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# CHAPTER 5 NOTES

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1. CHAPTER 5 NOTES KONICHEK

2. I. Dynamics- why objects move the way they do, • A.. kinematics studied how objects move • 1. Isaac Newton- First to study the causes of accelerations • a. summarized them in 3 laws of motion

3. Welcome to the concept of universal forces

4. II.Force- a push or pull • A. 4 types of forces • 1. Gravitational- the force of attraction between all objects • a. weakest of the 4 forces • b. carried by the graviton • 1. only become significant with large amounts of mass.

5. 2. Electromagnetic forces- the forces caused by the charges between particles- • a. carried by the photon • b. produced by the motion of charged particles. The magnetic field and the electric field vibrate at 90 to each other. • 1. act as a single force- electromagnetic force

6. 3. Strong nuclear- this is the force which hold the nucleus together • a. strongest of the 4 forces- 100 times stronger • b. acts for very short distances • 4. Weak force-a form of EM forces • a. decay of some types of nuclei

7. B. Grand unified theory- at some point in time all 4 forces acted as a single unified force • 1. Planck time 10-43 this is the conditions which may explain the big bang • a, all know physics breakdown at this point

8. Isaac and his 3 laws

9. III.Newtons Laws of Motion( Galileo based) • A. First law- an Object with no force acting on it moves with a constant velocity. • 1. unbalanced forces- This is a force which causes motion to occur. • 2. Balanced forces- equilibrium- the sum of all the forces acting on an object is zero • 3. Must assign signs to show the direction of the force • a. positive forces to the right • b. negative forces to the left • 4. To find the net force it is the summation of all the forces acting on the object. • a. if the net force is zero the velocity is zero and no motion results. • 5. Expanding the first law- an Object with no net force acting on it remains at rest or moves with a constant velocity in a straight line.

10. EXAMPLE OF FIRST LAW • POOR LITTLE TEST TUBE

11. Mr. Konichek testing the First Law.wow man!

12. B. Second Law- The acceleration of a body is directly proportional to the net force and inversely proportional to its mass • 1. F=ma • 2. as force increases acceleration must increase • 3. as mass increases and force is constant the acceleration must decrease • 4. The net force on an object causes an acceleration • 5. unit for force- 1 Kgm/s2 = 1 Newton( N)

13. HEY- 2ND LAW EXAMPLES

14. C. Sample problems • 1. what is the net force of an object accelerating at 5m/s2 and has a mass of 500Kg? • 2. What is the acceleration of a 3000Kg truck which has a force of 8000N applied to it?

15. D. Finding force when acceleration must be calculated, given the final velocity, and distance, • 1.initial velocity is zero( Impulse force) • a. Use Vf2= Vi2+ 2ad, solve for a: • a= Vf2-Vi2/ 2d • substitute into F=Ma • F= M(Vf2–Vi2)/2d

16. PRACTICE, PRACTICE • 1. example - a cannon ball with a mass of 60Kg is fired from a cannon at a velocity of 70m/s. the cannon is 2.5m long, assuming the force and acceleration are constant. What would be the force on the cannon ball while it is in the barrel of the cannon? • ASSIGNMENT- PAGE 92 1-4

17. E. Third Law of Motion- For each action force there is an opposite and equal reaction force. • 1. walking, rocket blasting off. • 2. only the force exerted on the object will cause an acceleration.

18. Kick of a gun

19. IV. Using Newton's Laws • A. Mass and weight- • 1. mass- the quantity of matter • 2. weight- The gravitational force exerted by a large body • a. w=mg • b. On earth. 1kg9.8m/s2= 1 Newton

20. B. Types of masses • 1. Inertial mass- The ratio of the net force exerted on an object and it’s acceleration • a. Mi= F/a • 2. Comparison method- Compare the mass of unknown quantity to one of known quantity on a balance. • a. When the pans balance the masses are equal.

21. C. Friction- This is the force between two surfaces which are in contact with each other. • 1. Causes- all surfaces are rough, when they rub against each other there is a weak electromagnetic bond set up between the surfaces • 2. Static Friction- This is the force which opposes the start of motion • a. Have the maximum values of frictional forces • b. Must overcome the static friction when moving something.

22. 3. Sliding friction-The force between sliding surfaces • a. Less that the static friction • 4. Force of friction( assignment P 99- 9 and 10) • a. depends upon the force pushing the surfaces together and the nature of the surfaces in contact. • 1. Ff= MuFn (F=μFn) • a. μ(Mu)= coefficient of friction • b. Fn= Normal force- perpendicular to the line of motion • 1. It’s the sum of all the downward forces on the object. • b. We will assume the coefficient of sliding friction is independent of the surface area and velocity.

23. D. The net force causes acceleration • 1. The acceleration of an object is the result of the net force acting on the object. • 2. The net force is the vector sum of the applied force and the frictional force • a) Fnet= Fapplied + Ffriction • b) Fnet=Fground+ weight • c) throwing up the stone Fn= Fobject+ Weight

24. FREE FALL- • E. The fall of bodies in air • 1. In a vacuum all objects accelerate at the same rate • 2. In the atmosphere objects will fall at different rates because of air resistance • a. drag- The force of the atmosphere against a moving object- form of friction • 3. depends on: • a. size, shape, the air density, and the speed of motion.

25. F. Universal Gravitation- all objects with mass attracts themselves directly proportional to the masses and inversely proportional to the square of the distance. • 1) F= Gm1m1/R2 • 2) G=6.67x10-11Nm2/kg2

26. 4. Falling objects gravity is pulling harder than the drag • a. as the velocity of the object increases the drag increases until the drag force equals the pull of gravity... net force is zero • 1. the object stops accelerating... terminal velocity • 2. a falling parachutist spread eagle falls about 60m/s • 3. with the chute open 5m/s. • PRACTICE PROBLEMS ASSIGNMENT • PAGE 105 :1, P106 :4,6,8,9,10, 12,15,p 107- 22 ,24