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2. Safety is very important in science to keep students safe and healthy. It is also important to keep from damaging equipment and supplies.
4. To make an informed decision, the students need to know how much each light bulb costs and how long each light bulb lasts. If they know these things, they can compare the savings with the longer life. Saving $0.50 on a light bulb that costs $2.00 is probably better than getting an extra 30 hours from a light bulb that lasts 3000 hours. But, if the light bulbs are more expensive or last a shorter time, then the longer light bulb life might be a better deal than saving $0.50. They cannot tell, though, without knowing the price and life of each bulb.
6. The three kinds of variables are independent variables, dependent variables, and controlled variables.
8. A hypothesis is a special kind of prediction. It is an education guess about the relationship between variables. It can be tested with a scientific investigation. A hypothesis can be written as an If, Then statement.
10. Tools help scientists make observations that are accurate and precise.
12. It is important for scientists to communicate date so that other people can learn from them.
Also, communicating results lets other scientists repeat the experiment and verify it.
14. Models let scientists observe things that are too big, too small, too expensive, or too dangerous to observe otherwise.
A globe is a model
16. limit the number of variables being tested
conduct enough trials to get sufficient data
eliminate bias
prepare good data tables
consider safety
measure carefully
18. One conclusion is that the hotter water is, the faster it cools. For the 200 mL samples, the hotter sample lost 22 °C, and the cooler one lost 14 °C. For the 400 mL samples, the hotter one lost 13 °C, and the cooler one lost 8 °C. Another conclusion is that larger volumes of water cool more slowly. For the samples at 80 °C, the larger one lost 13 °C, and the smaller one lost 22 °C in the same amount of time. The cooler water samples followed the same pattern.
22. The tools needed for this experiment are magnets of different sizes, small objects that could be attracted to the magnets, and a measuring device such as a balance or spring scale. To collect data for this science experiment, students will need to know both the size and strength of different magnets. They could measure how many quarters can be suspended from each magnet. The data would be placed in a chart for comparison. The chart may look like this:
Magnet Mass (grams) Number of paper clips held on one end
1
2
3
24. The scientist was trying to test the hypothesis: A plant needs light to grow. The experiment helps the scientist test the hypothesis because there are two plants that started out the same. The scientist placed one plant in the sun and the other in the shade to test the hypothesis while keeping the other variables constant in the experiment. This design limits the variation between the plants to the amount of light received by each plant.
26. Hypothesis: The rate of breathing increases based on the number of laps Stephanie swims.
If the number of laps increases, then the breathing rate will increase.
Experiment: Stephanie can find out how many breaths she takes per minute while resting. She can then swim 5 laps and count the number of breaths she takes per minute. Stephanie can then rest until her breathing is back to a normal resting amount and swim 10 laps and count the number of breaths she takes per minute. She can continue these steps for up to 30 laps. During each test, Stephanie should swim at the same speed. Independent variable: number of laps Stephanie swims Dependent variable: breathing rate per set of laps
28. Most of the trees increase came from something other than the soil
30. The electrical cord of the hot plate should be checked before plugging in the hot plate because a frayed cord could lead to an electric shock.
32. All of the solutions from the students are potentially dangerous. Amanda wants to taste each solution. Because the powders were unknown, she can't tell whether the liquids are poisonous. Tasting the liquids could make the students sick. Kai wants to try mixing chemicals with the liquids to test their reactions. Because she doesn't know what the chemicals are, Kai can't be sure what the reactions will be. The reactions could be explosive or release toxic fumes. Damon wants to get a Bunsen burner and boil each liquid. Because he doesn't know what the liquids are, Damon can't predict how they will react to being heated. He can't tell whether the liquids are flammable. To solve their problem, the students should let the teacher know what happened and see if there is a safe way to figure out which liquid is which. If not, they may need to repeat the experiment.
34. Brand one is misleading because it says that it is water resistant, but if you have to reapply it after swimming and sweating, it is not waterproof under the conditions most users would use it for. It is also misleading because it says it is pediatrician tested, but it does not say what the results of the test were. It might have been tested and found to be inferior to all of the other brands that were tested.
36. The balance reading is 352 grams. Because the tray has a mass of 14 grams, the mass of the iron filings is 338 grams.
38. The volume of the water is 35 mL. The volume of the rock is 17 mL. One characteristic of the rock that can be observed is its small size. It must be small to fit into a graduated cylinder. Also, the rock has different minerals in it. You can see them in the light and dark patches on the rock's surface.
40. A double line graph is best for this data because the students are working with two groups of plants and want to show how each group changes over time.
42. The density of the rock is 4 g/mL. I determined the density by dividing the mass of the rock by the volume of water that it displaced in the graduated cylinder. A ruler could not be used to find the volume because the rock has an odd shape.
44. One variable that must be controlled is the mass of each metal used in the experiment. The student must use equal masses of iron, copper, and aluminum. This is because a larger mass can hold more heat. This means it would have more heat to transfer to water. Another variable to control is the temperature to which each metal is heated. If a metal were heated to a higher temperature, it would have more heat to transfer to the water.
46. The student used 42 mm as the measurement and didn't take into account that the block didn't start on the 0 mm mark. The actual block length is 29 mm.
48. In this experiment, the concentration of salt in each solution is the independent variable. This is the variable that the student changes deliberately in each sample. The boiling point of each solution is the dependent variable. This is the variable that the student hopes to change by varying the independent variable.
50. The experiment should have 20 tomato plantsfive tomato plants for each type of fertilizer, and 5 control plants to be grown without fertilizer. Over several months, each plant would be given the same amount of water, sunlight, and fertilizer (except the controls, which only get water and sunlight). To analyze their results, students should count the total number of tomatoes produced by each group of plants. Students should use the fertilizer used by the group of plants producing the most tomatoes. If the control group produces the most tomatoes, students should not use fertilizer in their garden.
52. Each brand should be evaluated on its absorbency. Students should obtain 5 sheets of several brands of paper towel. Students should make sure each sheet is the same size. Each sheet can be dipped into a beaker containing 1 liter of water for 30 seconds. Then students should remove the sheet and record the volume of water remaining in the beaker. Students should subtract this volume from 1 liter to find the amount of water absorbed by the sheet. To determine which towel is more absorbent, the 5 test values for each brand should be averaged. If the local brand has the highest average value, its paper towels are the most absorbent.
54. Today, knowing about the Gulf Stream helps us to understand weather and climate. We know that the flow helps carry warm water from the equator along the Eastern United States and toward Northern Europe. Scientists know that hurricanes formed in tropical waters are likely to follow the Gulf Stream. This can help them predict which areas will be damaged by storms.
56. A judgment based on what has been observed in an experiment is a conclusion.
