why do boats made of steel float while bars made of steel sink?

A. Boats have to use propellers to keep from sinking, but bars of steel have no propellers.

B. Buoyancy is inversely proportional to size; therefore, the larger the object, the more likely it will float, which is why humans can float in a pool but pennies sink to the bottom.

C. Even though the mass of both may be the same, the volume of the boat is greater because there is more empty space, and therefore the boat is less dense than the water.

D. none of these

5. What does the slope of a line on a graph represent?

A. a ratio of two values, Δy over Δx

B. the distance from the origin to a given point

C. the product of y and x

D. the distance between two axes

6. A sphere with a density of 0.065 g/mL is dropped into a fluid with a density of 1.3 g/mL. What should happen to the sphere?

A. the sphere should float on the surface of the liquid

B. the sphere should hover in the middle depth of the liquid

C. the sphere should sink to the bottom of the liquid

D. cannot be determined

7. A line has a very steep slope. If the range of possible values of x and y are equal, which value should be larger?

A. Δx

B. Δy

C. Δx should be equal to Δy

D. cannot be determined

8. Which variable is normally placed on the "y" or vertical axis when constructing a line graph?

A. dependent

B. independent

C. moderator

D. control

9. Two objects, A and B, have different volumes. If the mass of object A is twice as large as the mass of object B, which statement is correct?

A. Object A is definitely denser than object B.

B. Object B is definitely denser than object A.

C. Objects A and B definitely have the same density.

D. The relative densities of the two objects (A and B) cannot be determined from this data.

10. The slope of the line on the graph below indicates the density of a liquid. An object is placed in the liquid. If the object sinks to the bottom of the liquid, which point on the graph may be a possible density of the object placed in the liquid?

A. point A

B. point B

C. point C

D. cannot be determined

11. Two objects, C and D, have the same mass. If the volume of object C is twice as large as the volume of object D, which statement is correct?

A. Object C is definitely denser than object D.

B. Object D is definitely denser than object C.

C. Objects C and D definitely have the same density.

D. The relative densities of the two objects (C and D) cannot be determined from this data.