Fields: Forces and Energy Objective 2: Describe what a field is, how it relates to non-contact forces, and how it relates to energy.

Forces as Vectors A vector is a value that has both magnitude (size) and direction. Usually a vector is drawn as an arrow. Vectors are often used to represent the size and direction of a force acting on an object.

Vector Field A vector field is a map of all vectors over a space or area, as shown here Vector fields can be used to model many things that we can observe: ocean currents weather patterns and most importantly, non-contact forces!!

Fields For non-contact forces (when objects do not touch), a field is the space around an object where the force exists. Example: The Earth has a gravitational field where other objects experience the pull from the Earth’s gravity Fields never disappear, no matter how far away from the object you are!

Examples – Vector Force Fields Gravitational Fields Gravitational field lines show which way an object within the field will move. Gravitational field lines on the surface of earth pull masses straight down. Gravitational field lines in space pull masses towards the earth (which is still straight down).

Examples – Vector Force Fields Electric Fields Electric field lines show which way a positive charge within the field will move. Positive charges push other positive charges away (arrows point outward); negative charges pull positive charges in (arrows point inward). Electric field lines also show which pairs of charges will attract (top) or repel (bottom).

Fields & Energy Vector force fields store potential energy. We know this because objects released within the field will start to move! Objects released in the Earth’s gravitational field will fall. Because these objects had gravitational potential energy! Charges released in an electric field will move towards or away from each other, depending on their charge (positive or negative). Because these objects had electric potential energy!

Maximizing Potential Energy An object has MORE potential energy when it has farther distance it could potentially travel. When an object is released within a field and it begins to move, its potential energy decreases. The higher up an object is lifted into the air, the more gravitational potential energy it has. The amount of gravitational potential energy it has decreases as it falls towards the Earth.