The law of conservation of energy states that it is impossible to create or destroy energy because energy can only be transformed from one form to another or transferred from one body to another (Shipman, Wilson, & Todd, 2009). Therefore, the amount of energy contained in a system remains constant even if some of it is converted to other forms. Kinetic energy is contained in moving bodies while potential energy is contained in motionless bodies. The amount of kinetic energy in a body is affected by environmental factors and the state of surrounding bodies while potential energy is independent of the surroundings (Viegas, 2005). For instance, friction can reduce the amount of energy contained in a moving body because some of the energy is converted to heat energy. In addition, energy is also used to overcome the force of gravity. Several activities explain the concept of energy conversion and transfer from one body to another.
An example of a real-life application that explains the law of conservation of energy is cross-country skiing that involves gravitational force. The skier has to overcome gravitational forces in order to move up the hill. During skiing, kinetic energy is transformed to potential energy and vice versa. When a skier is at the bottom and in motion, kinetic energy is at its maximum. However, as he speeds up the mountain, kinetic energy gradually decreases as the skiing speed reduces. Conversely, the skier’s potential energy increases as the speed decreases. After reaching the top of the hill, potential energy is at its maximum. On the other hand, kinetic energy is zero because of the stationary state. Factors such as gravitational force and friction are also involved in the energy transformation cycle. Kinetic energy is calculated using the following formula. Kinetic energy = ½ mv2 (Shipman et. al, 2009). According to this formula, kinetic energy is half the product of the skier’s mass multiplied by the square of velocity. On the other hand, the product of mass, gravity and height gives potential energy. Therefore, potential energy = m × g × h (Viegas, 2005). According to the law of energy conservation, Ki + Pi =Kf (Viegas, 2005). As the skier speeds down the hill, potential energy is converted to kinetic energy. Kinetic energy increases with increase in speed. Conversely, potential energy decreases with decrease in skiing speed.
Elastic potential energy refers to energy contained in elastic bodies (Viegas, 2005). Examples of elastic bodies include catapults, rubber bands, springs, and bows used to propel arrows. The amount of potential energy depends on the amount of stretch a body undergoes. A real life situation that involves transformation of elastic potential energy is in the use of a dart gun. When using a dart gun, elastic potential energy is converted to kinetic energy. The compressed springs of the dart gun contain elastic potential energy that is transferred to the dart when the trigger is pulled. The springs stretch and transfer potential energy to the dart thus setting it in motion toward the target (Viegas, 2005). The force used to compress the springs is converted to elastic potential energy when the spring is in a compressed state. The aforementioned examples demonstrate the validity of the law of conservation of energy. In the first example, energy undergoes transformation while in the second example involves transfer of energy.
References
Shipman, J., Wilson, J., & Todd, A. (2009). Introduction to Physical Science. New York: Cengage Learning.
Viegas, J. (2005). Kinetic and Potential Energy: Understanding Changes within Physical Systems. New York: The Rosen Publishing Group.