Question

Before Mayer and Joule came along (see Box 7.1), people were well aware that if a person cranked a drill, heat appeared. For instance, the drilling of the bores of cannons was legendary for the heat produced. However, heat per se was believed to be neither created nor destroyed, and thus no one thought that the motion associated with drilling turned into heat. Mayer and Joule go down in history in part because they demonstrated the real relation between motion and heat. Imagine that you were alive in the early nineteenth century, and like Mayer and Joule, you hypothesized that animal motion could tum into heat. Design an experiment that would provide a rigorous test of your hypothesis.

Short answer

The experiment consists of using a horse to pull a weight attached to a pulley system that creates friction and thus heat on a metal block. The changes in thermal energy are recorded over time and compared to the amount of work done by the horse to confirm the hypothesis that animal motion can be converted into heat.

Step-by-step solution

Define the Hypothesis

The experiment starts with the hypothesis: animal motion can be converted into heat. It is based on the law of conservation of energy, which declares that energy cannot be created or destroyed, only transferred or changed in form. Here, the transfer is from kinetic energy (motion) to thermal energy (heat).

Design of the Experiment

Propose an experiment involving an animal performing some physical action, like a horse pulling a weight attached to a pulley system. The pulley system is connected to a friction device, such as a block of metal. The friction generates heat, which could be measured over time.

Implement the Experiment

The horse starts pulling the weight. As the weight moves, it creates friction with the metal block, generating heat. This heat can be recorded over time. The horse's motion or work can be measured in terms of the distance it covers and the weight pulled.

Analysis

Analyze the data for a correlation between the heat produced and the amount of work done (amount of motion). Synchronization between increased motion and increased heat would confirm the hypothesis.

Key concepts

Kinetic Energy

Kinetic energy is the energy that an object possesses due to its motion. It is one of the key components in understanding the conversion of motion into heat energy. The formula for kinetic energy is given by the equation \[ KE = \frac{1}{2}mv^2 \] where \(m\) is the mass of the moving object and \(v\) is its velocity. This means that both the mass and speed of an object determine how much kinetic energy it has.
Kinetic energy is crucial in many everyday situations, such as when you push a shopping cart or when a car travels down the road.
In the context of the nineteenth-century experiment described, the motion of the horse pulling a weight is an application of kinetic energy. Here, the horse's muscular action is converting stored chemical energy into kinetic energy as it moves.

Thermal Energy

Thermal energy, commonly referred to as heat, is the energy that comes from the temperature of matter. It is the result of the movement of tiny particles within the object, also known as atoms and molecules. The faster these particles move, the more heat is generated.
In our daily lives, we encounter thermal energy whenever we notice temperature changes, such as feeling the warmth of the sun or cooking food.
In the experiment designed by Mayer and Joule, the thermal energy is produced when the horse's motion causes friction in the pulley system. This friction rubs surfaces against each other, increasing the internal energy and causing a measurable rise in temperature.

Conservation of Energy

The conservation of energy principle states that energy cannot be created or destroyed, only transferred or transformed from one form to another. This fundamental scientific law explains many natural processes and is essential for understanding energy conversions.
One simple illustration of this is when a ball is thrown into the air. It starts with kinetic energy, which is transferred to potential energy at the peak of its trajectory, and then back to kinetic energy as it falls.
In the given historical experiment with the horse and the pulley, the muscle energy of the horse (chemical energy) transforms into kinetic energy, which is then converted into thermal energy through friction. All forms of energy are accounted for, highlighting the principle of energy conservation.

Experimental Design

Experimental design involves planning a structured method that allows researchers to test a hypothesis or theory under controlled conditions. It includes determining the variables, the process for conducting the experiment, and how data will be gathered and analyzed.
A well-designed experiment is crucial for obtaining reliable and valid results. It should minimize errors and biases and ensure that the results are a true reflection of the hypothesis being tested.
For the historical conversion of motion into heat experiment, key elements of the design include:

• Defining the hypothesis that animal motion can turn into heat.
• Creating a controlled environment where the horse pulls a weight that generates measurable heat through friction.
• Using appropriate instruments to measure the heat produced and the work done.

This structured approach allows for clear analysis and interpretation of results, reinforcing the link between kinetic and thermal energy.