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10/30/13

10/30/13. Bull’s Eye Lab Our Own Hot Wheels Challenge Projectiles and Pumpkins Isaac Newton. 11/4/2013. Turn in Bullseye Lab by 3:15 Pumpkins and Projectiles? Hey remember that scientific method activity? And so it comes to this, the mind blowing Sir Isaac Newton and his laws of motion

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10/30/13

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  1. 10/30/13 • Bull’s Eye Lab • Our Own Hot Wheels Challenge • Projectiles and Pumpkins • Isaac Newton

  2. 11/4/2013 • Turn in Bullseye Lab by 3:15 • Pumpkins and Projectiles? • Hey remember that scientific method activity? • And so it comes to this, the mind blowing Sir Isaac Newton and his laws of motion • Newton’s Laws

  3. 11/5/2013 • Pumpkins and Projectiles? • And so it comes to this, the mind blowing Sir Isaac Newton and his laws of motion • Newton’s Laws

  4. 11/1/12 • Shooting the Moon • Normal Force • Tug of war physics, oh…okay • Vectors in multiple directions!

  5. 10/30/2012 • Bullseye Lab • Shooting the Moon • Newton’s Third Law

  6. 11/6/2013 • Turn in Homework! • That’s some good inertia • What is this Force? (not that force) • Newton’s 1st and 2nd Law Demos

  7. Newton’s First Law: Inertia An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

  8. First Law: Application Center of gravity (mass)

  9. What is a Force?

  10. First Law - Inertia Law of Inertia – every object continues in a state of rest, or of motion in a straight line at a constant speed, unless it is compelled to change that state by forces exerted upon it.

  11. First Law:

  12. Inertia Concepts Mass – the more mass an object has, the greater its inertia and the more force it takes to change its state of motion. Mass is the measure of the inertia of an object.

  13. 11/7/2013 • Turn in Homework! • That’s some good inertia • What is this Force? (not that force) • Newton’s 1st and 2nd Law Demos

  14. Representing Forces... • Forces are vectors • Forces are drawn as arrows, the length represents the magnitude and the direction of the arrow is the direction of the force. • forces add like vectors. • the sum of all the forces is called the net force. • A picture of a body with arrows drawn representing all the forces acting upon it is called a FREE BODY DIAGRAM.

  15. Try it... Draw a picture of your book sitting on the desk. Identify all the forces acting on it.

  16. Free Body Diagrams... T (table) Book W (weight)

  17. Free Body Diagrams... What forces are acting on a skier as she races down a hill?

  18. Plane Free Body Diagram

  19. Free Body Diagrams

  20. 11/14/2013 • Test Make-ups • Newton’s 2nd and 3rd Laws • Newton’s Laws Work

  21. Newton’s Second Law:The Law of Acceleration When an unbalanced force is applied to an object it will accelerate in the direction of the net force with an acceleration proportional to the force applied. F = m x a a = F/m Forces cause accelerations!

  22. What is a "newton?" F = ma Mass = kg Acceleration = m/s2 Force = kg ·m/s2 Newton (N) = kg ·m/s2

  23. Examples • A jet thruster applies a force of 20,000N at maximum burn. If the jet has a mass of 5,500 kg what is the acceleration of the jet? How long will it take to increase speed from 0 m/s to 80 m/s?

  24. 11/15/2013 • Test Make-ups • Newton’s 2nd and 3rd Laws • Newton’s Laws Work

  25. Examples • What force is needed to decelerate a 15,000 N car from 18 m/s to rest in 6 seconds?

  26. Think About it... • A textbook rests on a table. What forces act on the book? On the table? • True or False. When you jump the Earth accelerates. • An 8 ton bus crashes into a 1200 lb VW Rabbit. If the bus applies a force of 20,000 lb on the car, what is the force of the car on the bus?

  27. Second Law of Motion Newton was the first to realize that the acceleration produced when we move something depends not only on how hard we push or pull, but also on the object’s mass. The acceleration produced by a net force on an object is directly proportional to the magnitude of the net force and is inversely proportional to the mass of the object.

  28. Third Law: Action - Reaction

  29. The Law of Force-Counterforce • unaccompanied forces do not exist in nature. • ‘action-reaction’ forces are not the same as ‘balanced’ forces. When one body exerts a force on another body the second one exerts an equal and opposite force on the first.

  30. Third Law: Action - Reaction • Whenever a first body exerts a force F on an second body, the second body exerts a force -F on the first body. F and –F are equal in magnitude but opposite in direction. • The law of action reaction

  31. Newton’s Third Law and the Grasshopper

  32. 11/18/2013 • Homework • Forces in Balance • Action-Reaction Lab • Balloon force • Newton’s Laws Work

  33. According to legend, a horse learned newton's laws. When the horse was told to pull a cart, it refused, saying that if it pulled the cart forward, according to Newton's third law, there would be an equal force backwards: thus there would be balanced forces, and the cart would not accelerate. How would you reason with this horse?

  34. Interaction Pairs Two forces that are in opposite directions have equal magnitude. You push your friend, this does not cause your friend to exert a force on you. The forces exist together or not at all.

  35. Forces in Equilibrium The conditions for a particle to be in equilibrium • Necessary conditions for an object to settle into equilibrium (all things in balance, no change in motion): SF = 0

  36. Dog Fight • Susan is holding her dog, its’ mass is 8.0 kg, when Allen decides that he wants it and tries to pull it away from Susan. • If Allen pulls horizontally on the dog with a force of 10 N and Susan pulls with a horizontal force of 11 N in the opposite direction, what is the horizontal acceleration of the dog?? • Why doesn’t the dog bite one of them?

  37. Normal Force The perpendicular contact force exerted by a surface on another object.

  38. 11/19/13 • Drag force • Tug of war physics, oh…okay • New Lab: Balloon Cars

  39. Drag Force • Is it true that particles in the air around an object exert forces on it? • Yes, a huge force, but they all balance, and there is no net effect. • What if the object is moving through the air? • It experiences a drag force • Drag Force: the force exerted by a fluid on an object moving through a fluid. • There is a direct relationship between the magnitude of the drag force and the surface area of a moving object.

  40. Terminal Velocity The constant velocity that is reached when the drag force equals the force of gravity.

  41. TUG OF WAR in Physics Which of Newton’s laws are involved? How do you determine the winner?

  42. What is Friction? • Friction is the force resisting the relative lateral (side to side) motion of solid surfaces, fluid layers, or material elements in contact. • So far we have neglected friction, but since it is all around us, it is worth treating.

  43. Two Main Types of Friction • Push a book across a desk, it experiences a type of friction that acts on all moving bodies. • KINETIC FRICTION (Fk) a force that is exerted by one surface against another when the two surfaces rub against each other because one or both of the surfaces are moving.

  44. 11/20/2013 • Friction Force • New Lab: Balloon Cars

  45. Two Main Types of Friction • Now try pushing a heavy couch across the floor, give it a push, and it stays where it is. Why? • STATIC FRICTION (Fs) the force exerted on one surface by another when there is no motion between the two surfaces.

  46. 11/21/2013 • Friction Force • New Lab: Balloon Cars HW

  47. *** At Constant Velocity: Fapplied = Friction Force a = 0 Fnet= 0

  48. *** When object is moving on a horizontal surface, the normal force equals ..... …the weight force.

  49. Fn= weight force = w = mg On a horizontal surface:

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