Physics (9-1) - 0972 CIE

Density

Overview

Lead is called heavy and cork is called light, yet a tiny lead pellet weighs far less than a whole cork life-ring. What we really mean is that lead packs much more mass into each unit of volume. That idea, mass per unit volume, is density, and it lets you predict whether a pebble sinks, why an iron ship floats, and which liquid settles on top when two will not mix.

In this lesson you will define density, learn the equation that links mass, volume and density, and measure it for a liquid, a regular solid and an awkward irregular solid using displacement. You will then use density data the way examiners ask: to decide whether an object floats or sinks, and whether one liquid floats on another.

Objectives

Define density as mass per unit volume; recall and use the equation m ρ = V
Describe how to determine the density of a liquid, of a regularly shaped solid and of an irregularly shaped solid which sinks in a liquid (volume by displacement), including appropriate calculations
Determine whether an object floats based on density data
[Supplement] Determine whether one liquid will float on another liquid based on density data given that the liquids do not mix

Lesson Note

Engineers work out the weight of a bridge from the volumes and densities of its materials before a single beam is cut. A diver chooses weights so their average density matches the water. A cook knows oil floats on vinegar. All of these are density at work, and in the exam density is one of the most reliable sources of marks because the equation is short and the reasoning about floating is logical, not memorised.

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Lesson Evaluation

Congratulations on completing the lesson on Density. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.

You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.

Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.

Density is defined as A. mass times volume B. mass divided by volume C. volume divided by mass D. weight divided by area Answer: B
A block has mass 240 g and volume 30 cm3. Its density is A. 0.125 g/cm3 B. 8 g/cm3 C. 80 g/cm3 D. 7200 g/cm3 Answer: B
A stone of mass 75 g raises the water in a measuring cylinder from 40 cm3 to 65 cm3. Its density is A. 1.15 g/cm3 B. 3.0 g/cm3 C. 1.88 g/cm3 D. 25 g/cm3 Answer: B
An object will float in a liquid if the object's density is A. greater than the liquid's density B. equal to its own weight C. less than the liquid's density D. equal to the liquid's mass Answer: C
The density of water is 1.0 g/cm3. In kg/m3 this is A. 0.001 B. 1 C. 100 D. 1000 Answer: D