Abstract
How does the comparative density of ice and water affect water levels as ice melts in different circumstances? This article attempts to demonstrate this.
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1. Experiment 1: Melting ice
The first cylinder is simply solid frozen coloured water, whereas the second cylinder contains water with a floating cylinder of ice. So, some ice protrudes above the surface of the water (as seen in figure 1).
Figure 1. Showing set up with ice in cylinders.
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Standard image High-resolution imageWhat will happen to the water levels when both ice cylinders fully melt?
2. Experiment 2
The second experiment consists of water and ice in two drinking glasses. The first shows some ice which has sunk because frozen into the ice are four pound coins, so that the overall density is greater than the density of tap water (figure 2). The second beaker (figure 3) shows pure tap water ice floating in an almost saturated solution of salt. This ice clearly floats higher in the salt than it would in tap water, because of the increased density of the brine.
Figure 2. Ice blocks containing coins to increase the average density.
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Figure 3. Tap water ice floating in a concentrated salt solution.
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Standard image High-resolution imageThe level of the contents is marked in each case, we will return to this beaker once all the ice is melted. Will any of the water levels change, even by a small amount, or will some stay the same?
3. Experiment 3: On land or in the sea
In this experiment we have attempted to compare the runoff of ice melt from land (as in the Antarctic or land surrounding the Arctic Ocean) with the melting of floating ice (as at the North Pole). The set up is shown in figure 4.
Figure 4. Two 'paint trays' containing water with the ice block on the left floating and the ice block on the right resting on an artificial island.
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Two paint trays are used, with the deep part filled to the brim with water and the simulated nearby (lego) land on the sloped section. One has ice floating whereas the other has a similar block of ice resting on an island in the water. The water levels are adjusted to be just at the edge of the sloped green lego surface. Will there be a difference once the ice melts?
Other questions to consider are how closely does this represent what is happening at the poles due to global warming? How could we make the representation more realistic?
Biographies
David Featonby taught in a large comprehensive school in Newcastle for many years and since retiring worked as a Teacher Network Coordinator for IOP, and latterly as a member of the Executive Board of Science on Stage Europe. He has presented workshops throughout the UK and Europe, and provided articles for this series of "What Happens Next?" experiments for Physics Education, continuously since 2010. Most recently during the pandemic he has provided teachers with a daily "What Happens Next?" video on Facebook, with over 130 experiments during 2020 and 2021, and provided on line workshops and webinars for Science on Stage on topics including "Magic - Science we don't see".