## DrDAQ

#### Data logger, oscilloscope, signal generator and more!

DrDAQ is a versatile instrument that connects to the USB port of any PC. Using the supplied PicoScope software it can be used as an oscilloscope, spectrum analyzer and signal generator.

# Which freezes quicker, hot or cold water? results

The experiment was run with the two samples being frozen at different times. This enabled us to use a large container and keep the the container, freezer and volume of liquid a constant.

Figure 1: the freezing curve of water at room temperature

Figure 2: the freezing curve of water at 40 °C

To properly compare the results from the two traces we exported the data to a spreadsheet program. This allowed us to overlay the two sets of data on the one graph. If you measured the data from two samples at the same time you would be able to see this result instantly in PicoLog.

Figure 3: both sets of results

The results from the graph above shows that hot water sample reaches the 0 °C freezing point sooner that the water sample at room temperature: this is known as the Mpemba Effect.

## Discussion of results

The Mpemba Effect was first discovered by a Tanzanian student while making ice cream in 1969. The Mpemba Effect is the phenomenon whereby hot water can, under certain conditions, freeze faster than cold water.

Scientists have identified a number of factors to explain the Mpemba effect (conduction, evaporation and convection) but so far all the theories are only speculative.

Conduction — this effect is more suitable when water samples are cooled in a freezer. When the sample containing the hotter water is placed on a shelf, in the freezer, the heat will melt the ice under the container. When this re-freezes there will be a better conductor of the heat away from the container than the sample of cold water just sitting on the shelf.

Evaporation — this is important if the temperature of the water sample is high and the container has a large exposed surface area. Evaporation has the effect of removing mass from a high temperature sample, which will then compensate for the greater temperature range.

Convection — water is at its most dense at 4 °C. If a water sample starting at 4 °C is placed in a freezer the water at the surface will cool rapidly. Because the water at the surface is less dense that the water beneath the frozen layer will stay at the surface and form a insulating layer for the water beneath.

The hotter sample will behave differently. The water at the surface will cool rapidly due to evaporation, and will become denser that the hot water below. The denser surface water will then sink to the bottom of the container and push the hotter water to the surface. The process is then repeated and this circulation of water causes a rapid drop in the water temperature.

## Teachers' notes

### Safety issues

Students should be careful to avoid burns from both the hot and frozen water.

### Time

This experiment requires several hours to complete.

### General notes

This experiment demonstrates the Mpemba Effect. The Mpemba Effect is where the same quantities of hot and cold water are cooled together and it is found that the hot water reaches zero Celsius first. An interesting investigation in which the reasons for it are still debated.

Target age groups:
Ages 14-19

National curriculum:
Science Key Stages: 4 and 5

## Testimonials

• The kit (2408B) is of obvious quality, easy to setup and calibrate and the free to download software has a reasonable learning curve. Superb kit, superb support, what more can I say.

Rop Honnor
• I have been using my 4224 PicoScope for years. I travel abroad so this has been ideal due to its physical size. Storage of waveforms on my Laptop is very easy allowing me to quickly email waveforms to my Colleagues.

Andrew
• Not many USB scopes works on Win & Mac & Linux too, so that proves me that guys from Pico really cares about us, customers. This made my decision much easier when I was looking to buy an USB scope.

Raul Trifan
• We have been using Picoscope 6404D for quite some time, and are amazed by its accuracy and powerful emulations while working with numerous signal evaluations.

J Mohanty
• PicoLog TC-08: This is a very nice unit that works consistently and reliably.

Jeff Hulett
• It is a great scope. I had a weird problem - it did not work on one of my PC’s. Customer service gave me first class service. If I could give 6 stars for customer service - I would do so.

Niels Larsen
• Perfect Partner for Development of Encoder controlled Stepper Motor Actuators. Since the included software is really stable, this type of device is a great tool for great tasks!

Helmut Schoettner
• A superb piece of equipment worth its weight in gold

Nigel Clinch
• So simple to use & beats any other I have ever used hands down.

John D Samsing
• Rather than webcam our benchtop scope screen, it was suggested we use a PicoScope to share waveforms via screen share.

We were a bit hesitant at first … but it worked flawlessly, and everybody is now out shopping for PicoScopes!

T Lövskog • SVP of Innovation at Additude AB
• Great functionality in a compact size. I really like moving the mouse pointer to a position and having the Time and Voltage display the values at that point. Calibration equipment is a breeze with that feature.

Don Horein

PC oscilloscope and data logger products