Intro to Kinematics

1. Intro to Kinematics

2. Scalars and Vectors • We will come across and use two different 'kinds' of measurements as we study physics: 1. Scalars 2. Vectors • Because these two measurements have fundamental differences we must: a) be able to distinguish between them b) follow different rules when using them

3. Scalars • Scalar measurements tell us only the magnitude of the quantity being measured - Scalars numbers tell us "how many" ex) 5 m (distance, s) 10 s (time, Δt) 100 kmh-1 (speed, v) • The symbols used to denote scalars are usually letters  • scalars can be added, subtracted, multiplied, divided, etc. just as ‘regular’ numbers can be ('regular' numbers are scalars…)

4. Vectors • Vector measurements tell us the magnitude of the quantity being measured and the direction over which it is be measured • Vector numbers tell us "how many" and "where" ex) 5 m [left] (displacement, ) 100 kmh-1 [east] (velocity, ) • The symbols used to denote vectors are usually letters with a small arrow above them  • Vectors can be added, subtracted, divided, etc. but we must modify the process used according to the direction attached to the quantity • You CAN'T treat vectors like 'regular' numbers! • we will learn how to add vectors that exist in a single dimension in this course…

5. Intro to Kinematics • before we can hope to understand the physics of the moving world, we need to define some important terms used in this branch of physics • the branch of physics that deals with motion is called kinematics • as it turns out, our universe behaves in a very predictable fashion • it appears to obey some very simple rules that can be summarized in the form of mathematical equations • before we can understand and use these rules, we need to be able to measure and define a few fundamental quantities:

6. Distance and Displacement • these expressions will appear in a few of the kinematics equations we will be using • Distance (s): • a scalar quantity that measures the space an object moves through our three dimensional world • is equal to the sum of the distances moved in any and all spatial dimensions/directions • measured in SI base units called metres(m)

7. Displacement ( ): • a vector quantity that measures the space an object moves through our three dimensional world • is equal to the vector sum of the distances moved in any and all spatial dimensions/directions • measures a change in position (ie: the distance between the starting point and the ending point) • measured in SI base units called metres (m)

8. Example: An MMC student walks 200 m [E] to get to school. After school this same student walks 50 m [W] to get to work. • What is the total distance this student walked? • What is the displacement of the student?

10. Time (Δt) • whenever objects move through spatial dimensions, they are also moving through the dimension of time • unlike spatial dimensions, all physical objects can only move in one direction through time: forward! • during our study of kinematics we will see that the kinematics equations require that objects moves through time • this movement in the time dimension is represented as the as ‘change in time” or Δt in equations • expressed in SI base units called seconds (s)

11. Speed and Velocity • Speed (v): • a scalar quantity that measures how far an object travels (distance) in a given time • expressed in SI base units called metres per second (ms-1) • Velocity ( ): • a vector quantity that measures the displacement of an object in a given time • expressed in SI base units called metres per second (ms-1)

12. Different “kinds” of Speed/Velocity u v

13. Acceleration ( ) • an object experiences an acceleration whenever it’s velocity changes • acceleration is equivalent to the rate of change of velocity • if an object’s speed remains constant (ie: doesn’t change) the object is NOT accelerating! • expressed in base units called metres per second2 (ms-2) • Convention: • if velocity “increases”, object is said to accelerate • if velocity “decrease”, object is said to decelerate