Final answer:
Flow rate and fluid velocity are related through the cross-sectional area. Incompressible substances include water and oil.
Step-by-step explanation:
Flow rate is a measure of how much fluid moves through a particular point in a given amount of time, typically measured in volume per unit time (e.g., liters per second). Fluid velocity, on the other hand, refers to the speed and direction at which the fluid flows. Flow rate and fluid velocity are related through the cross-sectional area of the pipe or channel through which the fluid is flowing. As the flow velocity increases, the flow rate also increases, assuming the cross-sectional area remains constant.
When streamlines are closer together, it indicates that the fluid is flowing through a narrower channel or region. According to the principle of conservation of mass, the flow rate remains constant along a streamline. Therefore, if the cross-sectional area of the channel decreases (e.g., due to a constriction like in a Venturi tube), the fluid velocity increases to maintain the constant flow rate.
Some examples of substances that are incompressible include water, oil, and metals. These substances have a negligible change in volume when subjected to pressure. Conversely, gases such as air and helium are compressible, meaning their volume changes significantly with changes in pressure.