3. The study of Physics begins with mechanics. Mechanics is the branch of physics that focuses on the motion of objects and the forces that cause the motion to change. There are two parts to mechanics: Kinematics and Dynamics. Kinematics deals with the concepts that are needed to describe motion, without any reference to forces. Chapter 1 Dynamics deals with the effect that forces have on motion. Chapter 2

4. Dynamics is that branch of mechanics which deals with the motion of bodies under the action of forces. Dynamics has two distinct parts: kinematics and kinetics. Kinematics is the study of motion without reference to the forces which cause motion. Kinetics relates the action of forces on bodies to their resulting motions.

6.  A push or pull on an object.  Described by:  A force gives an object energy to: STRENGTH DIRECTION STOP MOVING START MOVING CHANGE DIRECTION

7.  A push or pull on one object by another that is touching it.  Contact forces can be:  Strong OR  Weak

8.  A force that one object can apply to another object without touching it.  Examples Include:  Gravity  Magnetic Force  Electric Force

9.  Force is a VECTOR quantity  can be used to show forces.  The of an arrow shows the of the force.  The that the arrow points shows the direction in which the  The stronger the force the the arrow. ARROWS DIRECTION LENGTH STRENGTH FORCE WAS APPLIED LONGER

10.  The SI unit for force is the  The symbol for Newton is  One Newton = about the force you exert to lift a lime.  Named after: NEWTON N Sir Isaac Newton (founder of physics)

11.  Gravity is NOT “the force that pulls you down!”  Gravity attracts all objects with mass inward towards other objects with mass.

12.  An attractive force that exists between all objects that have mass. The force of gravity is NOT the same as the acceleration DUE to gravity! Force of gravity - the force exerted by the gravitational field of a massive object on any body within the vicinity of its surface.

13.  Sir Isaac Newton (1600’s)  The law states: Three factors that affect the force of gravity Mass of object 1 Mass of object 2 Distance between each All objects are attracted to each other by a gravitational force. The strength of force depends on the MASS of each object and the DISTANCE between them.

14.  When the mass of one or both objects the gravitational force between them also  Regardless of the amount of mass an object has the will be the  Each object exerts the attraction on the other object. INCREASES FORCE ARROWSSAME SIZE SAME

15.  The amount of matter in an object.

17.  The attraction between objects as the between the object DECREASES DISTANCE INCREASES

18. http://www.physicsclassroom.com/class/circles/Lesson-3/Newton-s-Law-of- Universal-Gravitation

19.  The gravitational force exerted on an object.  Weight is measured in  Near Earth’s surface the object’s weight is the NEWTONS FORCE DUE TO GRAVITY

20.  Weight and mass are related, but ARE NOT the same.  Weight can due to  Mass change FORCE = CHANGE GRAVITY DOES NOT MASS x ACCELERATION F = Weight on Earth = M x A MASS x 9.8m/s 2 (acceleration due to the force of gravity)

21.  What would an object with a mass of 10 kg weigh?  If your mass was 50kg, what would your weight be?

22.  The combination of all the forces acting on an object.  To calculate the net force: ◦ If the forces act in the same direction they are added together. ◦ If forces act in opposite directions they are subtracted.

23.  Forces acting on an object that combine and form a net force that is not zero.  Unbalanced forces cause an object to move.  Forces moving in the same direction are  Forces moving in the opposite direction are ADDED SUBTRACTED

24.  Forces acting on an object that combine and form a net force of ZERO. NO change in motion.

25.  Objects whose only acceleration is due to gravity are in free fall.  All free falling objects accelerate at the same rate regardless of their mass.  Rate of acceleration due to gravity on Earth = (9.8 m/s 2 )  Galileo and his experiment ◦ Objects of the same mass fall to Earth at the same rate but do not hit the ground with the same force.

26.  If the velocity and time for a free-falling object being dropped from a position of rest were tabulated, then one would note the following pattern.  Time (s)Velocity (m/s)  00  1- 9.8  2- 19.6  3- 29.4  4- 39.2  5- 49.0

27.  Earth’s atmosphere is contained of a blanket of different gasses.  Although all objects fall at a rate of 9.8m/s 2 those air molecules exert an upward force (friction) between the air molecules and the object’s surface. ◦ This type of friction is called “drag” or “fluid friction”  The greater the surface area of the falling object, the more air molecules the object hits. Therefore there will be more drag on the object causing acceleration to decrease.

28.  The speed when a falling object is no longer getting faster. ◦ Velocity – how fast something is changing position (both speed and direction)  Occurs at the moment force due to gravity (weight) is equal to the opposite force of air resistance (friction or drag)  What do you think would happen if we dropped a penny off of the Empire State Building? Find the Answer Here!Find the Answer Here!

29. Consider a skydiver: 1)At the start of his jump the air resistance is _______ so he ____ downwards. 2) As his speed increases his air resistance will _______ 3) Eventually the air resistance will be big enough to _______ the skydiver’s weight. At this point the forces are balanced so his speed becomes ________ - this is called TERMINAL VELOCITY zero accelerates increase balance constant Credit to: W RichardsCredit to: W Richards Worthing High School

30. How the forces change with time. KEY Weight (constant value and always present) Air resistance (proportional to the speed) Resultant force (the bigger the unbalanced force the greater the acceleration)

31. Consider a skydiver: 4) When he opens his parachute the air resistance suddenly ________, causing him to start _____ ____. 5) Because he is slowing down his air resistance will _______ until it balances his _________. The skydiver has now reached a new, lower ________ _______. increases slowing down decrease weight terminal velocity Click Here to Watch Skydiver

32. Velocity Time Speed increases… Terminal velocity reached… Parachute opens – diver slows down New, lower terminal velocity reached Diver hits the ground

33. Determine the acceleration of this 85 kg skydiver at points A-D. (Hint: F=ma) 9.8 m/s 2 5.68 m/s 2 1.56 m/s 2 0 m/s 2

34. Two-dimensional motion of an object horizontal Vertical Horizontal

35.  Horizontal ◦ Motion of a ball rolling freely along a level surface ◦ Horizontal velocity is ALWAYS constant  Vertical ◦ Motion of a freely falling object ◦ Force due to gravity ◦ Vertical component of velocity changes with time  Parabolic ◦ Path traced by an object accelerating only in the vertical direction while moving at constant horizontal velocity

36.  When both components are linked together using a common factor you get Projectile Motion in 2 dimensions!

37.  Friction is a force that resists the motion. ◦ Friction involves objects in contact with each other ◦ Friction must be overcome before motion occurs.  Types of friction STATIC FRICTION SLIDING FRICTION FLUID FRICTION

38.  Friction always “opposes motion”  Friction always pushes opposite to the object’s motion.  Friction can slow down or stop an object!

39.  Walking  Tying your hair back  Tying a knot  Erasing your mistakes  Writing with a pencil  Mechanical Gears…no cars, planes, phones, computers..and more!  Brakes on your car  Your clothing wouldn’t even stay together!!!

40.  Friction has proved to be a very powerful force, even with everyday objects! ◦ Click here for the phonebook challenge Click here for the phonebook challenge

41.  Friction that acts on objects that are not moving.  The force that overcomes static friction is an applied force that is parallel to the surface of contact.

42.  Frictional force between objects that are sliding with respect to one another.

43.  A force produced by a fluid (gases or liquids) Examples: engine oil, grease  Air resistance  Air resistance is affected by: *objects with more surface area have more air resistance** SHAPE SIZE MASS a type of fluid friction Upward force exerted on falling objects.

44. 2 causes of friction  When microscopic dips and bumps that cover surfaces slide past another surface with dips and bumps they catch on to one another.  When a positive charge slides by a negative charge attraction occurs.

45. This is why when two objects or two surfaces interact (touch), there will be friction. A microscopic view shows every surface has tiny ridges and bumps.

46. Magnified section of a polished steel surface showing surface bumps about 5 x 10 -7 m (500 nm) high, which corresponds to several thousand atomic diameters. Computer graphic from a simulation showing gold atoms (below) adhering to the point of a sharp nickel probe (above) that has been in contact with the gold surface. Surface Roughness Adhesion