1. Changes In Motion Chapter 4 section 1

2. What is Change in Motion?

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

4. 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.

5. SI Units for Force  The SI unit for force is a “Newton.”  Named after Sir Isaac Newton (1642-1727), 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.

6. What is a Newton?

7. 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.

8. 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

9. 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.

10. 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.

11. Force Diagram Example

12. 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

13. 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