Question

if you wanted to build a floating dock to be used on a freshwater lake, what material would you use and why? use evidence from the lab to support your answer.
density can be calculated by dividing the mass of the substance by the volume of the substance, d = m/v. what happens to the density if the mass stays constant (the same) but volume increases? provide a reason(s) to support why you think this happens.

Explanation:

Step1: Analyze floating - dock material

For a floating dock on a freshwater lake, a material with density less than that of freshwater (1 g/cm³) is needed. Common materials like treated wood (e.g., cedar or pine) can be used as they have densities around 0.3 - 0.8 g/cm³, allowing them to float. Also, high - density polyethylene (HDPE) is a good choice. It is durable, resistant to water and rot, and has a density of about 0.93 - 0.97 g/cm³, which is less than water's density, enabling it to float. In a lab, materials with known densities can be tested to see if they float in water samples similar to freshwater lake water.

Step2: Analyze density - mass - volume relationship

Given the density formula $D = \frac{m}{V}$, if $m$ (mass) is constant and $V$ (volume) increases, according to the rules of fraction division, the value of the fraction (density) decreases. For example, if the mass is 10 grams and the initial volume is 5 cm³, the density $D_1=\frac{10}{5}=2$ g/cm³. If the volume increases to 10 cm³ while the mass remains 10 grams, the new density $D_2=\frac{10}{10} = 1$ g/cm³. As the denominator of the fraction representing density gets larger while the numerator stays the same, the overall value of the fraction (density) becomes smaller.

Answer:

For the floating dock, materials like treated wood or high - density polyethylene can be used because their densities are less than that of freshwater, allowing them to float. When the mass stays constant and the volume increases, the density decreases because in the density formula $D=\frac{m}{V}$, an increase in the denominator $V$ while the numerator $m$ is unchanged results in a smaller value of the fraction (density).