## What happens to water as it cools?

This experiment would have been far, far better if I’d had a thermometer.

My son was doing some science homework, and seemed a bit confused about what would happen to hot and cold water if left on the table.

Now whenever possible, if your child expresses confusion about a science topic, don’t just explain, do an experiment. Most science for young kids is informal enough and practical enough that there’ll be some way to do the experiment around the house.

In this case, it was simple. I filled one cup with water from the kettle, another with water and ice. I asked my son to label each cup, and write down his predictions about what would happen in the end. You can see the setup below:

If we had had a thermometer, I would have asked him to measure the temperature of each cup at various time intervals, say immediately, after 5 minutes, 10 minutes, 20 minutes and an hour. Then he would have been able to see that both cups reach the ambient temperature of the air around them. As it was, his “thermometer” was to dip his finger in the cups. Too subjective, alas. I’ll have to get a thermometer and try again one day.

## Solar Powered Saffron

My solar panels have generated 1500 kWh of energy since they were installed 6 months ago.

Now, Einstein tells us that energy has mass. How heavy is 1500 kWh? We can use E = mc2 to find out.

Here, E is 1500 kWh, the speed of light c is 186000 miles/second. Unfortunately, we can’t just divide 1500 by the square of 186000. Sure, that would give the mass, but not in any unit I’m familiar with – when you tell me how much something weighs, I want to hear it in pounds, or kilograms, or ounces… even centiweight would do, if I have Google handy.