Energy Flow (John Kennedy)

Title: Melting Ice Blocks

Principle(s) Investigated: Energy Transfer, Thermal Conductivity, Heat Transfer

Standards: HSPS3-2: Develop and use models to illustrate that energy at the macroscopic scale can be accounted for as a combination of energy associated with the motions of particles (objects) and energy associated with the relative position of particles (objects).

Materials: Ice, IR Thermometer, Two different Block Materials (Do not have to be the black blocks)

Procedure:

1. Have students determine the identity of the two different tile materials and record it.

2. Predict a value for the temperature of each tile. Estimate and write down your prediction

3. Draw a simple model to show what the particles may look like in each tile.

4. Use an IR thermometer to test the temperature of each. Do your initial predictions match the recorded temperature? Revise your model if necessary to reflect new data, use a different color if able too.

5. We are going to put a piece of ice on to each tile. Predict which one will melt the ice more quickly. Write down your prediction. If you think they will melt at the same time, indicate that as well.

6. On your model, draw the ice and show how the particles in the ice and the block interact. Your model should support your prediction.

7. Place an ice cube on each tile and record the time it takes for it to melt.

8. Do your initial predictions match up with the actual melting rates? If needed, revise your model to better reflect the data.

9. Collaborate with the groups next to you. Use any constructive feedback to edit your model.

10. Write a few sentences to describe what is happening in your model and explain why the ice melted more quickly on one tile than the other. Take a photo of your model and response and upload via the form.

Student prior knowledge: What prior concepts do students need to understand this activity?

Students should know that ice melts at 0 C

Energy must be supplied in some way to make the ice melt. Concept of transfer of energy from high to low

How energy is transferred through conductivity.

Explanation:

There are two discrepant events that are occurring here.

First is that objects of the same temperature can feel as if they are different and the second being that they can melt ice at different rates.

To melt the ice, energy has to be supplied to the ice. The average temperature in a room is about 20 C whereas the ice is going to be 0 C. For the ice to melt, the energy in the classroom needs to be transferred. In this experiment, there are two different materials that the ice is in contact with; a high-density foam block and a metallic (Aluminum) block. Metal is a better conductor than plastic, foam, and wood so energy is transferred more quickly through it to the ice.

When your skin comes into contact with the metal block, because it is an excellent thermal conductor, it removes heat from the surface of your skin which sends a signal to your body that the object is cold. Because of this signal to the brain, objects that are good thermal conductors give the misconception that they are colder than thermal insulators when they are both at the same temperature.

Questions & Answers: Give three thought-provoking questions and provide detailed answers.

1. Ice melts more quickly on the metal block than the plastic/foam one. Would the results be different if ice cubes were placed in a metal and plastic box so they would be fully enclosed?

The results would still be the same regardless of the ice being in a closed container because the thermal conductivity of the metal does not change. This would be different if there were a second wall and form of insulation between the two boxes.

2. Because Thanksgiving is right around the corner, As Seen On TV is airing an ad for an amazing rapid defroster that will cut the wait time for your turkey to defrost. Could you simply use a cookie sheet to achieve the same result without paying for an overpriced item plus shipping and handling?

At first, it may seem like a good solution to simply place your turkey or frozen item on a cookie sheet, however, most cookie sheets have a thin space between the top and bottom of the sheet to prevent burning the bottom of your food. If you are a hands-on DIY person, you could go to a local hardware store to buy a solid metal sheet and may your own defroster plate.

3. Using the data from this experiment consider the following scenario: on a hot day, should use take a cold shower or a warm shower to cool your body down?

While it seems tempting to jump into a cold shower to cool off on a hot day, it will actually not do an effective job at cool you down. Heat transfers from high to low and just like the metallic block, cold water would remove thermal energy from your skin's surface. Your body transfers heat from itself to the water so it seems like cold water would be the optimal choice. The catch here is the signal of that "cold" you get when you come into contact with the water effects how your body respond. Your body reacts to feeling cold and instead of cooling down, your body will try to retain its heat. To cool down during the summer, you would want to take a warm shower to prevent signaling you are cold but rather you are warm. When you do this, your body begins to take actions to shed its internal temperature which in turn cools you off.

Applications to Everyday Life:

Hydroflask: Insulated water bottles do an incredible job of keeping drinks cold for several hours. This is done by using a double walled system with a vacuum inside. While metal is a great thermal conductor, the vacuum prevents the flow of energy keeping the inside cold. A common noise to many hydroflask owners is when one drops. Many times you walk away with a dent but the vacuum seal is intact. Other times, while there is no sign of cracks, a dent may deep enough to touch the inner wall and this creates a pathway for energy transfer and will prevent your bottle from keeping a cold temperature.

Circle K Fountain Drinks "Stays Cold Longer": While crushed ice plays a roll in keeping your beverage cold using more surface area of ice, the reason why your polar pops and soda stays colder longer than most other gas stations/fast food cups is the use of styrofoam. Styrofoam has a lower thermal conductivity than plastic or cardboard cups which keeps your drink colder while you are stuck in traffic on the 405 freeway.

Heat Sinks: May electronics use heat sinks to pull heat away from critical and sensitive components. They provide a large surface area for airflow to pass over the metal to transfer heat away and regulate temperature for a system.

Videos: Include a video of your investigation