# Density Unit 2 Fluids. Mass We can measure mass by using a balance or a digital scale. We can measure mass by using a balance or a digital scale.

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Density Unit 2 Fluids

Mass We can measure mass by using a balance or a digital scale. We can measure mass by using a balance or a digital scale.

Volume Volume is a measurement of the amount of space occupied by the substance. Volume is a measurement of the amount of space occupied by the substance. How can we measure volume? How can we measure volume? 1. Liquids can be measured using a measuring cup or a graduated cylinder.

Volume 2. Gases can be determined by measuring the volume of the container it is in. 3. Irregular solids can be determined by immersing them into a beaker of water and measuring the volume of the displaced fluid. Displacement is the amount of space that an object takes up when placed in a fluid.

Volume 4. Regular solids can be determined by measuring the length, width, and height: V = l × w × h.

How to Calculate Density Density (D) = Mass (m) or simply, D= _m Volume V Density (D) = Mass (m) or simply, D= _m Volume V Or V= m and m = V x D Or V= m and m = V x D D

Sample Problem Find the density of a 10 g mass of a substance that has a volume of 2.0 cm 3. Find the density of a 10 g mass of a substance that has a volume of 2.0 cm 3. cm 3 D = m D= 10g = 5 g/ cm 3 2.0 cm 3 V 2.0 cm 3

Sample Problem You want to put 10.0 g of salt into a container. If the density of salt is 2.16 g /cm 3, what is the volume of the container if the salt completely fills it? You want to put 10.0 g of salt into a container. If the density of salt is 2.16 g /cm 3, what is the volume of the container if the salt completely fills it? V= m V= 10.0 g V= 4.6 g/cm 3 D 2.16 g/cm 3

Sample Problem What is the mass of 1500 mL of helium, if the density of helium is 0.0002 g/mL? What is the mass of 1500 mL of helium, if the density of helium is 0.0002 g/mL? m= D x V m= 0.0002 g/mL x 1500 mL m= 0.3 g

Changes in Density As Temperature Increases ↓ Particles Gain Energy ↓ Particles spread out ↓ Decrease in Density As Temperature Decreases ↓ Particles Lose Energy ↓ Particles closer together ↓ Increase in Density

Examples of Changes in Density Hot Air Balloons (intentional change) a gas burner that heats the air inside the balloon a gas burner that heats the air inside the balloon particles gain energy and spread further apart particles gain energy and spread further apart the density of air inside the balloon decreases (less dense than air surrounding the balloon) the density of air inside the balloon decreases (less dense than air surrounding the balloon) so it rises so it rises pilot controls the altitude of the balloon by controlling the amount of heat pilot controls the altitude of the balloon by controlling the amount of heat

Examples of Changes in Density Warm vs. Cool Tire Pressure (natural change) Tires on an automobile need more air during the winter than they do during the summer. Tires on an automobile need more air during the winter than they do during the summer.Winter as the temperatures decrease particles lose energy and take up less space. as the temperatures decrease particles lose energy and take up less space. the density of the air decreases, and the tire deflates a little the density of the air decreases, and the tire deflates a littleSummer increasing temperatures increases particle energy (spread further apart) increasing temperatures increases particle energy (spread further apart) air in the tire expands air in the tire expands tire inflates tire inflates

Examples of Changes in Density water in its three states – natural change Most substances are denser in their solid state than in their liquid state; water is an exception Most substances are denser in their solid state than in their liquid state; water is an exception when water freezes, it expands and its density decreases (this is why ice floats) when water freezes, it expands and its density decreases (this is why ice floats) otherwise, water follows the normal trend otherwise, water follows the normal trend

Examples of Changes in Density drying of wood (seasoning of wood) – natural change freshly cut wood from a living tree is much heavier than wood that has been cut and dried in the air freshly cut wood from a living tree is much heavier than wood that has been cut and dried in the air water evaporates and is replaced with air water evaporates and is replaced with air air is much less dense than water, so dry wood is less dense than moist wood (and easier to burn) air is much less dense than water, so dry wood is less dense than moist wood (and easier to burn)

Examples of Changes in Density salt water being easier to float in – natural change much easier to float in salt water than in fresh water much easier to float in salt water than in fresh water the density of salt water is greater than that of fresh water the density of salt water is greater than that of fresh water

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