Mike Tuke’s

SPEED OF COOLING

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Speed of cooling Speed of cooling  D Identical teapots but of different sizes are filled with boiling water. Students are asked to predict which one will cool first and what factors will affect the speed of cooling.  This is good for engendering discussion.   Cooling and crystal size A P F 30 min Use salol to show the relationship between speed of cooling and crystal size. Use a glass rod to put a drop of melted salol at 60oC onto a glass slide at room temperature and put another slide on top and squeeze it down.  Repeat with the other pairs of slides at different temperatures.  The coolest slides give the finest grain size. Cooling and crystal size A G 5 min The class is divided into 4 groups, A, B, C and D and each student is given 16 loose plastic blocks which can be connected to each other. Each block represents a molecule and 2 blocks joined together are a small crystal.  More blocks joined together represent a larger crystal. Students make as many pairs as possible, and then join those to make fours and then eights.  The teacher calls out "group A stop" almost as soon as they have started so they have only molecules (=volcanic glass). Group B is stopped after most blocks are in twos (=fine grained rock).  Those allowed longer produce medium and course grained rock.  I used pieces of "Multilink", which is a construction kit for children . "Leggo "bricks could be used, or even squares of card which are placed beside each other on the desk. Cooling in a liquid  E P F 60 min Two thermometers are placed in a small tin of molten salol, one at the edge and one in the centre. Both thermometers cool rapidly to start with. The rate of cooling slows down and may even reverse as crystallisation takes place because the latent heat of fusion is released. Once the salol is solid the outer one cools much faster than the central one.   Cooling of different sizes using aluminium cans E P 30 min To show how the speed of cooling varies with size, use aluminium cans of different sizes. Pour the boiling water into the cans and record the temperature every minute for 20 min.   Cooling of aluminium shapes E P F 30 min Aluminium blocks of various shapes and sizes are heated to 110oC and their temperature measured as they cool.  The resulting data can be used to show the effect of size, shape, surface area and surrounding temperature on speed of cooling.