Kinematics Classical Mechanics Kinematics Classical Mechanics The study

Kinematics

Classical Mechanics Kinematics • Classical Mechanics: – The study of motion related to concepts of force and energy • Kinematics: – Description of how objects move • Dynamics: – Study of forces which cause objects to move

Kinematics – Getting Started • Translational Motion: – Movement without rotation • Motion with a reference frame: – Motion in reference to a set axis Kinematics

Kinematics – Getting Started Kinematics • Scalar - Magnitude only, plus a unit • Vector - Magnitude and direction, plus a unit • Time: t • SI Unit (metric): Seconds (s) • Elapsed time: Δt • Δ Delta (‘change in…’)

Position - Where Kinematics • Where: x, y, or z • Change in Position (Δ…) • Displacement - Shortest straight-line distance between two points Vector SI Unit: meters (m) • Distance - Entire path taken between two points Scalar SI Unit: meters (m)

How Fast? Kinematics • Rate at which the position changes • Average Velocity ( ) displacement time Vector SI Unit: m/s • Average Speed distance Average Speed = time Scalar SI Unit: m/s

Problems with Averages Kinematics • Averages at times don’t tell the entire story • Instantaneous Velocity: velocity measured during an infinitesimally short time interval

Acceleration Kinematics • The rate at which velocity changes • Average acceleration ( • Vector ) SI Unit: m/s 2 • Difference between an acceleration of 3 m/s 2 and 16 m/s 2?

Directions Kinematics • Positive and negative: – Tell DIRECTION, not magnitude • Which is a larger acceleration? -25 m/s 2 or 22 m/s 2

Kinematic Equations Kinematics • Condition: a must be constant • Assumptions: Δt = tf – to = (starting from to of zero) = t xo = starting position (most of the time is also x = 0 m)

Example 1 Kinematics A car goes down a certain road at an average speed of 40 km/h and returns along the same road at an average speed of 60 km/h. Calculate the average speed in km/h for the round trip.

Example 2 Kinematics A car traveling 88. 0 km/h is 110 m behind a truck traveling 75 km/h. How long will it take the car to reach the back of the truck?

Example 3 Kinematics The driver of a car makes an emergency stop by slamming on the car’s brakes and skidding to a stop. How far would the car have skidded if it had been traveling twice as fast initially? (Neglect any reaction time) A. 4 times as far B. The same distance C. 2 times as far D. The mass of the car must be known