Physics 151 Week 7 Day 2 Topics  What is a Force?  Newton’s 0th Law of Motion (Not in the book)  Force Diagrams and System Schemas (Not in the book)  Newton’s 1st Law of Motion  More vector math

Slide 2-34 Vectors and Vector Components: Example Displacement with 3 motion intervals

Slide 2-34 Vectors and Vector Components: Example Velocity in 2D and vector equations

Clicker Question 1 1. A “net force” is A.the sum of the magnitudes of all the forces acting on an object. B.the difference between two forces that are acting on an object. C.the vector sum of all the forces acting on an object. D.the force with the largest magnitude acting on an object. Slide 4-7

Answer 1. A “net force” is A.the sum of the magnitudes of all the forces acting on an object. B.the difference between two forces that are acting on an object. C.the vector sum of all the forces acting on an object. D.the force with the largest magnitude acting on an object. Slide 4-8

What Is a Force? A force is a push or pull.... acts on an object.... requires an agent.... is a vector.... is a contact force or a long-range force. Slide 4-10

Slide 2-34 Newton’s Zeroeth Law of Motion Objects are dumb - They have no memory of the past and cannot predict the future. Objects only know what acts directly on them in a given moment.

Types of forces

Contact Forces vs. Non-contact Forces

Defining normal Forces and Friction Forces Contact forces arise when two objects interact due to surfaces in contact. These forces can be broken into two components parallel and perpendicular to the surface The component parallel to the surface is the friction force The component perpendicular to the surface is the normal force. (normal is a mathematical term meaning perpendicular.)

Normal Force n  Slide 4-22

Friction f k and f s   Slide 4-23

Tension ForceT  Slide 4-21

Drag D and Thrust F thrust  Slide 4-24

Force Vectors Slide 4-18

Free-Body Diagrams You should always describe a force by identifying the type of force, the force agent and the object being acted on. For a force diagram label forces like this => F g, Earth=>box

System Schema Draw a system schema: Draw a diagram where you write down the name of each object in the system and then draw a solid circle drawn around it. Draw two sided arrows like this between the object circles of objects that interact (This illustrates all interactions between the objects in this diagram). Draw an additional dotted line around the block to indicate it is the object of interest. This diagram is called a system schema. A system schema illustrates all the relevant interactions between the objects in a given physical situation Each double-headed arrow represents an action-reaction pair of forces A.K.A. a Newton’s 3rd Law pair

Slide 2-34 Identifying Forces: Freebody (Force) Diagrams and System Schema

Example Problem: One book, Two book Slide 4-26

Newton's First Law of Motion DEMO - Pushing the cart on track DEMO - Hoverpuck => How much force is need to make an object move with constant velocity?

Example Problem The hover puck Slide 4-26

What Causes Motion? In the absence of any forces acting on it, an object will continue moving forever. Motion needs no “cause.” Slide 4-8

Newton's First Law of Motion Every object continues in a state of rest or a state of motion with a constant speed in a straight line unless acted on by an unbalanced force. or Velocity = constant if and only if (IFF) F net = 0

Seat Belts: An Application of Newton’s First Law Slide 4-16

Newton's First Law of Motion Demonstrations DEMO - Smash the HAND DEMO - Tablecloth

An elevator, lifted by a cable, is going up at a steady speed. Identify the forces acting on the elevator. Is T greater than, equal to, or less than w? Or is there not enough information to tell? A => F T > F g B => F T = F g C => F T < F g Example Problem Slide 4-30

Summary Slide 4-39