Physical Science 8th grade (1).pdf

Figure 48 the key displaced 30 milliliters of water

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Figure 4.8: The key displaced 3.0 milliliters of water. 50 6 0 5 0 4 0 3 0 1 0 6 0 5 0 4 0 50 mL 53 mL 3 0 2 0 2 0 1 0 Volume Volume Volume is the amount of space an object takes up. The units used to measure volume depend on whether the object is solid or liquid. The volume of solids is measured in cubic centimeters (cm 3 ) or cubic meters (m 3 ). The volume of liquids is measured in milliliters (mL) or liters (L). One cubic centimeter is the same volume as one milliliter. Measuring the volume of liquids Measuring the volume of liquids is easy. Pour the liquid into a marked container called a graduated cylinder and read the volume. There are two things to keep in mind to measure accurately. First, read the mark at eye level. Second, you will notice that the surface of the liquid forms a curve rather than a straight line (Figure 4.7). This curve is called the meniscus. Read the volume at the center of the meniscus. Volume of solids You have probably already learned to measure the volume of some solid shapes. The volume of a rectangular solid (a shoebox shape), for example, is found by multiplying length times width times height. The volume of a sphere is 4/3 π r 3 , with r equal to the radius of the sphere. The displacement method You can find the volume of an irregular shape using a technique called displacement. To displace means to “take the place of” or to “push aside.” You can find the volume of an irregularly shaped object by putting it in water and measuring the amount of water displaced. How you make the measurement You can use the displacement method to find the volume of an ordinary item like a house key. Fill a 100-milliliter graduated cylinder with 50 mL of water (Figure 4.7). Gently slide the key into the water. The water level in the container will rise, because the key displaced, or pushed aside, some water. If the level now reads 53.0 mL, you know that the key displaced 3.0 mL of water. The volume of the key, or of any object you measured in this way, is equal to the volume of the water it displaced. The key has a volume of 3.0 milliliters, or 3.0 cubic centimeters (cm 3 ).
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79 4.1 D ENSITY C HAPTER 4: D ENSITY AND B UOYANCY Determining density Measuring density To find the density of a material, you need to know the mass and volume of a solid sample of the material. You can calculate the density from the formula below. Mass is measured with a balance or scale. For irregular objects (Figure 4.10) the displacement method can be used to find the volume. Calculating volume For simple shapes you can calculate the volume. The volume of spheres, cylinders, and rectangular solids is given in the diagram in Figure 4.9. When calculating volume, all of the units of length involved in the calculation must be the same. For example, if you want volume in cubic centimeters, all of the measurements in the calculation must be in centimeters.
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