1. FORCES AND CIRCULAR MOTION

2. A. Definition: a push or pull acting on a mass 1. Force is a vector quantity with both magnitude (numeric value) and direction 2. Force can be broken down intohorizontal and vertical components 3. Symbol: 4. Units: I. FORCE Newtons ! (N) F

3. B. Concurrent Forces: many forces acting on the same object at the same time. 1. Treat all forces individually to find a resultant force (break into components) 2. This resultant of all concurrent forces is called the Net Force F net Symbol :

4. C. Free Body Diagram: represents concurrent forces acting on an object

5.  Two Physics students try pushing a car to see who is stronger. One student pushes west with a force of 500 Newtons. The other pushes East with a force of 700 Newtons.  Draw a free body diagram of the situation.  What is the Net Force?  What way does the car move? EXAMPLE 1: NET FORCE

6.  Two Physics students are again arguing and this time are in a tug of war. They are pulling on a box. One student pulls 30 degrees toward the northeast with a force of 400 Newtons and the other pulls at 20 degrees toward the Northwest with 500 Newtons.  Draw a free body diagram of the situation.  What is the Net Force? EXAMPLE 2: NET FORCE

7.  What is net force on a box of mice being pulled with a force of 20 Newtons due West toward a snake pit and another force of 30 Newtons pulling due East toward an alley filled with cats, a 50 Newton force pulling due North toward a cliff, and a 50 Newton force pulling due South toward a large pond?  Draw a Free Body Diagram 1 st !!! JOURNAL #11 10/1

8. D. Static Equilibrium: reached when the resultant of all forces acting on an object is ZERO (balanced) 1. At Equilibrium, objects remain at rest or constant velocity. F net = Zero F net ≠ Zero

9. 2. Net Force is equal to ZERO in static situations F net =0

10.  What forces MUST be added in order to produce static equilibrium in the free body diagram below? EXAMPLE: STATIC EQUILIBRIUM

11. II. DYNAMICS A. Newton’s First Law: An object maintains a state of equilibrium unless acted on by an unbalanced force. (at rest or constant velocity) 1. Any unbalanced force ( F net ≠ 0) will produce a change in an object’s velocity…either speed, direction, or both. the object will ACCELERATE 2. Newton’s First Law is also known as the Law of Inertia Inertia: the resistance of an object to a change in its motion  More Mass = More Inertia Effects of forces acting on objects (Newtons Laws of Motion)

13. Masses resist changes in motion…

14.  What has more inertia? A 10 kg bag of feathers sitting still or a 5 kg gold bar moving along at 10 m/s?  What has more inertia? A 20 kg baseball sitting on a stand, or a 5 kg bowling ball moving along at 30 m/s? EXAMPLES: INERTIA

15. B. Newton’s Second Law: the acceleration of an object is directly proportional to the net external force acting on an object and inversely proportional to the object’s mass. force is related to mass and acceleration using the famous expression: acceleration is produced by force(s) increasing force will increase the acceleration

16. 1. Units for Force…Yay!! Dimensional Analysis! a. Newtons are the SI unit of force and are a derived unit (combination of fundamental units) b. 1 Newton is equal to the force required to accelerate a 1 kilogram mass 1 meter per second squared

17. 2. Increasing mass will increase the force needed to accelerate that mass larger m  larger F net *The equation must balance!

18.  m   a 3. If the force is constant, then increasing the mass of an object will decrease the resulting acceleration  F net   a

19. 4. Graphing F net = ma : Force (N) Acceleration (m/s 2 ) Direct Relationship: Increasing Force produces more acceleration

20. A capybara with a mass of 100kg is tackled by a Jaguar with a steady force of 100 N along the ground. Assuming no friction, what is the acceleration of the rodent? EXAMPLE: NEWTON’S 2 ND LAW

21. C. Newton’s Third Law: when one object exerts a force on a second object, the second object exerts a force on the first that is equal in magnitude, but opposite in direction.  For every action there is an equal and opposite reaction!

22. What happens to a boat when you step onto a dock? Newton’s 3 rd Law!!!

23.  Newton’s 3rd Law also applies in space when making objects move

24. A. Weight: gravitational force exerted on a small mass by a planet/large body 1. Weight CHANGES based on what planet/object you are on… MASS does NOT CHANGE 2. Symbol: 3. Units: 4. Equation: III. NATURAL FORCES Newtons ! (N) How much do you weigh? How much do you weigh?

25. EXAMPLE: WEIGHT  The fattest, ugliest Capybara has a mass of 66 kg. What is the weight of the rodent on Earth?  Convert the mass to pounds if 1 kilogram = 2.2 pounds

26. B. Newton’s Universal Law of Gravitation: Describes the force of attraction between different masses.  Any two bodies attract each other with a force that is directly proportional to the product of their masses, and inversely proportional to the square of the distance between them

27. F g F g = Gravitational Force G G = Universal Gravitational Constant = 6.67 x 10 -11 Nm 2 /kg 2 m 1 m 1 = mass of object 1 m 2 m 2 = masses of object 2 r r = distance between the two masses On Your Reference Tables!! (Front Cover)

28. Graphical Representation:

29. What is the force of gravitational attraction between the Earth and the Moon? m 1 m 1 = Earth = 5.98 x 10 24 kg m 2 m 2 = Moon = 7.35 x 10 22 kg r r = 3.84 x 10 8 m G G = 6.77 x 10 -11 Nm 2 /kg 2 EXAMPLE: NEWTON’S UNIVERSAL LAW OF GRAVITATION

31. 2. Gravitational Fields: vectors are used to show gravitational force  A “unit test mass” will accelerate along gravitational field lines, toward the center of the source of gravity