Issuu

Type:

Solution Manual

Resource:

College Physics Explore and Apply

Edition:

2nd Edition

Author(s):

Eugenia Etkina Gorazd Planinsic Alan Van Heuvelen

Chapter 1 Introducing Physics

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Chapter 1

Introducing Physics Activities in this chapter are supposed to be done on the first day of class to put students at ease, let them collaborate in groups and to reflect on the process that is depicted in the textbook in Figure 1.3 on page 4 which is the logical flow of concept development that we follow constructing all concepts in the course. We suggest doing 2 of the proposed activities, the first one and one of the others.

1.1 What is physics? (Devising and using new models) 1.1.1 Tennis rackets Class: Equipment per group: whiteboards and markers

Imagine that a new acquaintance (Miha) invited you to his house. You walk in and notice that he has 10 tennis rackets in the hall way. You wonder WHY Miha would have those rackets. Unfortunately, Miha does not speak English and cannot answer your question directly. Work with your group members to come up with a plan to find out why Miha had 10 tennis rackets. Ask your students to get in groups and make a list of possible explanations (see possible explanations in chapter 1 of the textbook). The most common ones are that Miha fixes rackets, or has 10 children, or is a coach, or is a tennis racket thief. After the groups put their possible explanations on the boards, ask them to share their ideas. After that, ask them how they can figure out which one is the real one. This is when the students will come with what we call “testing experiments”. Although, they might not look like experiments in physics, they need the same actions. For example, if they think that Miha has 10 children, they might suggest looking for different size shoes. The expect the shoes to be in the house if the children are there. This is the prediction. What if they go to the house and find the shoes? Does it mean Miha has 10 tennis rackets because of them or he can still be a repairman? But if they do not find any shoes there, they might be more convinced that children are not the reason. Eventually, they will need to agree that ruling out their explanations is easier than proving them. This is the goal of this activity.

Chapter 1 Introducing Physics

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1.1.2 Cool glass Class: Equipment per group: dry glass, ice-cold water, whiteboards, markers. Note: the higher the humidity in the room, more clearly visible will be the outcomes of the experiments (in our experience humidity of air should be 60% or higher). Alternatively, teacher may show slides with photos.

A teacher puts a dry and empty glass on the table and pours an ice-cold water into the glass. a. Carefully observe the glass for few minutes. Describe in simple words what you observe. Students will observe tiny water droplets that form on the outside wall of the glass. Make sure they DO NOT use the word “condensation”. b. Work with the members of your group to propose different explanations for the observed patterns. Try to devise as many explanations as possible. Put them on the whiteboard. In our experience, students propose up to four different explanations (see the first column in the table below). c. How can you find out which explanation is correct? In science we conduct testing experiments. A testing experiment is an experiment whose outcome you predict before conducting it using the idea under test. You do not need to agree with the idea but the prediction of the outcome must be based on it. After you design the experiment and make predictions based on all explanations that you devised, you will conduct the experiment and compare the outcome to the prediction. Work with your group members to propose testing experiments that you can run to test the proposed explanations. Try to propose as many as you can. The most frequently proposed testing experiments are described in the table below. d. For each testing experiment, make prediction for its outcome based on each explanation that you proposed in b. Indicate any assumptions that you made when making predictions. (Note: The best testing experiments are those that give different predictions for different explanations). See the table below. Predictions are given at the crossroads of the explanations and the testing experiments. Assumptions are indicated at the end of the testing experiments. d. Perform testing experiments that you proposed in b. (if necessary, ask teacher for additional equipment). See table below. Outcomes of the testing experiments are described in the row after the explanations. e. Compare the outcomes of the testing experiments with the predictions that you made in c. What can you say about the explanations under test now? Can you reject some explanations? Do

Chapter 1 Introducing Physics

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not forget to include the assumptions when making any judgements. Can you verify some assumptions? See table below. Judgments are given in the last row. f. Think of the explanation that you were not able to reject as a new piece of knowledge. Can you think of any application of this knowledge? Students usually come up with the following ideas: -Harvesting fresh water from air. Several simple devices that do this, and are actually used, can be found on the internet. -Drying air (for example in very humid places). Table 1.2 with solutions Testing exp. 1: Use dry, empty cooled glass (put glass in a fridge)

Testing exp. 2: Use different cold liquid (ex. oil)

Testing exp. 3: Put food coloring in ice-cold water

Testing exp. Testing exp. 5: 4: Cover the Weigh glass glass filled filled with ice- with ice-cold cold water water

Assumption: there is no water in oil

Assumption: food coloring goes through the glass but does not leave (evaporate from) water.

Assumption: the cover does not let water through

Explanation 1: Water from the glass seeped through glass wall

There will be no water outside glass

There will be colored water on outside glass.

mf = mi