8 th Grade Science Chapter 2 Answers

Transcription

1 8 th Grade Science Chapter 2 Answers 1. Matter is anything that has volume and mass. Matter could be a chair, a mountain, or even a cloud. 2. Volume is the amount of space taken up, or occupied, by an object. *Remember, all matter takes up space regardless of its size, whether it is your diamond earring or The Statue of Liberty. 3. No, again, volume is the same regardless of the container you place the liquid in. If it is in you cup or a bowl, 8 ounces is still 8 ounces. 4. Meniscus is the curve at the surface of a liquid that you see when you measure the volume of the liquid. 5. You must take into account the meniscus that forms. This is a curve at the surface of the liquid and as a result can cause an inaccurate reading. Instead, you must look at the bottom of the meniscus (curve) to get an accurate reading. See Figure 3, page Volume of a solid is measured in cubic meters (m³) or cubic centimeters (cm³). Remember it must be shown as cubed because the measurement is the result of multiplying 3 quantities (sides) to get the final answer. 7. To calculate the volume of a solid you multiply the solids length x width x height cm x 35cm x 3 cm = 2100 cm³ see Figure 4 on page x 5 x 1 = 50 cm³ 10. You can compare the volume of a solid to a liquid. You would use the conversion that 1 ml = 1cm³. With this you are able to convert the measurement of a liquid to cm³ and thus make a comparison between the volume of a solid and a liquid. Remember you must make the conversion. Can you add, subtract or compare two fractions with different denominators (1/2 + 1/3), no you must find the common denominator first. Compare volumes of solids and liquids is the same thing. You must compare apples to apples. 11. A gas will actually fill the container that it occupies. Think of filling a balloon with helium, the balloon will grow to a particular size and shape based on the amount of gas that you put inside. Because of this, it is easy to measure the volume of a gas. If you know the volume of the container you are using then you can determine the volume of the gas, as they are one in the same. 12. Mass is the amount of matter that something is made of. Remember, even the smallest speck is made of matter and therefore has mass. 13. Matter and mass can be both constant and changing, it just depends on the item. If you are talking about a bowling ball- yes, as long as you do not smash it. But if you are talking about a baby, then no. The baby will grow and as it grows its matter and mass will change. See Figure 5 on page Mass considers only the matter within something, the objects stuff. Weight on the other hand takes into account gravity. An objects mass will stay the same, but the weight will change based on the gravity or gravitational force that is exerted on it. 15. Gravity is a force of attraction between objects that is a result of their masses. 16. The amount of attraction between objects depends on: a. The mass of the objects

2 b. The distance between them Imagine 2 giant magnets the size of dinner plates and place them 5 feet apart. There attraction will be strong. Now take those same magnets and move them 50 feet apart. The attraction will be significantly less. Now, do the same experiment but take magnets that are the size of a quarter and place them 5 feet apart. There will be an extremely small attraction between the two. Now take those same magnets and move them to within 5 inches of each other. Now the attraction will be significant. *Overall, to increase the attraction between 2 objects you would need to either increase the size of the objects or decrease the distance between them. See Figure 6 on page Weight is the measure of the gravitational force that is exerted on an object. Remember! Weight depends on mass, but weight and mass are NOT the same thing. 18. Think about the sponge vs. brick example in Figure 7, page 40. The brick and sponge are the same size, but their masses are different. The mass of the brick is significantly more than that of the sponge. For this reason the gravitation pull on the brick is significantly more than that of the sponge, so it weighs more. So, the greater the mass, the greater the gravitational force, and the Greater the Weight! 19. Distance plays an important role in calculating the gravitational force between objects. Remember that earlier we said that the closer the objects are to one another, the greater the gravitational pull. Like the magnet example, the gravitational pull is much greater if the objects are 5 ft away from versus 50 feet away from each other. So an object on Earth has a stronger gravitational pull than that same object would have out in outer space. 20. The SI unit for mass is kilogram (kg), however sometimes it is expressed in grams (g) or milligrams (mg). Remember, each of these units is based on a unit of Because weight is a measure of gravitational force, it must therefore be expressed in units of force. The SI unit of force is the Newton (N). 22. A Newton is approximately equal to the weight of 100g of mass on the Earth. 23. Mass is a measure of the amount of matter in an object, weight is a measure of the gravitational pull on that same object. In general, mass remains constant for an object no matter where that object is in the universe. Weight on the other hand will vary depending on where the object is in the universe. In general the weight will remain constant on Earth, because the gravitational pull on that object from the Earth is the same. A balance is used to measure mass and a spring scale is used to measure weight. Mass is measured in kilograms while weight is measured in Newtons. See Figure 8, page Inertia is the tendency of all objects to resist any change in motion. For this reason, we know that an object at rest will remain at rest until something causes it to move. Likewise, an object in motion will continue to move at the same speed and in the same direction unless something acts on it to change its speed or direction. 25. Mass is a measure of inertia. This is because an object will a large mass is much harder to move from a position of rest and harder to stop once in motion. So inertia will increase as mass increases.

3 26. A physical property of matter is something that can be observed or measured without changing the identity of the matter. Think of the 20 Questions example. You are asking about or observing the objects appearance; color, size, shape, etc. 27. See table on page 44 for the answer. Make sure you know more than a definition. Make sure you are able to apply what you know. 28. Density is the amount of matter in a given space, or volume (remember volume is defined as the amount of space taken up by an object.) Therefore the more matter an object has, the greater the density. Think of the golf ball/ping pong ball or brick/sponge examples. Both are nearly the same size, but the golf ball and brick have a greater amount of matter, so therefore they have a greater mass. 29. The formula for calculating density is D = M or Density = Mass V Volume The units used to express density are: mass unit or grams or kilograms volume unit cm³, mol, m³, L which means you might have g/cm³ or g/ml or kg/m³ or kg/l Know how to use this formula and be able to solve for any variable. 30. Find the density of a substance with a mass of 5 kg and a volume of 43 m³ D = M V D = 5kg 43m³ D = kg/m³ Go through and redo the homework you were assigned. Use your corrected homework as an answer key. 31. Density is used for 2 reasons: first, the density of a particular substance is always the same at a particular given temperature and pressure, regardless of the size of the sample. Two, the density of one substance is usually different than that of a second completely different substance. Meaning, no two substances will have the same density. 32. A great way to compare the densities of liquids is to place them in some sort of glass jar and watch the items separate. Look at Figure 12 on page 46. It shows (using coloring) how the different liquids with the different densities automatically separate themselves out into different layers. If you were to shake up the jar they would mix up, but as soon as you placed it back on a table, they would all separate out again. 33. Yes, the densities will be the same. Remember no matter the size of the sample, as long as it is the same substance at the same temperature and pressure, in this case helium, the density will remain the same.

4 34. A grease separator works because of the different densities of the liquids in the meat juices. The actual juice is denser than the grease and therefore it sinks to the bottom of the separator. By placing the spout at the bottom, you are able to pour off the juice for gravy, leaving the grease behind. 35. A chemical property describes a substance based on its ability to change into a new substance with different properties. Meaning, new physical properties as well as chemical ones and an inability to be changed back into the separate substances used to make it. 36. A chemical property is only able to be observed when one substance might become a new one. For example while a piece of wood is burning. You can only see the chemical change as the wood is burning. 37. The characteristic properties of a substance are always the same whether the sample is small or large. Scientists rely on these characteristic properties to identify and classify substances. 38. The characteristic properties are density, solubility and reactivity. 39. The Blimp flies because it is filled with Helium. Helium is a gas that has a density less than air, therefore it will rise relative to the air. Helium is also used because it is nonflammable (will not go up in flames.) Early Blimps used Hydrogen, a highly flammable and dangerous gas. 40. Define whether the following properties are chemical or physical: less dense than air does not react with vinegar: chemical malleable: physical flammable: chemical is white: physical your ice cream melts: physical the cup your hot chocolate is in is hot to the touch: physical your trucks bumper reacts to the air: chemical you bleach your blue sweatshirt: chemical you shave off a piece of soap: physical you make sugar water: physical 41. Yes, a physical change only ever changes the appearance of a substance, not its chemical make-up. For example, if my ice cream melts, I can put it back in the frig to refreeze it. If I make sugar water and the sugar dissolves, I can still go ahead and filter the water and separate the water and sugar. 42. A chemical property describes a substance s ability to go through a chemical change. If you take the example of wood burning, we state the wood is flammable or reacts with oxygen. Another way to state it is that the wood and oxygen are reactive. A chemical change however is the actual process by which that substance changes into another substance. For example the process of burning wood or when your iron bumper rusts after reacting with oxygen. 43. When baking cookies you not only combine the ingredients but by adding the heat source you bake them. Adding the heat actually causes a chemical reaction and turns all of your raw ingredients (flour, sugar, eggs, vanilla and butter) into a brand new, delicious treat.

5 44. The individual ingredients have their own unique set of physical properties, such as color, state, and malleability and chemical properties, such as reactivity with vinegar or flammability. Once you bake the cookies the ingredients have changed their state and no longer retain their original physical properties, instead they now have their own new set of properties. For example, the cookies are not as malleable as the butter was and are not white like the sugar or a liquid like the vanilla. 45. No and Yes, In general a chemical change causes an entirely new substance to be formed and can not be undone. Can you unbake the cookies or turn sour milk back into fresh milk? However there are a handful of chemical changes that can be reversed under the right conditions by the use of another chemical change.