Home Page Textbooks Physics: Principles and Problems Section 13.2: Forces Within Liquids

Physics: Principles and Problems

9th Edition

Elliott, Haase, Harper, Herzog, Margaret Zorn, Nelson, Schuler, Zitzewitz

ISBN: 9780078458132

Textbook solutions

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Section 13.2: Forces Within Liquids

Exercise 17

Solution 1

Solution 2

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Because alcohol vaporizes easily, there is
a very noticeable evaporative cooling
effect.

Result

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Rubbing alcohol has smaller specific heat than water so it evaporates more easily and therefore it would alleviate the high fever more quickly since there is no build of hot liquid.

Exercise 18

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The key in making the paper clip float is to prevent the surface tension of the water from breaking. You can do this by taking another paperclip and use it as a lever to lower the paperclip gently onto the surface of the water.

Exercise 19

Solution 1

Solution 2

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Yes, the two terms are being used in the same context as seen in physics.

Step 2

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Adhesive tape sticks to something besides tape. A cohesive group is a crowd of people who work together.

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Adhesive forces are between two different type of materials and because adhesive tape sticks to material other than itself this context is used in the same manner.

Cohesive forces are forces between the molecules of the same material so the term working as a cohesive group is used in the same context as in physics.

Exercise 20

Solution 1

Solution 2

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Adhesion is the force that occurs between unlike objects/materials. Alcohol has a higher adhesive attraction to the glass than mercury which is why it clings on to the surface of the glass.

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Cohesive forces of mercury are strong enough to overcome its adhesive force with glass eventually.

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Cohesive forces in alcohol are weaker than adhesive forces between alcohol and glass.

In the case of mercury it’s the other way around. Adhesive forces between mercury and glass are weaker than cohesive forces in mercury.

Exercise 21

Solution 1

Solution 2

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If the clip breaks through the surface of the water, it will sink. For the most part, objects that float will move back and forth with the surface.

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We know that paperclip wasn’t floating because it has greater density than water. It was on the surface exclusively because of surface tension. If we release the paperclip in the manner that penetrates the surface it would not come back up.

Exercise 22

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The concept of this is based on the concept of CONDENSATION. Let us first understand the concept of CONDENSATION and then we shall go back to the experiment to understand it.

Whether you realize it or not, there’s water in the air around you all the time. Instead of liquid water, it’s a gas called water vapor. Warmer air can hold much more water vapor than colder air.
When water vapor in the air comes into contact with something cool, such as the outside of a cold glass of lemonade, its molecules slow down and get closer together. When that happens, the gaseous water vapor turns back into liquid water droplets. That’s the concept of CONDENSATION…

Step 2

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Now lets go t the experiment and try to understand it:

1. Beth sat with a glass of cold water.
2. Jo suggested that the water had leaked from inside to outside.
3. But it’s not so…! It’s because of the concept of CONDENSATION.

Step 3

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An experiment to understand that the water had not leaked but the process of CONDENSATION had taken place.

Beth could weigh the glass before putting it in the refrigerator for a while to cool it down. Then she could remove it from the refrigerator and allow moisture to collect on the outside. Finally, she would weigh the glass a second time. If water simply leaks from the inside to the outside, the mass of the glass and water will be unchanged. However, if the moisture is condensation, there will be an increase in the mass at the second weighing.

Result

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The reasoning is based on the concept of CONDENSATION.

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Section 13.2: Forces Within Liquids

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