University of Virginia
Physics Department

## Heat Conduction

A Physical Science Activity

2003 Virginia SOLs

• PS.1
• PS.7

Objectives

Students will

• understand the process of heat transfer through conduction;
• determine properties that affect the thermal conductivity of a material;
• experimentally test the thermal conductivity of various substances.

Motivation for Learning

Driving Question

If you were stirring a pot of spaghetti in boiling water in the kitchen, would you rather use a wooden or metallic spoon? Why? Why are kitchen items such as teapots and pans usually made of metal? Discuss other examples of good and poor heat (thermal) conductors in the home.

Background Information

Thermal energy is required in many different aspects of our lives. Heating systems and refrigeration both rely on this type of energy to function; they function by adding or removing thermal energy from an object or area to control its temperature. This transfer of energy can occur by three methods: conduction, convection or radiation. Conduction is the most direct transfer of energy, as it requires two objects to directly contact one another. Thermal energy moves from particle to particle throughout a material as heat is conducted.

Conduction takes place when water heats on a stove top, or when a person takes a warm bath, or when a hot pan is cooled by running it under cold water. The mechanism of conduction is simple. As the temperature of a substance increases, so does the kinetic energy of its individual particles, which causes them to resonate rapidly within that substance. These high energy particles then collide with those at a lower temperature, transferring energy through the substance. For example, if a metallic spoon were placed in hot water, initially only the particles in contact with the water would increase in thermal energy. The energy would then propagate through the spoon until heat was felt at its handle.

Some materials are naturally good conductors of heat, while others are poor. Metals usually conduct heat extremely well, which explains the use of iron and copper in cooking utensils. Materials such as plastic, glass or wood do not conduct well; therefore, it is a better idea to use a wooden spoon than a metal spoon when cooking.

In this experiment, students will explore conduction through two examples. The first will compare the conductive capabilities of copper and cork. They should find copper, a metal, to conduct heat much faster than the cork. The second example will test the conductivity of three kitchen utensils made of plastic, wood and metal. They are asked to determine which utensil heats the quickest. Metal conducts heat at least 500 times better than wood. The relation between heat conductivities for wood and plastic depends on the type of plastic, but the values are similar. Use the driving question to explore other examples of good and poor heat conductors used in everyday life.

### Student Activity

Materials

 19 cm long, stiff copper wire Metal spoon 2 small corks 3 quarters Matches 600 mL beaker Candle 300 mL water Wooden spoon Hot plate Plastic spoon

Procedure

Part I:

1. Cut the copper wire into 3 pieces: one piece 10 cm long and two pieces 4.5 cm long.
2. Push the longer copper piece through the middle of one cork so that the cork is at its midpoint. BE VERY CAREFUL DOING THIS!!
3. Push the smaller pieces into either end of the second cork, but not touching inside.
4. Light the candle or burner.
5. Each partner should hold the end of one wire in the flame (See diagram).
6. Note the approximate time until the heat can be felt on the opposite end of the wires. As soon as the wire feels warm, remove it from the flame.
7. Record which wire heated faster.

Part II:

1. Press a small piece of warm candle wax from Part I into the handle of each of the three spoons (see diagram). Push the quarters into the wax so that they are attached to the spoons.
2. Fill the beaker with 300 mL water and place the beaker on a hot plate.
3. Place the three spoons in the water so that the quarters come out of the top of the beaker.
4. Turn on the hot plate and allow the water to warm. Observe the quarters and note the order in which they fall from the spoons.

Data Sheet

 Part I: 1. In which wire was heat felt first? How much of a difference was there in the time it took the two wires to heat?     2. Explain the difference in the rate of heating of the two wires.     3. From your observations, do you think cork or copper is a better conductor? What properties make one material more conductive than the other?     Part II: 1. In what order did the quarters fall from the spoons? Explain this based on heat conductivity.     2. Identify and explain a kitchen item made of each plastic, metal and wood. Distinguish the uses of these items based on heat conductivity.     3. Explain energy transfer through heat conductivity in your own words.

Students with Special Needs

All students should be able to participate in this activity.

Click here for further information on laboratories with students with special needs.

Assessment

Data sheet to be completed during the laboratory.