# The Travel Time of Floatable Litter of Different Densities Influenced by River Flow Velocity
## 2 Materials and Methods
### Measuring Physical Characteristics of Floatable Litter: Mass, Volume, Size, and Density  
#### 2.3.1 Mass, Volume, and Size of Floatable Litter (FL)  
The mass of the selected FL was measured using the electronic mass balance. The standard unit was recorded in grams (g) but later converted to kilograms (kg) to comply with the density standard unit, kilogram per cubic meter (kg/m\({}^{3}\)). The volume of selected FL was measured using the basic volume formula (for geometrical objects) and water displacement method (for non-geometrical objects). This is because the FL were in various shapes, which were categorized into geometric shapes and non-geometric shapes. For geometric-shaped FL, the volume was determined using the basic volume formula as in Equation (1):  
\[\text{Volume, V}=\text{Length, L}\times\text{Width, W}\times\text{Height, H} \tag{1}\]  
Specifically, the rectangular-shaped formula was used, as most of the geometric-shaped FL are rectangular. The volume of objects with a cylindrical shape (i.e., aluminum can) was determined directly from the stated volume on the product label. For non-geometric-shaped FL, the volume was determined using the water displacement method as in Figure 2. \begin{table}
\begin{tabular}{c c c c c} \hline
**No.** & **Object** & **Info** & **Size** & **Weight (g)** & **Form** \\ \hline
8 & &
\begin{tabular}{c} Organic cotton material, \\ high water-absorbent Brand: \\ Mamy Poko L size \\ \end{tabular} & 12 \(\times\) 21 cm & 48.06 & \\
9 & &
\begin{tabular}{c} Cloth \\ \end{tabular} & 100\% cotton, T-shirt, S size & - & 103.90 & \\
10 & & \
\begin{tabular}{c} Cardboard \\ \end{tabular} &
\begin{tabular}{c} Paper material Box shape \\ \end{tabular} & 10.8 \(\times\) 10.8 \(\times\) 26.0 cm & 68.50 & \\
11 & & \
\begin{tabular}{c} Polystyrene foam \\ \end{tabular} &
\begin{tabular}{c} Rectangle solid shape \\ \end{tabular} & 28.3 \(\times\) 9.2 \(\times\) 2.5 cm & 25.72 & \\
12 & &
\begin{tabular}{c} Cigarette butt \\ \end{tabular} & - & - & 1.00 & \\
13 & &
\begin{tabular}{c} Polymer foam \\ \end{tabular} & - & 10.15 \(\times\) 29.4 \(\times\) 1.30 cm & 22.46 & \\
14 & & \
\begin{tabular}{c} Paper \\ \end{tabular} &
\begin{tabular}{c} Magazine-type A4 size, \\ 90 pages \\ \end{tabular} & 21.0 \(\times\) 29.7 \(\times\) 0.5 cm & 96.07 & \\
15 & &
\begin{tabular}{c} Wood board \\ \end{tabular} & Thin plywood & 29.2 \(\times\) 57.5 \(\times\) 0.3 cm & 277.29 & \\
16 & &
\begin{tabular}{c} Glass bottle \\ \end{tabular} & Brand: VSoy & 300 mL & 173.85 & \\
17 & &
\begin{tabular}{c} Slipper \\ \end{tabular} & Rubber material Size 6 & - & 55.60 & \\
18 & &
\begin{tabular}{c} Sanitizer bottle \\ \end{tabular} & Spray bottle type & 50 mL & 12.17 & \\
19 & &
\begin{tabular}{c} Face mask 3-ply \\ \end{tabular} & Brand: Mr. DIY, Adult size & 16.0 \(\times\) 8.0 cm & 2.60 & \\
20 & &
\begin{tabular}{c} Parcel bag \\ \end{tabular} & Brand: Ninja Van, M size & 26.0 \(\times\) 33.0 cm & 12.30 & \\ \hline \end{tabular}
\end{table} 
Table 1: Cont. The volume of non-geometric FL was calculated using Equation (2):  
\[\text{Vo}=\text{V1}-\text{Vm} \tag{2}\]  
where Vo is the volume of the object, V1 is the new water volume after the object is immersed, and Vm is the initial water volume. For non-geometric-shaped FL that floats in water, a 10 g weightage--a sinker--was tied to a thread and attached to the FL to make the FL sink and become fully immersed. The initial water volume, Vm, was recorded. Next, the sinker and FL which were tied together were lowered gently into the container to avoid splashing. The new water volume, V1, was recorded. The volume of FL was determined using Equation (3):  
\[\text{Vo}=\text{V1}-\text{Vm}-\text{Vw} \tag{3}\]  
where Vw is the volume of weightage. For FL with known volume (i.e., mineral bottle, aluminum can, glass bottle, body wash bottle, sanitizer bottle), the volume was recorded directly. The size of each selected FL was measured in at least two dimensions (height \(\times\) width) only to give a picture of the FL size.