Snow Density

Background:

For many of the experiments being carried out as part of the SIPEX voyage, knowing the density of the snow cover is an important part of the data being collected. This is particularly true for the EM measurements and the radar altimetry teams as their results differ depending on the density of the snow. The way the scientists find snow density is very straight forward and can easily be replicated in the classroom. The simply plunge a cylinder of known diameter and length into the snow and remove a ‘snow core’. Then they weigh the snow that they removed and calculate the density.

Density is defined as mass per unit volume, in other words it’s the mass of a given amount of substance divided by the volume occupied by that amount.

Activity:

This activity can be used to illustrate the concept of density, it allows students to revisit volume and the area of a circle.

Materials:

• Uncooked rice
• Cooked rice
• Film canisters (or some other cylinder)
• Balance
• Card

Procedure:

This activity involves students sampling two different types of ‘snow’ and calculating and comparing their densities.

1. Students are given a cylinder (e.g. a film canister) which they will use to collect a snow sample. They measure the diameter and length of the cylinder and calculate its volume. (Encourage students to make their measurements in metres as this is the SI unit for length).
   
2. Simulate two different types of snow cover by having two large containers, one filled with uncooked rice, and the other filled with cooked rice.
3. Students plunge their cylinders into the snow being careful to stop when the rice reaches the end otherwise the density will be affected.
4. Using a small piece of card students slide it over the open end of the cylinder and remove their snow sample.
5. Students put the snow sample into a small zip-lock bag and weigh their sample on a set of scales. Masses should be expressed in kg.
6. Students calculate the density of the sample using the following equation. The units for density will be kg/m³.
   

Other Ideas:

If students are finding it hard to visualise what is meant by kg/m³, you can get 12 metre sticks and ask students to arrange them to form a cube. This will show them what 1m3 looks like. You can then pass around a 1kg mass (1kg bag of flour would do) and point out to students that X amount of that mass is in a volume of 1m³ for a particular substance (see table below). For example if you take the density of air, just over that 1 lot of that mass is found in every 1m³ of air, whereas for sea water 1030 lots of that mass are found in a m3.

Discussion Questions:

Note: Snow is basically many small ice crystals separated by air. So dry powdery 'light' snow has a low density(~100kg/m³), whereas wet 'heavy' snow has a higher density (~500kg/m³).