Answers to Lessons #1-3 Grade 8 Matter and Energy

1

A fluid is a material that has no fixed shape and is free to flow (liquids and gases).

Define fluids in your own words.

Water 🡪 all organisms need water to survive

• Producers need water for photosynthesis

Oxygen 🡪 animals need to breathe oxygen in order for cells to survive

Carbon Dioxide 🡪 plants need carbon dioxide to produce sugar and oxygen (photosynthesis)

1. Name three fluids that are essential to life and justify your answer.

1. when water is a solid (ice), the particles are vibrating only slightly and are tightly packed

2. we add heat energy and the particles start to vibrate faster and spread apart and eventually vibrate fast enough to become a liquid (melting)

3. we add more heat energy, the particles vibrate even faster and move far apart and eventually move fast enough to become a gas (evaporation).

1. Use the particle theory of matter to explain the changes that a particle of water would experience as it changes phase from a solid to a liquid and finally to a gas.

Definite shape 🡪 solid

Definite volume 🡪 solid, liquid

1. Which phases of matter have a definite shape? Which have a definite volume?

The particles of a fluid must be able to move freely past each other in order to flow. Fluids flow in two main patterns (laminar and turbulent).

1. State two characteristics of all fluids.

The particles in solids are closely packed

which creates a definite shape and resists flowing. 

1. Use the particle theory to explain why fluids can flow and solids cannot.

Laminar flow is a smooth pattern of flow. Turbulent flow is an irregular, mixing pattern of flow.

What is the difference between laminar and turbulent flow?

	Laminar	Turbulent
Advantage	It allows fluids   to move quickly and with more energy - cheaper on gas	-Cools down things quicker - mixes things better
Disadvantage	Takes longer to cool things -Does not mix things well	Decreased energy efficiency  -More expensive on gas

1. What is one advantage and one disadvantage of each type of flow?

Laminar provides less air resistance (drag), which allows the car to travel faster and with less energy consumption (cheaper on gas).

When building a new car, the designer often tries to streamline the design to make it more aerodynamic. Use the ideas of laminar and turbulent flow to explain why this is helpful.

Another way to think of viscosity is the ‘thickness’ of the fluid or the ability of the fluid to flow.

Cohesion is the force of attraction between the particles of the same substance

Adhesion is the force of attraction between the particles of one substance and the particles of another substance

1. In your own words, explain viscosity, cohesion and adhesion.

1. The average shower is 8 minutes long and uses 62 L of water.

Flow rate = volume/length of time

          =62L/8min

          = 7.75 L/min

2. The average bath takes 5 minutes to fill and uses 80 L of water.

Flow rate = volume/length of time

          =80L/5min

          =16 L/min

Calculate the flow rate in the following situations.

1. Your tap flows at 2 L/min and you leave it running for the 2.5 minutes it takes you to brush your teeth.

     Flow rate = volume /length of time

Volume = Flow Rate x length of time

2L/min x 2.5min= Volume

            5L = Volume

2. Your garden hose flows at 140 L/min and it takes you 1.5 hours to water your lawn.

      Flow rate = volume/length of time

Volume = Flow Rate x Length of time    =140 L/min x 90 min

        = 12600 L

1.5 hours = 1.5 x 60 = 90 mins

1. Calculate how much water is used in each situation.

(Oil, water, alcohol)

	Viscosity	Cohesion	Adhesion
#1	Oil	Water	Oil
#2	Water	alcohol	Water
#3	Alcohol	Oil	alcohol

1. Choose three common fluids and list them in order of viscosity, cohesion and adhesion.

Adhesion causes fluids to flow faster in the middle of pipes rather than at the edges because the fluids stick to the pipes as they pass. Fluids also flow faster in the center of a stream than at the edges because the fluids stick (adhesion) to the sides (banks) and bottom of the stream.

1. Why do fluids travel faster in the center of pipes and streams than at the edges?

1. As viscosity increases, the flow rate decreases.

2. As cohesion increases, the flow rate decreases.

3. As adhesion increases, the flow rate decreases.

1. Complete the following statements using the words ‘increases’ or ‘decreases’.