SIA 81-3 Notes PDF

Mix and Flow of Matter Section 3.0 –The Particle Model of Matter can explain the properties of gases and liquids. 3.1 Viscosity and the Effects of Temperature Fluids can flow. How quickly they can flow is called flow rate. A substance's resistance to flow (how thick or thin it is), or viscosity, af...

Mix and Flow of Matter Section 3.0 –The Particle Model of Matter can explain the properties of gases and liquids. 3.1 Viscosity and the Effects of Temperature Fluids can flow. How quickly they can flow is called flow rate. A substance's resistance to flow (how thick or thin it is), or viscosity, affects flow rate. The internal resistance or friction between the particles of the substance determines the viscosity of that substance. Ketchup Soda pop More Viscous Less Viscous The more friction - the more viscous (thicker) a substance is. The higher the viscosity of a substance, the slower it flows. The Effect of Temperature on Viscosity Temperature has an effect on the viscosity of a substance. When thick syrup is When thick oil is poured over hot added to the engine pancakes, the syrup of a car, the oil thins becomes thinner and out when the engine runs over the sides of heats up. the pancakes. Olive oil is very thin Asphalt (road paving) (almost watery). To materials are heated make it a little thicker up (making them less it can be placed in viscous) so they can the fridge, where it's be poured easily viscosity can be before it hardens. increased. Viscosity can be easily measured using the ramp method. Pour different liquids down a ramp and time how long it takes for each of them to get to the bottom. The one that is the slowest will be the most viscous. Reminder: Increasing temperature lowers viscosity (makes it thinner) Decreasing temperature increases viscosity (making it thicker) 3.2 Density of Fluids Density is the amount of matter in a given volume. Every substance has a different density, because each substance is made up of different particles. The density of a substance depends on the particles it is made up of. When we talk about density, it's usually mass density we're referring to. The mass density of an object is simply its mass divided by its volume. Density depends on whether the object is solid, filled with air pockets, or something in between. Substances that have a higher density than the density of the substance it is placed in will sink; substances that have a lower density than the density of the substance it is placed in will float. Calculating Density Density is the mass of a substance divided by its volume, which changes as temperature changes. This is shown in the following equation form: Density (d) = mass (m) / volume (V) Density Calculations (Memory Method) This simple equation will help you figure out how to solve density problems: M dV Simply cover up whichever value you need to calculate and the other two are shown in their proper placement, be it to multiply or to divide. For example: cover up the M. This leaves you with d/V (ignore the fact that it is in the de- nominator). Density times volume will give you mass. You can also check it out by way of the units: (g / cm3) x cm3 cancels out the volume unit leaving grams, the desired unit for mass. solids: d = grams/cubic centimeters ( cm3 ) liquids: d = grams/milliliters ( mL ) (Figure 3-4 Densities of some common substances at 20o - SIA p. 43) One way to determine the volume of an irregular object is to measure its mass in air and then in water, subtract the second measurement from the first, and divide by the density of water. Another way to determine the volume of an irregularly shaped object is to submerge the object in a full container of water. The volume of the object equals the volume of water that overflows. Ships can float because they contain large volume of air. The overall density of the ship is less dense than water, so it floats. 3.3 Density, Temperature and Buoyancy Viscosity changes with temperature. Density does not change as long as the temperature remains the same. The particle model of matter states that for every substance, the number of particles in a given volume, remain constant, if the temperature is kept constant. As energy is added, the particles move more quickly and further apart, thus increasing the substance's volume. When this happens, the density of the substance (which is the mass to volume ratio) decreases because the mass remains constant, but the volume increases. One substance can have different densities, depending on the state it is in. Changing Density by Changing Concentration Objects that are less dense than 1g/ml float in water. The Dead Sea is one of the saltiest bodies of water on the Earth. When salt is added to water, there are more particles in a given volume, which increases the density of the water, allowing denser objects to float in the saltwater. Buoyancy is the When an object is in a liquid, the force tendency of a of gravity pulls it down. The liquid substance to float. itself has a force that acts against the Buoyant objects take force of gravity. This buoyant force up space in a fluid. pushes objects upward. Objects that pushing some of the are denser than water will sink fluid away or (negative buoyancy); objects that displacing it, causing are less dense than water will float them to float, because (positive buoyancy); objects with the the fluid pushes back same density as water will hover (or, against the force of be suspended - (neutral buoyancy), gravity. neither sinking nor floating.) Measurement of Buoyancy Force is a push or a pull on an object, and is measured in Newtons (N). The upward force of a fluid on an object is called its buoyant force, which is also measured in Newtons. Calculation of Buoyant Force Buoyant Force = Weight in Air - Weight in Liquid Applications of Buoyancy Figure 3.11 Buoyancy has important applications in transportation. (sia p.51) Ships are designed to float in all types of water, regardless of the density of the water. The marks on the left indicate fresh This is possible because of the Plimsoll Line water - while - which shows how heavily a ship can be loaded the marks on in different water conditions. the right are for saltwater. Hot Air Balloons – As the air inside the balloon is heated, it becomes less dense than the surrounding air. The buoyant force of the air will push the hot air balloon upwards, until the buoyant force equals the force of gravity.