Sunday, March 21, 2010

The Principle of Convection

In Science, we are using the FANTASTIC (and FREE) EnergyWorks Student Guide created by The NEED (National Energy Education Development) Project. Clicking on the link will take you straight to the pdf to download it. It's 80 pages of information and science projects on Heat, Light, Motion, Sound, Growth, and Electricity/Technology.

Last week we studied Heat and the favorite science experiment by far was Heat 6, exploring the principle of convection. Heat travels through solids by conduction, through liquids and gasses by convection. Convection means that warm rises and cool sinks. In the summer your attic is the hottest part of the house and your basement is the coolest. Convection is what creates currents in water. It is also what creates wind. (As the light from the sun beats down on our planet, the earth soaks up more than the oceans do. The warm air over the soil rises and the cooler air over the water swoops over to take its place. This swooping air is wind.)

To do this experiment, you will need

A pitcher of ice cold water
A pitcher of hot water
A clear plastic bowl
Two clear plastic cups
4 glass marbles
An eyedropper
Calligraphy ink

We modified the activity slightly and included a portion where the ink is dropped in just cold water first. This gave students a previous experience for purposes of comparison, and to help them more clearly see how currents in the water formed when heat was added to the system.

First, fill the clear plastic bowl with ice water. Without disturbing the surface, place the eyedropper close to the water without touching it and carefully drop one drop of calligraphy ink onto the water. Observe.

Next, place four glass marbles in the bottom of one of the plastic cups. Pour hot water into the cup until it just covers the marbles. Place the second plastic cup inside the first, so that it is resting on the marbles. Fill this cup almost to the top with the ice water. Wait 15 seconds. Add a drop of ink as before. Observe.

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