LESSON hat is density? 24

Transcription

1 LESSON hat is density? 24 Rocks are heavy. A small box of rocks has a large. Yet a box of the same size containing corks has a small. How can objects that are the same size have different es? Scientists explain it this way: All matter is made up of atoms. All atoms have. Some matter has more ive atoms than others. The more ive the atoms, the greater the. Matter has. It also takes up space. The amount of space that matter takes up is called. The atoms of some kinds of matter are more tightly packed than the atoms of other kinds. More atoms in a mean more in that. Two properties of matter are important in the pull of gravity: the of each atom the number of atoms in a given The of a given of matter is called its density. It is the differences in densities that give objects of the same size different es. For example, gold is about twice as dense as copper. This means that if a piece of copper has a of 50 grams, then a piece of gold the same size would have a of 100 grams. How do you figure density? It is easy. Use this simple formula. Mass Volume

2 FIGURING VOLUME Volume is measured in cubic units. One common cubic unit is a cubic centimeter (cc). The of an object shaped like a box can be found by multiplying three numbers: length x width x height. Example: What is the of a box 5 centimeters long, 3 centimeters wide, and 2 centimeters high? = 1xwxh =5cm x3cm x2cm (55x3x2=30) = 30 cubic centimeters t M length 5cm Figure A 0 This means that 30 one-cubic centimeter boxes can fit inside this box. Figure B FIGURING DENSITY Now let us say that this same 30 cubic centimeter box has a of 120 grams. Let us find its density. 120 grams (g) 30 cubic centimeters (cc) ( = 4) 4 grams per cubic centimeter (4 g,' cc) Another.v y of saying this is: Each cubic centimeter of this substance has a of 4 grams. I cm Figure C

3 COMPARING DENSITIES Equal s of different substances have different es. Each one of these cubes has a of on :uhic cwcntimeter. Each substance has a different. Each substance has a different density. 2.7 grams 7.9 grams i gram 19.3 grams.5 grams.9 grams Figure D Answer these questions. 1. Which substance has the greatest density? 2. Which substance has the lowest density? 3. Iron, aluminum, and gold are metals. Which of the metals has the greatest density? 4. Which of the metals has the lowest density? 5. Anything that is Less dense than water will float. Which two substances will float on water?

4 UNDERSTANDING DENSITY Figure E shows a solid iron cube and a solid aluminum cube, Study the figure. Then fill in the blanks. iron 2 cm --- stuminurn -2 cm--- Figure E 1. The of the piece of iron is cubic centimeters. 2. The of the piece of aluminum is cubic centimeters. 3. The s the same, are, are not 4. They have the same. do, d t 5. The has a greater. aluminum, iron 6. Iron is dense than aluminum. more, less 7. Aluminum is dense than iron. more, less 8. Iron is more dense than aluminum. sometimes, always 9. Aluminum is less dense than iron. sometimes, always 10. Things made of iron are more ive than things made of aiuminum. always, sometimes 11. Things made of aluminum have a greater than things made of iron. can, can never These are tricky, Think before answering!

5 UNDERSTANDING VOLUME AND DENSITY Figure F 1. We know that iron is dense than aluminum. more, less 2. A of iron has than an equal of aluminum. larger, smaller Vow look at Figure F. 3. In Figure F the aluminum has a than the iron, larger, smaller 4. This mean that aluminum is more dense than iron. does, does not 5. The aluminum is more ive because there is a of aluminum than there is of iron. larger, smaller MATCHING Match each term in Column A with its description in Column B. Write the correct letter in the space provided. Column A - 1. density 4. length x width x height 5. vnlllrn^ Column B ula for density b) the amount of matter in a substance c) formula for d) the of a given e) the amount of space matter takes up

6 FINDING DENSITIES For each of the examples below, first, find the, Th -you. total 24 grams i find the density. The first one has been done aat 40 grams 2 cm length 4 cm 0 Figure G Finding Volume= Ixwxh Volume=4x2x 1 8 cubic centimeters (cc) Finding density 24 grams 8 cubic centimeters 3 grams/ cubic centimeter Figure H 2. Finding Volume= 1xwxh Finding density g grams/cc cc total 24 grams 71 total 500 grams 1 cm, CE 5cm 3cm 5 cm Figure 1 3. Volume=lxwxh cc - Figure J 4. I x w x h cc g Density.^. cc g/cc o/ec cc

7 TRUE OR FALSE In the space provided, write "true" if the sentence is true. Write "false" if the sentence i atse. All matter has and takes up space. 2. All atoms have the same. 3. An atom of iron is more ive than an atom of aluminum. 4. A pile of feathers can be more ive than a pile of rocks. 5. Density has to do only with. 6. Volume tells us how ive matter is. 7. Ice floats on water. 8. Ice is more dense than water. 9. Equal s always mean equal es. 10. A centimeter is a measure of. REACHING OUT A measuring cup or graduated cylinder measures liquid. One measurement of is the cubic centimeter. Another is the milliliter. One milliliter (ml) = one cubic centimeter. 1. What is the total of the rock and liquid in this graduated cylinder? 2. How can you use a graduated cylinder filled with water to find the of an odd-shaped object like a rock? Figure K