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# Flow Rate And Viscosity

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## Tanvir 1D

on 12 March 2015

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#### Transcript of Flow Rate And Viscosity

Flow Rate
The dictionary definition of flow rate is a measure of how quickly fluids move; measured in a volume per unit time (ex: L/s). The flow rate can be affected by the fluid that is moving. For example if the fluid is honey, it would move slower than water because of the thickness. Can you think of two other substances that would move slower than water? Also, the opening of the pipe can control the amount of water that comes out of it. The force pushing that water would make a difference in the flow rate and if the surface of the pipe is smooth it would allow the water to move faster. Therefore, flow rate helps us measure how fast or slow a fluid moves.
1. (a) In your own words, define “flow rate” and “viscosity.”

(b) Describe the relationship between fl ow rate and viscosity
Cohesion
The textbook definition of cohesion is a measure of how strongly the particles of a fluid attract each other. Its like a force. They will stick together. For an example, some fluids such as caramel are so viscous that they will fold over on themselves. But some substances like water or milk show less cohesion, so they flow faster and freer. Also, gases are the least viscous fluids since their particles are the furthest away from each other. Can you think of other substances with less cohesion? Therefore, less viscous fluids are thin and runny and have a faster flow, and thicker fluids are more viscous and have slower flow rates.

Surface Tension
Surface tension is the force that causes particles on the surface of a liquid to be pushed together and form a layer. You can see the surface tension at work when you see a drop of water. It creates a little bead of water like a little dome. Surface tension is what makes the domes shape, and water doesn't flatten out. Surface tension has the dimension of force per unit length. The force of attraction among the water particles is greater than the force of gravity pulling a strider down on the waters surface. Also, water has cohesion and sometimes it needs to be reduced. When fire fighters are fighting forest fires, they can add a "wetting agent" to decrease the cohesion. This wetting agent lets the water spread more easily. The water with less cohesion spreads out when it hits the trees and ground. Can you think of another real life example of surface tension? Therefore, surface tension is particles that form a liquids surface.
Viscosity
Viscosity is the resistance of a fluid to flow. Two examples of fluids are water and helium. Some fluids have a high viscosity and some have a low viscosity. The viscosity depends on how fast or slow the fluid flows. As the temperature of the liquid increases, the particles of the liquid move faster and the viscosity decreases. If the temperature of liquid decreases, the particles slow down, which causes the viscosity to increase. Basically, if the liquid was warmer it will flow faster and if a liquid was cooler it will flow slower. Can you think of a fluid with a warmer temperature and a fluid with a cooler temperature? It is a bit different for gas. If the temperature of the gas increases, the viscosity increases because as the gas increases, the speed of the particles also seems to increase. Since the particles are speeding up, they start to collide causing friction to increase. The higher the amount of friction, the higher the viscosity. A fluid with high viscosity has a large amount of internal friction. Internal friction is the force that has a resisting motion. If the temperature of a gas decreases, the speed of the particles slows down and they collide less. This lowers the amount of friction which decreases the viscosity. The thickness of the fluid also takes a part of viscosity. Thinner fluids flow quicker which means they have a low viscosity. This means that thicker fluids flow slower and have a high viscosity. Therefore, viscosity resists a fluid to flow.
Flow Rate And viscosity
By: Tanvir B, Harishini, Cara, Avinash, And Aaron
1a) Flow rate is how fast a fluid moves. The flow rate can depend on several factors. These factors are the type of fluid that you are using, the force that is pushing on a fluid, the size of the pipe the fluid flows from and the type of surface the fluid flows over.
Viscosity is the resistance of a fluid to flow. There are two factors that determine the viscosity. The two factors are cohesion and adhesion. Thicker fluids flow slower than thinner fluids.
b) The flow rate and viscosity are connected because the viscosity of the fluid affects the flow rate. If a fluid has a low viscosity, it means that there will be a high flow rate. If a fluid has a high viscosity, it will have low flow rate.
2.) In your own words, describe "cohesion" and "surface tension"
Cohesion shows how greatly the particles are attracted to each other. Less cohesion means that the fluid will flow more freely. Surface tension describes the particles that create the surface of a liquid.
The textbook definition of Adhesion is "the attraction between the particles of one substance and the particles of another substance." Fluids that have slow flow rates have particles that have greater cohesion. An example of this is maple syrup. Can you think of another example? An example of adhesion is when you finish drinking a glass of milk, there is a thin layer of milk on the bottom and sides of the glass and your skin. Particles of fluids stick to the sides of containers, pipes and tubing. The adhesion between water and a container is responsible for creating the curved top surface you see when water touches the side of a container. This surface is called a meniscus. The cause of gases and liquids to travel faster near the center of pipes and tubes instead of at the edges is adhesion. The attraction of fluids to the material of pipes and tubes slows the flow of the fluid. In a similar way, water in a stream or river flows faster in the center instead of at the edges. Therefore, adhesion attracts between particles of two substances. ,

3.) Use the term "viscosity" to explain how wetting agents are used to help fires.
If the water that is used to put out the fire decreases in viscosity, that means the wetting agent is added. When you add the wetting agent to flow it spreads faster when it hits the trees and ground. When a liquid has less viscosity, it flows faster. Therefore, this is how viscosity is used in wetting agents to fight fire.
4.a) How does adhesion affect flow rate?

b) Give an example in real life that shows adhesion at work.