Teacher Notes

Topic: Conservation of Energy – Potential energy to Kinetic energy

National Standard Addressed: Conservation of energy and the increase in disorder. Energy can be considered to be either kinetic energy, which is the energy of motion; potential energy, which depends on relative position; or energy contained by a field, such as electromagnetic waves.

Missouri Grade Level expectations addressed by Lesson: Science Strand 1.2B - B. Mechanical energy comes from the motion (kinetic energy) and/or relative position (potential energy) of an object.

Concept Addressed by Lesson:

This lab addresses the principle of conservation of energy which says that in a closed system, energy cannot be created or destroyed but may be changed from one form into another. Potential energy and kinetic energy are used as examples of one form of energy changing into another. Potential Energy (PE) is the energy possessed by an object which has mass by reason of its height position within a force field; in our case, within the force field of gravity. Kinetic energy (KE) is energy possessed by a body which has mass by reason of its motion. whenever an object is raised above the ground all the energy it possesses is potential energy. When released, the potential energy begins to change to kinetic energy as it moves faster and faster. When it hits the ground the PE has been completely converted to KE.

Exploration Activity: The activities involve the use of a toy car to dent an aluminum can. The car is rolled down an inclined plane into the aluminum can, and students observe the dent if any. Students release the car from several different locations on the incline, as well as at different angles of incline and record qualitatively the relationship between release location and damage to the can.

The activities conclude with a station in which the car and can are placed on a horizontal surface. Students are asked to make dents on the can without lifting the car. They are asked to do something that will make a bigger dent. This will range from increasing car speed or loading the car with weights. Students record severity of dents.

Data: Students are to record the severity of the dents for each angle of incline, for the different positions on the incline, weight of car, speed of car. Data will be qualitative in nature, describing dent as Slight, Medium, Severe.

Concept Development: The data would show that the steeper the incline, the faster the car, the farther up the incline the car is, the bigger dent it makes. This introduces energy being transferred to the can, the relationship between potential energy and height, and the relationship between kinetic energy and speed, and the transfer of potential energy into kinetic energy. The principle of conservation of energy is fully discussed at this time. Factors affecting how much a potential energy a body possesses should be discussed at this time viz: mass and height.

Application: Another activity that will apply the above concept is driving nails by dropping weights of different sizes at different speeds on a nail. The higher the weight the better it drives the nail. Also it is easier to drive a nail with a big and heavier hammer than with a lighter and smaller hammer. See student sheet for details. During this discussion example of a wrecking ball in construction should be discussed as a practical application of potential energy.

Materials List:

1. 6 toy cars and carts for 6 groups of 4 students.

2. 6 inclined planes. This could be made out of plank of wood or hard board.

3. 6 Aluminum cans.

4. Weights or rocks of different sizes.

5. Instructions sheet.

Historical Background:

The study of energy, mass and gravity has captivated philosophers and scientists from Aristotle to Galilei Galileo. Galilei was obsessed with disproving Aristotle that he carried out the famous experiment of dropping two balls of different weights from the tower of Pisa, which landed at the same time.

Energy is defined as the capacity to do work. The English physicist and physician Thomas Young (1773-1829) was the first person to use the term energy in this sense. The concept of energy unites almost all branches of science through its various manifestations (light, heat, atomic and subatomic behavior, etc.). Energy can be converted from one form to another and the total energy in any closed system remains constant. In classical physics, this principle was known as conservation of energy; in modern physics, it is termed the conservation of mass and energy. The doctrine of the Conservation of Energy was long preceded by that of the Constancy of Matter. This was held vaguely as a metaphysical postulate by the ancient materialists and positively formulated as a philosophical principle by Telesius, Galileo and Francis Bacon. Descartes assumed in a somewhat similar a priori fashion that the total amount of motion (MV) in the universe is fixed–certam tamen et determinatam habet quantitatem (Princip. Philos., II, 36). But the effort to establish such assumptions by accurate experiment begins later. According to many we have the principle of the conservation of energy virtually formulated for the first time in Newton's Scholion developing his third law of motion (action and reaction are equal and opposite)

References:

Zollman, Dean (1990). Learning Cycles for a Large Enrollment Class. Physics Teacher, 28, 20-25(1990).

Marek, A. E., Methven, B.S., (1991). Effects of The Learning Cycle upon Student and classroom Teacher performance. Journal of Research in Science Teaching, 28, 41-53.

http://www.bookrags.com/sciences/physics/conservation-of-energy-wop.html

http://www.newadvent.org/cathen/05422a.htm

http://jersey.uoregon.edu/vlab/PotentialEnergy/