The thermometer uses the fact that most things expand as they warm up and contract when they cool down.If you raise the temperature of a gas, the particles that make up the gas absorb heat energy and begin to move faster. This causes the gas to expand
Half fill the bottle with water and add a few drops of food colouring. You may need to add more water depending on the size of your bottle and length of your straw.
Place the bottom of a straw in the bottle so it touches the water. The top of the straw should be sitting well above the mouth of the bottle.
Holding the straw in place, tightly seal around the straw and the top of the bottle with plasticine. Be careful not to crush the straw.
Blow a little air through the straw into the bottle so that the coloured water to rises up into the straw above the stopper. Be careful when you blow into the straw. If you blow too much air into the bottle a jet of water will squirt back at you.
If the water level in the straw drops, it means air is escaping through the seal. You need to make sure you have no leaks in your seal..
When there is water in the straw you may need to remove any air bubbles inside the straw by moving a skewer up and down in the straw. What happens to the .water level in the straw?You may need to use an eye-dropper to add water to the straw so the water level is about five centimetres above the top of the bottle.
Mark the level of the water in the straw with a pen.
You have now calibrated your thermometer to room temperature.
Cup your hands around the bottle or place it near something warm in the room. Be careful not to place plastic too close to a heat source or it will melt. What do Place the bottle in the fridge and after about ten minutes take it out and look at the water level in the straw
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