This simple activity models how kinetic energy is transformed into heat or thermal energy on the particle level. Additionally, by comparing data for 3 different metals—aluminum, copper, and lead—students construct a model of heat capacity on the particle level. The data collected can also be used to introduce calculations of heat absorbed or heat lost (Q = mCΔT).
Relate heat to motion in a very simple demonstration. Ask students to quickly rub their hands together for 20 to 30 seconds. On the macroscopic scale, ask them to discuss what happened and why. Then ask if they think the same phenomenon may apply on the microscopic scale.
PE HS-PS3-2. 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 positions of particles (objects).
Ensure that caps are on the vials tightly. Remind students that the vials are glass and will break if dropped. Never use a thermometer to stir.
If class time is short, you may prepare the vials ahead of time with the vial weight and shot weight recorded on the vial. Have students return the vials to a central station. The shot may be returned to storage, or you can store the vials for future classes. No disposal is necessary.
How is shaking the vial like rubbing your hands together?
In both cases particles are moving, colliding, and transferring energy. In both cases the temperature went up.
On the particle level, what made the temperature of the metal shot change?
Shaking the vial transferred kinetic energy to the shot in the vial. Increase in kinetic energy means an increase in temperature.
Everyone shook the metal for the same amount of time. What factors or variables may be affecting the temperature change of the metal? Justify your answer with the class data.
Other factors may include how hard the vial was shaken, if the student stopped shaking during the 5 minutes, the type of metal in the vial, the total mass of metal in the vial.
Using class data, calculate the average mass of the three metals. Compare the average masses.
Student answers will vary.
Using class data, calculate the average temperature change for the three metals.
Student answers will vary.
Are the average temperature changes the same for the three metals? Use data to support your answer. How can this be explained?
Average temperature changes should be slightly different for the three metals. Aluminum has the highest heat capacity, so you would expect it to have the smallest temperature change. Lead has the smallest heat capacity, so it should have the greatest temperature change.
Based on your data and calculations, construct a model that explains the phenomenon of heat capacity, what variables affect the amounts of energy needed to change a substances temperature one degree Celsius.
The model should include mass, temperature change, and the substance. Students may not know to multiply the 3 variables together but that can be discussed.
How do the variables in your model compare to the formula for heat calculations?
Q(J) = m(g) x C(J/g-K) x ΔT(K)
The variables should be the same.
Use the average temperature change and average mass to calculate heat for each metal. Explain any differences in thermal energy among the metals.
Student answers will vary. Check to be certain the final answer is in Joules, the SI unit of energy. Conversion to Kelvin from Celsius is not necessary since calculations are based on changes in temperature. Students should notice that aluminum stores more heat energy before its temperature increases. Lead is just the opposite, it changes temperature with a small amount of energy input.
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