Why Ice Floats
Written by Studio AM.
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Drop a stone into water and it sinks. Place an ice cube in water and it floats. The reason is density: ice has less mass packed into each bit of space than liquid water does.
As water freezes, its molecules join in an open pattern with small gaps. The same amount of water takes up more room as ice. Because it is less dense than the liquid around it, the ice stays on top.
This matters in a lake. On a cold day, ice forms at the surface instead of dropping to the bottom. The floating sheet acts like a lid and slows the loss of heat. Water can remain liquid beneath it, giving fish, frogs, and other organisms a winter habitat.
If ice were denser than liquid water, new ice would sink. More water at the surface could then freeze and sink too. A lake might freeze much more deeply. The floating lid does not protect every lake in every condition, but its position at the top often leaves living space below.
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Questions
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Question 1 of 4
What is the passage mainly about?
The answer is B: Why ice floats and helps water beneath it stay liquid
The passage explains the density of ice, then shows how floating ice can protect liquid water below.
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Question 2 of 4
What does a floating sheet of ice do?
The answer is C: It slows heat loss from the water below
The third paragraph says the sheet acts like a lid and slows the loss of heat.
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Question 3 of 4
A fish is swimming below a lake's ice. What can you conclude?
The answer is D: A frozen surface does not mean all the water below is frozen.
Floating ice slows heat loss, so liquid water can remain below a frozen surface. The fish's presence does not tell us the air temperature.
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Question 4 of 4
In this passage, “density” describes
The answer is A: how much mass is packed into an amount of space
The first paragraph defines density as how much mass is packed into each bit of space.
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