For each group:
For each student:
Particles that make up substances are always moving and always have energy. This energy can be transferred from one object to another by three means—conduction, convection, and radiation.
There is a difference between heat and temperature. Heat is the energy that the object has because the particles are moving. Temperature is a way of measuring heat energy. Two scales that are commonly used to measure heat are the metric system and the standard system. The metric system uses Celsius(ºC), and the standard system uses Fahrenheit (ºF) to measure heat. The measurement of temperature gives the average amount of energy contained in the substance.
Heat always travels from hotter to cooler objects. It may seem that when you are holding an ice cube, the ice cube is causing your hand to feel colder. However, the real physics behind this heat transference is: The feeling of coldness in your hand is caused by the heat flowing away from your hand and into the ice cube. REPEAT: Energy from the faster moving (hotter) particles transfer to the slower (colder) particles. The transfer of energy goes on until all the particles in both objects are moving at about the same speed. When the amount of heat energy of each object is the same, both objects will have the same temperature.
When two objects come into contact with each other, heat energy moves between them because the particles in one object collide with, or 'bing,' the particles in the other object. Transferred heat resulting from the collision of particles is called conduction. Conduction works best through solids, especially through materials such as metals. An example includes observing a raw egg fry as it hits a heated frying pan.
Heat energy transferred by the movement of a liquid or gas is called convection. When particles are heated, they move faster, expand, become less dense, and ‘bang,’ the particles rise. As the liquid or gas cools, the particles move slower, contract, become more dense, and ‘bang,’ the particles sink. This movement of heating, expanding, rising, cooling, contracting, and sinking is a continuous one. An example is to observe the amount of wind in the early morning compared to the afternoon. Wind is an example of a convection process in motion.
Conduction and convection need a medium to transfer heat energy; however, radiation does not.Radiation uses electromagnetic waves such as ultraviolet, visible, infrared, and microwaves, ‘boom.’ These invisible waves carry energy through empty space, as well as through solids, liquids, and gases. All objects give off electromagnetic radiation, which means warm objects emit more radiation than cool objects. An example is the radiation from a campfire making you feel warm as you roast marshmallows.
Set up a microwave oven in front of the classroom and pop a bag of popcorn. Ask students several questions relating to what’s going on inside the microwave oven.
- What type of energy is a microwave using?
- Why does it pop popcorn? Where did the energy come from?
- Why does the bag feel hot when you first pull it out?
- Why should you wait a few minutes before eating the popcorn?
- Where did the steam vapors come from?
- Feel the air just above the bag as you open it. Why is it warmer than the surrounding air?
During this discussion, list student ideas on chart paper. Revisit this list at the end of the heat unit.
Activity #1—‘BING’—Melting Ice Using Conduction
Activity Time: 20 minutes
- This is a short demonstration with room temperature water and ice. Using a thermometer, take the temperature of a glass of room temperature water. Add several ice cubes to it and let set for a few minutes. Take the temperature of the water after having ice added to it. Have a short discussion about the following question: When you add ice to warm water, does the warm water melt the ice or does the ice make the water colder?
- Explain to students that they are going to see who can melt an ice cube the fastest using only their hands.
- Give a container to each group of students filled with enough ice cubes for every student to have his/her own.
Option: Place each ice cube in a Ziploc bag.
- Explain to students that they will all begin at the same time.
- Give the signal to begin.
- After the initial mayhem and students are complaining about their hands freezing, ask students why their hands are so cold? Ask if the ice made their hands cold or did the heat from their hands cause the ice to melt? Ask how this experience relates back to the initial question about the ice and water.
- Ask students what would eventually happen to the temperature of the ice water if left alone for 24 hours.
Answer the questions to this assignment in a Word file. Save the file in the appropriate place on the network. Then, upload the completed file to this assignment link by clicking the Submit Assignment button in the upper right hand corner of this window. Proofread your work carefully before you submit it.
Lesson copied from http://www.uen.org/Lessonplan/preview?LPid=11545 on December 12, 2014.