4 B Kinematics Describing Motion Kinematics measures Position

4 B Kinematics – Describing Motion Kinematics measures – Position – Speed or velocity – Acceleration What is motion? System’s position changes during an interval of time

Distance vs Displacement Distance: length that was traveled – Scalar, positive number with units Displacement: overall change in position – Shortest distance between positions & direction – Measured from origin (start position) – Vector

Speed How fast something moves Distance _______ Speed = Time The rate at which distance is covered Distance is covered per unit of time per = “divided by”

Speed We define speed of an object as SPEED = Distance traveled Time elapsed For example, 30 miles per hour means object travels distance of 30 miles in an elapsed time of one hour. Write as, miles 30 miles per hour = 30 hour 21 -Dec-21

Speed and Distance From definition of speed, (Distance traveled) = (Speed) X (Time elapsed) Example: If speed is 30 miles per hour and time elapsed is 2 hours then distance traveled is (30)X(2) = 60 miles. Match units: This time elapsed is also 120 minutes but it’s not correct to compute distance traveled as (30)X(120) = 3600 miles {WRONG}. 21 -Dec-21

Average versus Instantaneous Say it takes you one hour to drive the 30 miles from home to school. Average speed is 30 miles per hour. Instantaneous speed (given by speedometer) varies due to traffic, stop lights or cows in the road, etc. 21 -Dec-21

Velocity Speed and velocity are used interchangeably In physics velocity = speed in a given direction Ex: 10 m/s north v = d / t and a direction

Velocity is speed and direction of object’s motion. Examples: 30 miles per hour, Northward 25 meters per second, Downward 300 miles per hour, Coming towards you 21 -Dec-21 25 m/s, upward 25 m/s, downward Same speeds Different velocities