Changes In Motion Chapter 4 section 1

What is Change in Motion?

Force  Force – A push or pull exerted on some object.  Usually a force represents the interaction of an object with its surrounding environment.

What does a force do?  A force causes an object to change its state of motion.  Examples:  An object at rest that is pushed to make it move from its original position.  An car moving at a constant velocity suddenly slows down or speeds up.

SI Units for Force  The SI unit for force is a “Newton.”  Named after Sir Isaac Newton ( ), whose work contributed to the modern understanding of force and motion, as well as light. He is also created with discovering the mathematical field of calculus.

What is a Newton?

Contact Forces  Contact Force – Force that arises from the physical contact of two objects.  Example:  Pulling a wagon  Pushing a desk  Anything that is a push or pull acting on an object caused by another object.

Field Force  Field Force – Force that can exist between objects, even in the absence of physical contact between the objects.  Example:  Gravity  Electromagnetism  Weak Nuclear  Strong Nuclear

Force Diagrams  A force is a vector, which has both magnitude and direction.  The magnitude is how hard of a push or pull that is exerted on an object.  The direction is where the force is applied to an object.  Since a force is a vector, it can be drawn with an arrow and shown through a picture called a force diagram.

Force Diagram  Force Diagram – A diagram of objects involved in a situation and the forces exerted on the objects.  When drawing force vectors on an object, the tail is placed at the center of mass and the point goes in the direction of the force.

Force Diagram Example

Free-Body Diagram  A free-body diagram is used to analyze only the forces affecting the motion of a single object. Diagram Force Diagram Free-Body Diagram Diagram Force Diagram Free-Body Diagram

Labeling a Free-Body Diagram  Variables used to describe forces:  W or mg or F g = Gravitational Force  T or F T = Tension Force  F push or F p = Compression Force  n or N or F n = Normal Force  F f = Friction Force