1 / 42

Chapter 4: Forces

Chapter 4: Forces. Force and Motion. Objectives. Define a force and differentiate between contact force and long range force . Explain the meaning of Newton’s First Law of Motion and describe an object in equilibrium .

joselynd
Download Presentation

Chapter 4: Forces

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 4: Forces

  2. Force and Motion

  3. Objectives Define a force and differentiate between contact force and long range force. Explain the meaning of Newton’s First Law of Motion and describe an object in equilibrium. Recognize the significance of Newton’s Second Law of Motion and use it to solve motion problems.

  4. Activator: How do Skydivers control their velocity so they can perform team maneuvers? What is the FORCE pulling down? What is the FORCE pushing up?

  5. Force: An object that experiences a push or pull has a force exerted on it. Latin: Fortis (strong)

  6. Contact versus Long-range Forces • Contact Force - A force that acts on the object by touching it. It “makes contact” with it. Con - with; tact (tactile) - touch. Examples: desk on a book, floor on a person. • Long-range Force - A force that acts on the object without touching it. Examples: magnets, force of gravity.

  7. Types of Forces

  8. Free-Body Diagram: A Free-Body Diagram shows all the forces, in vector form, acting on an object. Physical Diagram Free-Body Diagram - A Free-Body Diagram - B

  9. Newton’s First Law of Motion • An object that is at rest will remain at rest or an object that is moving will continue to move in a straight line with constant speed, if and only if the net force acting on that object is zero. • A.K.A. Law of Inertia. Inertia is the tendency of an object to resist change in its current motion. (Example: Car without gas moving or at rest) • Equilibrium: An object is said to be in equilibrium when the net force is zero. (net = sum of all vector forces)

  10. Newton’s First Law of Motion

  11. Newton’s Law of Inertia Paul G. Hewitt Disc One - Newton’s Law of Inertia

  12. Law of Inertia Demo Paul G. Hewitt Disc One - The Old Table Cloth Trick

  13. Cylinder Inertia Demo Paul G. Hewitt Disc One - Inertia of Cylinder

  14. Doing the T.P. Roll Paul G. Hewitt Why you don’t have to hold the T.P. roll

  15. Weight Mass Distinction Paul G. Hewitt Disc One - Weight-Mass Distinction

  16. Newton’s Second Law of Motion • The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object. • a  F net ; a 1 / m ; a = F net / m • Most Common Form: F net = m  a Force = mass x acceleration

  17. Newton’s 2nd Law of Motion Paul G. Hewitt Disc One - Newton’s 2nd Law

  18. All Together Now…. Forces Balanced Unbalanced a = 0 m/s2 a  0 m/s2 a = F net / m Object at Rest Object in Motion Depends directly on Net Force Depends inversely on Mass v = 0 m/s v 0 m/s Stays at Rest Stays in Motion

  19. Using Newton’s Laws Sir Isaac Newton used prisms to show that sunlight was made up of all the colors of the rainbow. This proved that the ancient Greeks ideas about light were wrong.

  20. Friction: What is it? • Frictional resistance to the relative motion of two solid objects is usually proportional to the force which presses the surfaces together as well as the roughness of the surfaces. • Rub your hands together. Feel the heat that is generated. That is friction. Why do we put oil in our car engines? To overcome friction in the pistions.Why can ice skaters glide so easily? How do car brakes work?

  21. Friction: Static and Kinetic

  22. Friction: Static and Kinetic

  23. Friction

  24. Gravity: Feather and Coin

  25. Why do all objects fall at the same rate? Paul G. Hewitt Free-fall Acceleration Explained

  26. Interaction Forces

  27. Objectives • Define Newton’s Third Law of motion. • Explain the tensions in ropes and strings in terms of Newton’s third law. • Define the Normal force. • Determine the value of the normal force by applying Newton’s Second Law.

  28. Newton’s Third Law of Motion • For every action, there is an equal and opposite reaction. • All forces come in pairs. These interaction pairs are equal in magnitude and opposite in direction.

  29. Examples

  30. Interaction Forces

  31. Rifle Recoil

  32. Tensions on Ropes In this simple rope tension diagram, how can you find the tension force in the rope? How does this relate to Newton’s Third Law?

  33. Tensions on Ropes In this simple rope tension diagram, how can you find the tension force in the rope? How does this relate to Newton’s Third Law?

  34. Normal Force The Normal Force is the perpendicular contact force that a supporting surface exerts on another object.

  35. Normal Force The Normal Force is equal to the weight of the object if the supporting surface is horizontal. i.e. FN = Fg = mg

  36. Pressure: The Bed of Nails Paul G. Hewitt Disc One - Pressure: The Bed of Nails

  37. Pressure: The Bed of Nails Why doesn’t the assistant get hurt?

  38. Einstein’s Angels Einstein's Angels

  39. Summary • How would you summarize today’s lesson? • Forces come in interaction pairs that are equal and opposite. • Although the forces are the same in magnitude, the accelerations can vary greatly.

  40. Assignments • Chapter 4 Review Questions 2-30 Evens only, p. 76-77 due Tuesday 11/2. • Study Guide due Thursday. • Quiz next Monday.

More Related