2 MechanicsThe branch of physics involving the motion of an object and the relationship between that motion and other physics conceptsKinematics is a part of mechanics that studies motion in relationship to time.In kinematics, you are interested in the description of motionNot concerned with the cause of the motion (Dynamics)
3 Quantities in Motion Any motion involves three concepts DisplacementVelocityAccelerationThese concepts can be used to study objects in motion and called the parameters of the motion.
4 DisplacementDefined as the change in position of a body when it moves from an initial position to a final positionf stands for final and i stands for initialMay be represented as s or y if verticalUnits are meters (m) in SI.Vector quantity
5 Displacement Displacement is a vector quantity. Needs both magnitude and direction to be completely describedGenerally denoted by:boldfaced and an arrow over the letter+ or – sign is also used if motion is along one direction: ∆s = +70, ∆s =-60
6 Displacement Versus Distance The displacement of an object is not the same as the distance it travelsExample:In the adjacent picture, what is the displacement?What is the approximate distance traveled?
7 Kinematic Concepts- Speed Is the rate at which distance is covered by an object.Or the distance covered per unit timeScalar quantityTwo types of speed:Average speedInstantaneous speed
8 Average vs Instantaneous Speed Average Speed is the ratio of the total distance (d) covered by the object to the time interval (t) over which the distance was covered.Average Speed (v) = total distance (d) total time (t)Average speed does not tell us about the variation in the speed throughout the journey.Instantaneous Speed is the speed at a specific instant of time.
9 Be Knowledgeable!Distinguish between Instantaneous and average speed. (May marks)average speed is the speed over a period of time/distance;instantaneous speed is the speed at a particular instant in time/point in space;
10 Kinematic Concepts- Velocity Is the rate at which displacement is coveredVelocity is a vector quantityAverage vs instantaneous velocityThe average velocity is the ratio of the total displacement (∆s) covered by the object to the time interval (∆t) over which the displacement was covered.Average velocity= = total displacement = ∆𝑠 ∆𝑡 total time
11 Instantaneous Velocity Is the velocity at any one instantv = s tWhere t is tending towards zeroThe instantaneous velocity of an object at point P is its velocity at the instant it passes P and is the average velocity of the object calculated over a infinitely small (but not zero) distance around P.
12 Speed vs. VelocityCars on both paths have the same average velocity since they had the same displacement in the same time intervalThe car on the blue path will have a greater average speed since the distance it traveled is larger
13 AccelerationWhen the velocity of an object changes, we say that it acceleratesVelocity can change by:Changing its magnitude, and/orChanging its directionAcceleration is the rate at which velocity is changing or change in velocity per unit timeAcceleration is a vector quantitySI Unit is ms-²u and vo are also used for vi
14 More about Acceleration The above equation refers to average acceleration that takes place over a period of timeInstantaneous acceleration refers to a specific instant of time when the time interval ∆t tends to zero.
15 Uniform Motion Constant velocity Constant direction, andConstant speedAcceleration is zero (Velocity shown by red arrows maintaining the same size)
16 Graphical analysisWhat information can we get from the ticker tape and from the graphs?
17 Graphical analysisWhat information can we get from the ticker tape and from the graphs?
18 Graphing Motion –Uniform Motion in the positive sense Acc = 0Velocity is positive and constant= 12 (unit)Position-time graph is a straight increasing line whose slope is equal to the velocity (12)Area under the velocity-time graph gives the displacement of the object (Area = 12 * 15 = 180)
19 Graphing Motion –Uniform Motion in the negative sense Acc = 0Velocity is negative and constant ( -12). The negative sign means that the object is moving in the negative sense.Position-time graph is a straight decreasing line whose slope is equal to the velocity ( -12)Area under the velocity-time graph gives the displacement of the object (-12 * 15 = -180)
20 Notions about Uniform motion Graphs Uniform motion Displacement-time graph:the graph is a straight lineGradiant is the uniform velocityPositive gradient: object moving forwardNegative gradient: object moving backwardsUniform motion Velocity-time graph:the graph is straight horizontal lineArea under graph gives the change in displacementPositive area: positive displacementNegative area: negative displacement
21 Be a Thinker!The above graph shows four different phases of motion. For each phase:Identify the type of motion and directionFind the velocityDraw the velocity-time graphFor the whole journey, determine:the total displacement and total distance.the average velocity and average speed.