Ideas about Work and Energy What exactly is energy?

Work  We use this word in many different ways….  In physics, Work means something very specific  Work = Force x distance where both Force and distance are vectors.  Work = the amount of Force applied along the direction the object is moving.

Work  Work = Force x distance (mathematically this is the dot product)  Work can be positive or negative.  Positive work increases the energy of an object.  Negative work decreases the energy of an object (think of friction on a sliding object)

Types of energy  There are many types of energy………chemical, nucular, sound, heat, etc.  For now we will mainly be talking about mechanical forms of energy which include Kinetic Energy, Potential Energy, and spring energy  Energy is often described as the ability to do work. It’s a method of keeping track of “stuff” because in a closed system energy is conserved.  Conservation of Energy: one of the main conservation laws in science.

Types of Mechanical energy  Kinetic energy = ½ m v 2. This is the energy an object has because it is moving.  Potential Energy (gravitational) = mgh. This is the energy an object has because it has height and the potential to fall.

Conservative Forces  The Potential Energy of gravity is a “conservative” form of energy.  PE is path independent, it only depends on the starting and ending locations.  PE is always a change in energy, meaning it has a reference point. This reference point is the location you are calling h = 0.

Conservation of Energy  If no external forces are acting, then the total energy of a system does not change.  Examples of this are a 1)pendulum with no friction or air resistance 2) roller coaster with no friction or air resistance.  Can determine speeds and heights based on total energy remaining constant.

Energy problems with work  If an external force is acting, then Work is done by this force.  Work can either increase the starting energy or decrease it.