1. Kinematics

2. Classical Mechanics Classical Mechanics: Kinematics: Dynamics:
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

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

4. Kinematics – Getting Started
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…’)

5. Position - Where Where: x, y, or z Change in Position (Δ…)
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)

6. How Fast? Rate at which the position changes Average Velocity ( )
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

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

8. Acceleration The rate at which velocity changes
Kinematics
The rate at which velocity changes
Average acceleration ( )
Vector SI Unit: m/s2
Difference between an acceleration of 3 m/s2 and 16 m/s2?

9. Directions Positive and negative:
Kinematics
Positive and negative:
Tell DIRECTION, not magnitude
Which is a larger acceleration? -25 m/s2 or 22 m/s2

10. Kinematic Equations Condition: a must be constant Assumptions:
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)

11. 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.

12. 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?

13. 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)
4 times as far
The same distance
2 times as far
The mass of the car must be known