Speed, Velocity, and Acceleration SPH3U UNIT 1: KINEMATICS

Warm-up: Challenge Question!  A robotic toy airplane is flies 32 meters [N 40° W] and then turns and flies 15 meters [N 12° E]. What is the total displacement?

Recall  In Physics, we measure things in vector quantities and scalar quantities. Vectors have a magnitude and a direction.  Distance is a scalar quantity.  Displacement is a vector quantity.

Speed and Velocity  In English, the words ‘speed’ and ‘velocity’ are often used interchangeably to mean the same thing.  In Physics, these words have two different meanings, because ‘speed’ is actually a scalar quantity and ‘velocity’ is actually a vector quantity.

Speed and Velocity SpeedVelocity Scalar quantityVector quantity Example: 3 m/sExample: 3 m/s [North] Speed = v

Speed and Velocity SpeedVelocity

Uniform Motion  Uniform motion is what we have when velocity is constant. Answer True / False: An object moving at 3m/s straight across the room has uniform motion An object moving at 3m/s in a circle has uniform motion An object moving straight across the room but slowing down has uniform motion

Uniform Motion  Uniform motion is what we have when velocity is constant. Answer True / False: T An object moving at 3m/s straight across the room has uniform motion F An object moving at 3m/s in a circle has uniform motion F An object moving straight across the room but slowing down has uniform motion

Uniform Motion  Any change in speed or direction results in non-uniform motion.  Most motion is non-uniform  Non-Uniform motion = accelerated motion  Instantaneous velocity or instantaneous acceleration are the exact values of each in that instant. For uniformly accelerated motion, the instantaneous acceleration equals the average acceleration at any point.

Acceleration

 Negative Acceleration:  An object that is slowing down could be said to be decelerating 2 m/s 2 [North] or acceleration -2m/s 2 [South]. These are equivalent.

Acceleration due to Gravity  Question: Do all objects fall to the earth at the same rate? Your response: Yes / No

Demonstration  If we drop a textbook and a piece of paper at the same time, from the same height, will they fall at the same rate or different rates?  Your response: …..  Why you think so: ….

Demonstration  If we change things slightly….  What did we observe  Conclusion:

Demonstration  If we change things slightly….  What did we observe  Conclusion: Things fall to the earth at the same rate (with no air resistance). (This is because gravity affects all things the same way).

Example 1 A dog is walking down the street. He walks 30m [North] and then 40 m [West]. If it takes him 40 seconds to complete this trip, what is his average speed? What is his average velocity?

Example 2 When a ball is thrown upward, it experiences a downward acceleration of 9.8m/s 2 [down] (neglecting air resistance). With what velocity must a ball leave the person’s hand in order to go up 2.2 seconds before reaching its maximum height and stopping?

Homework  Complete the following questions:  Pg. 20 # 1-3,  Pg. 24 # 1 - 3