Chapter 13: Work and Energy Section 3: What is energy?

Energy and work Whenever work is done, energy is transformed or is transferred from one system to another system Definition of energy: The ability to do work Energy comes in many forms: Nuclear Chemical Mechanical Heat Sound Energy is measured in Joules (J)… just like work! The ones we are talking about in physical science.

Types of Mechanical Energy POTENTIAL ENERGY Kinetic energy The energy that an object has because of the position, shape, or condition of the object. Two types: Elastic potential energy Gravitational potential energy The energy that an object has due to the object’s motion 𝐾𝐸= 1 2 𝑚 𝑣 2 𝑃𝐸 𝑔 =𝑚𝑔ℎ Total mechanical energy = PE + KE

More about Potential Energy Sometimes this type of energy is referred to as Stored energy Elastic potential energy depends on how stretched or compressed the object is Gravitational potential energy depends on The mass of the object The relative height Relative to where the reference point is defined

More about kinetic energy Kinetic energy depends on The mass of the object How fast the object is moving Because velocity is squared, KE depends on speed more than mass Atoms and molecules have kinetic energy, because they are always moving.

Other forms of energy Chemical reactions involve potential energy Photosynthesis is the process that turns energy from the sun into chemical energy that is stored in sugars and other molecules in cells When you eat, you are eating stored energy… potential energy The sun gets energy from nuclear reactions, called nuclear fusion Energy can be stored in fields Earth’s gravitational field stores gravitational potential energy Electric fields store electrical energy