Heat transfer experiments can be exciting and engaging. Heat Energy is often called thermal energy. Thermal energy is present in the molecules of an object. When an object is hot the molecules have a lot of energy and move fast. When an object is cold, the molecules have little energy and move slowly.
Thermal energy transfer involves the transfer of internal energy. The three types of thermal energy transfer are:
Conduction involves direct contact of atoms, convection involves the movement of warm particles and radiation involves the movement of electromagnetic waves.
The Second Law of Thermodynamics states that heat will always move from a hot object to a cooler one. Heat transfer is the movement of thermal energy as it transfers from one object to another or between an object and its surroundings. Thermal energy will naturally work towards a state of balance or equilibrium. This is known as thermal equilibrium, where two objects or an object and its surroundings achieve the same level of heat energy (thermal energy).
The Bottle Crush experiment below is a fantastic fun way to demonstrate this principle.
Bottle Crush Experiment
This lesson demonstrates the relationships between temperature, volume, and pressure. Students use water with different temperatures to physically change a plastic bottle. The lesson can be extended to address energy and energy transfer.
- Empty 2 litre plastic bottle with lid
- 6-8 cups of Ice
- 1/2 cup Boiling Water
- 8×11 pan
- Pitcher of Ice Water
Step 1 – Fill the 8×11 pan with ice.
Step 2 – Run the empty pop bottle, with the cap off, under hot water for a minute.
Step 3 – Then put on the cap and place the bottle in a pan of iced water
Step 4 – Slowly pour the pitcher of ice water onto the bottle.
Step 5 – Stand the bottle up and observe what happens. The plastic bottle has been crushed in.
How Does the Experiment Work?
Once the hot boiling water was placed in the bottle, it heated up the air inside the bottle. When we put the cap on the bottle, the hot air was trapped inside.
When we then placed the bottle in the ice and poured the cold water on it, the air inside the bottle began to cool down. Cool air exerts less pressure than hot air, therefore the air pressure inside the bottle begins to decrease.
The air pressure inside the bottle decreased to the point where it was less than the air pressure outside the bottle. Therefore the pushing in was greater than the pressure pushing out, causing the bottle to be crushed.
Coloured Coffee Cups Experiment
Here’s another fun and easy experiment, the Coloured Coffee Cups. This experiment demonstrates radiation. For this you will just need two white coffee cups with one painted matt black on the outside, hot water, two insulating lids with holes for thermometers and stirrers, thermometers and a darkened room.
- Run hot water from a tap for a minute or two, until it reaches its maximum temperature.
- Fill the cups with hot water and put in the stirrer and then cover each with its lid and move them to a dark, cool room.
- Place a thermometer in each one and wait 20 minutes.
- Stir the water in each cup and read each thermometer in each cup and compare the temperatures for each colour.
The darkest colour should read the coolest because, just as they are better at absorbing heat energy, they also radiate heat energy more efficiently than lighter colours.
Colourful Convection Currents Experiment
For our third experiment suggestion let’s take a look at invisible convection currents with our Colourful Convection Currents experiment.
- 2 Bottles
- Blue and Yellow food colouring
- A Playing card
- Masking Tape
- Marker Pen
Step 1 – Fill two of the bottles with hot water from the tap and the other two bottles with cold water. Use masking tape and a pen to label the bottles “HOT” and “COLD.”
Step 2 – Use yellow food colouring in the warm water and blue food colouring in the cold water. Each bottle must be filled to the brim with water.
Step 3 – Your first observation will be what happens when the bottle filled with hot water sits on top of the bottle filled with cold water. To do this, place the card over the mouth of a hot water bottle (the yellow water). This can be a little tricky, but with practice you’ll get it. Useful tip: (practice doing this with two bottles of ordinary water before trying the coloured one) Hold the card in place as you turn the bottle upside down and place it on top of a cold-water bottle (the blue water). The two bottles should be positioned so that they are mouth-to-mouth with the card separating the two liquids.
Step 4- Carefully slide the card out from between the two bottles. Make sure you are holding the top bottle as you remove the card. Watch what happens to the coloured liquids in the two bottles with the card removed.
Step 5 – The second part of the experiment is similar to the first. This time, you need to place the cold water (blue) on top of the hot water (yellow). Repeat Steps 3 and 4 and carefully remove the card. Watch what happens this time.
Hot air balloons rise because warm air in a balloon is lighter and less dense than cold air. Similarly, warm water is lighter or less dense than cold water. When the bottle of warm water is placed on top of the cold water, the more dense cold water stays in the bottom bottle and the less dense warm water is confined to the top bottle. However, when the cold water bottle sits on top of the warm water bottle, the less dense warm water rises into the top bottle and the cold water sinks into the bottom bottle. The movement of the water is clearly seen as the yellow and blue food colouring’s mix, creating a green liquid. The movement of the warm and cold water inside the bottles is referred to as a convection current.
Lascells and Energy
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