Lab - Density. Question: How does the size of a sample affect density?

Transcription

1 Name: Lab - Density Date: Question: How does the size of a sample affect density? Introduction: Density is the term used to describe the relationship between the mass of an object and its volume. Under given conditions of temperature and pressure, the density of a material is constant. The density of any Earth material can be determined by measuring its mass and volume and using the equation: DENSITY = MASS VOLUME Objective: You will be able to calculate the densities of different materials and recognize that density is one of the most important properties of matter. Hypothesis: Write a statement about how you think the size of an object affects its density. Vocabulary: Mass: Volume: Discplcement: Procedure: Part A - Density of Solid Objects 1. Measure the mass of each object (to the nearest tenth) using a balance. Your answer will be in grams (g). 2. Find the volume of each object using the metric ruler and the equation: Volume = length x width x height (V = l x w x h) or by using the water displacement method. Round your answer to the nearest tenth of a cm 3 (ex.: 0.1cm 3 ) 3. Calculate the density of each object by dividing the mass by the volume (use the equation above - show all work and calculate your answers to the nearest tenth). 4. Record data on Report Sheet #1.

2 Report Sheet #1 Aluminum Bar Aluminum Block Wood Block Brass Mass Metal Sphere Black Sphere

3 Part B - Density of Fluids 1. Using a balance and graduated cylinder, determine the mass and volume of 5 samples of Fluid A and 5 samples of Fluid B. Record the mass and volume data on your data table to the nearest whole number. 2. Make a graph of mass and volume data for each sample: a. First, plot the data for the 5 samples of Fluid A as 5 separate points. Connect those 5 points with a line and label it Density A b. Second, plot the data for the 5 samples of Fluid B as 5 separate points. Connect those 5 points with a line and label it Density B 3. Calculate the density of each sample of each fluid and record the density in the data table (show all math work). Sample # 1 Mass (g) Data Table Sample A Volume Density Mass (g) (ml) A (g/ml) Sample B Volume (ml) Density B (g/ml) Show your density calculations here:

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5 Discussion Questions: 1. There is water on the pan of the balance as you measure the mass of an object. If you were to ignore the water, what would be the effect on your density calculation? 2. What is the effect of shape on the density of samples of the same material? 3. If you were to cut the aluminum bar in half, what would the density of each half be compared to the original density of the bar? 4. If you had a bathtub full of Fluid A, would the density of ALL of the fluid in the tub be the same as only 1 gram of the fluid? Explain Your answer based on the data from this lab. 5. Describe all the steps of a procedure that could be used to find the density of a gigantic boulder partially buried in your lawn without digging up the boulder. 6. Looking at the graph lines you constructed for the density of 2 fluids, what is the relationship between the slope (steepness) of the lines and the density of the substances? Conclusion: How does the size of an object affect its density? Discuss the results to your hypothesis.

6 Reading Comprehension - Density Read the portion of the article on Density below and answer the following questions based on the reading. Use complete sentences. 05/17/2005 Understanding Air Density and its Effects (excerpt) By Jack Williams, USATODAY.com In simple terms, density is the mass of anything - including air - divided by the volume it occupies. In the metric system, which scientists use, we usually measure density in terms of kilograms per cubic meter. The air's density depends on its temperature, its pressure and how much water vapor is in the air. We'll talk about dry air first, which means we'll be concerned only with temperature and pressure. The molecules of nitrogen, oxygen and other gases that make up air are moving around at incredible speeds, colliding with each other and all other objects. The higher the temperature, the faster the molecules are moving. As the air is heated, the molecules speed up, which means they push harder against their surroundings. If the air is in a balloon, heating it will expand the balloon, cooling it will cause the balloon to shrink as the molecules slow down. If the heated air is surrounded by nothing but air, it will push the surrounding air aside. As a result, the amount of air in a particular "box" decreases when the air is heated if the air is free to escape from the box. In the free atmosphere, the air's density decreases as the air is heated. Pressure has the opposite effect on air density. Increasing the pressure increases the density. Think of what happens when you press down the handle of a bicycle pump. The air is compressed. The density increases as pressure increases. Effects of air density on airplanes, baseballs, race cars More dense, or "heavier" air will slow down objects moving through it more because the object has to, in effect, shove aside more or heavier molecules. Such air resistance is called "drag," which increases with air density. Baseball players have found that home runs travel farther in the less dense air in high-altitude Denver than in ball parks at lower elevations. The reduced drag slows the ball down at a slower rate, which means it travels farther. Cool, dense air slows a race car, but some race cars gain from dense air. Cars designed from the wheels up for racing are really like upside down airplane wings that the air pushes down on the track, increasing their grip going around curves. Denser air pushes then down harder. Aircraft pilots don't do as well as baseball players when the air's density decreases. Lower air density penalizes pilots in three ways: The lifting force on an airplane's wings or helicopter's rotor decreases, the power produced by the engine decreases, and the thrust of a propeller, rotor or jet engine decreases. These performance losses more than offset the reduced drag on the aircraft in less dense air.

7 Pilots use charts or calculators to find out how temperature and air pressure at a particular time and place will affect the air's density and therefore aircraft performance. In general, these calculations don't take humidity into account since its affects are so much less than the others. When the air's density is low, airplanes need longer runways to take off and land and they don't climb as quickly as when the air's density is high. Air density also affects the performance of automobiles, with lower density decreasing performance in the same way it decreases the performance of aircraft engines. Turbochargers or superchargers are ways of increasing the density of the air going into an engine. The give autos more power on the ground and they allow aircraft to fly higher into thinner air than they would otherwise. 1. State the relationship between density and temperature. 2. State the relationship between density and pressure. 3. What does more dense air do to objects traveling through it? 4. Explain how cars benefit from more dense air. 5. Two cars (A and B) are identical in every way. Car A will be driven around the track on a hot day while Car B will be driven around the track on a much cooler day. Which car will travel faster? Use the information from the lab and the article to support your answer. Adapted from Exploration in Earth Science, The Physical Setting, United Publishing Company, Inc.

8 LAB #1 - Density (data for lab - to be used for all calculations) PART A - Solid Objects Aluminum Bar: Aluminum Cube Wood Block 2.5 cm 1.3 cm 0.5 cm 1.3 cm 1.3 cm 2.5 cm 2.5 cm 7.5 cm 2.5 cm Mass = 32.5 g Mass = 7.7 g Mass = 10.4 g Brass Mass Metal Sphere Black Sphere Mass = g Mass = 84.4 g Mass = 25.0 g PART B - Fluids Fluid A Fluid B Mass (g) Volume (ml) Mass (g) Volume (ml)