Dynamics

12A Classifying Forces

• Force

  • Force: a push or pull on an object

  • Dynamics: the branch of physics that studies forces and how they can change an object’s motion

  • Contact Force: a force that acts only when one object touches another

  • Field Force: a force that acts between objects that are not touching; also called force at a distance

  • Balanced Forces: simultaneous forces whose pushes and pulls cancel each other out

  • Net Force: the vector sum of all the forces acting on an object

  • Unbalanced Forces: a collection of forced on an object that don’t cancel out and thus cause an acceleration

Free-Body Diagram: a sketch that shows an object and the forces acting on it; also called a force diagram

12B Newton’s Laws of Motion

• From Galileo to Newton

  • Inertia: the tendency of matter to resist changes in its motion

• Newton’s First Law

  • Law of Inertia: the law that states that objects at rest and objects in motion continue in a straight line at a constant velocity unless acted on by a net external force; also called Newton’s first law of motion

• Newton’s Second Law

  • Law of Acceleration: the law that states that the acceleration of an object is directly proportional to the net force acting on the object and is inversely proportional to its mass; also called Newton’s second law of motion

• Newton’s Third Law

  • Law of Action-rReaction: the law that states that for every action force, there is equal and opposite reaction force; also called Newton’s third law of motion

  • Tension: a pulling force that is transmitted through a rope, chain, or similar object

  • Natural Force: the force that acts in a direction that is perpendicular to the surface where two objects make contact

12C Types of Forces

• Gravity

  • Gravity: a field force that acts between the masses of any two objects

  • Law of Universal Gravitation: the law that states that the strength of gravity varies in direct proportion to the masses of the objects involved and inversely to the square of the distant between their centers of mass

• Friction

  • Friction: a contact force that works against the motion of objects trying to move past each other

• Types of friction:

  • Static friction

  • Sliding friction

  • Rolling friction

• Traction: the frictional force between a vehicle’s ires and the road; responsible for accelerating the vehicle

• Centripetal Force: a force that accelerates an object toward the center of a circular path

• Fundamental Force: any one of the four forces that appear to underlie all the other known forces: gravity, strong force, weak force, and electromagnet force