Transcript Document
Concept Summary Batesville High School Physics Aristotle’s View Two types of motion: Natural motion - what an object “naturally wants to do” Violent motion - what an object has to be forced to do Aristotle’s View In order for a “normal” object to move at constant velocity, something must be pushing on it. When the pushing stops, the object (perhaps gradually) comes to a stop. Galileo’s View Realized that the classical view of motion did not recognize the role of friction If left to themselves, moving objects don’t slow down. Newton’s First Law Whatever an object is doing, that’s what it wants to keep doing. If left to themselves, objects will keep doing whatever they’re doing. Newton’s First Law Objects at rest tend to stay at rest. Objects in motion tend to stay in motion. Newton’s First Law If there is no net force on an object, the object won’t accelerate. Newton’s First Law The converse is also true: If an object is not accelerating, then there is no net force on it. What is an “object”? Anything “object”. made of matter is an What is a “force”? A force is an interaction between 2 objects involving a push or a pull. Forces are vectors - they have a direction in space. Common units of force are: pounds, Newtons, or dynes. What is a “net force”? The net force on an object is the vector sum of all of the forces that push or pull on the object. “no net force on an object” means: either there are no forces on the object, or: the forces that push or pull on the object all cancel exactly. “object won’t accelerate” means: the object: won’t speed up. won’t slow down. won’t change direction. Newton’s First Law can be stated: If no forces push or pull on an object, or if the forces that do push or pull on it all cancel exactly, then the object will not speed up, slow down, or change direction. Inertia Newton’s First Law says that objects do not accelerate spontaneously. This property of matter, which causes objects to resist acceleration, has been named “inertia”. Newton’s First Law is often called the Law of Inertia. Equilibrium An object that is not accelerating is said to be “in equilibrium.” If an object is at rest and not accelerating, it is said to be “in static equilibrium.” Newton’s First Law Again If an object is in equilibrium, the net force on it is zero, and If the net force on an object is zero, the object is in equilibrium. Friction Friction is a force that arises due to the relative motion of two surfaces. Two solid surfaces - sliding friction, rolling friction A solid and a fluid - air resistance Two fluids Friction The direction of the friction force always opposes the relative motion of the surfaces. Friction The amount of sliding friction depends on: The condition (smoothness/roughness) of the surfaces The normal force between the surfaces The End Friction The amount of sliding friction does not depend on: Area of contact Relative speed