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Conservation of Mechanical Energy

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Conservation of Mechanical Energy

Physical Science

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Learners examine the conservation of mechanical energy and learn about lost energy due to friction.

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Now You Know

After completing this tutorial, you will be able to complete the following:

  • Describe total mechanical energy as the combination of potential energy and kinetic energy.
  • Calculate the changes in total mechanical energy when air friction is neglected.
  • Explain the conservation of mechanical energy.
  • Explain the concept of energy lost due to friction.
  • List real-life examples of the conservation of mechanical energy.

Everything You'll Have Covered

The law of conservation of energy states that in an ideal isolated system, where friction is ignored, the total amount of energy of the system will be conserved. However, the energy itself may change from one form to another. In isolated systems typically presented in physics, the total mechanical energy is considered. Mechanical energy is the energy of a body due to its motion or its position. It encompasses both kinetic energy, the energy of motion, and gravitational potential energy, the energy of position in a gravitational field. Mechanical energy is also the type of energy that results from work being done.

The conservation of mechanical energy implies that, as the kinetic energy of a body in an isolated system increases, its gravitational potential energy decreases (and vice versa) so as to keep the total mechanical energy of the system constant. Similarly, as an object's position shifts and its gravitational potential energy changes, the object's kinetic energy must change as well. The kinetic energy (KE) of a body depends on both its mass (m) and its velocity (v), and is expressed by the equation The potential energy (PE) of a body close to Earth's surface depends on its mass, its height (h), and the gravitational acceleration constant Potential energy is expressed by the equation PE = mgh.

When a body falls from a height, h, its velocity continuously increases (because g is an accelerating force) and its potential energy correspondingly decreases (because h decreases). The change in kinetic energy can be determined by subtracting the object's initial kinetic energy from its final kinetic energy. This requires knowing the initial velocity and the final velocity, or the velocities at any two points in the object's path. Although energy is conserved in ideal closed systems, in reality some energy is lost to friction.

Tutorial Details

Approximate Time 20 Minutes
Pre-requisite Concepts Understand energy and work concepts.Understand that energy can be found in different forms, like gravitational potential, electrical, sound, and radiation.Define friction.Explain that potential energy can be converted to kinetic energy, and kinetic energy can be converted to potential energy.Define conservative forces..
Course Physical Science
Type of Tutorial Concept Development
Key Vocabulary conservation of mechanical energy, final velocity, friction