1 Intro to Analysis of Motion By: Mike Maloney

2 What is Kinematics? Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs, and equations. The goal of any study of kinematics is to develop sophisticated mental models which serve to describe (and ultimately, explain) the motion of real-world objects. Or in normal human words, it is describing how a s#!t load of stuff moves in as many ways as possible so we can understand the world better.

3 How can we describe Motion? Let’s say Homer is sitting on my desk. Everyone but you closes their eyes and when they open them Homer is now on a different desk. How could you describe to the rest of the class the motion of Homer you observed? What terms could you use? What different ways could you describe it? Let’s use InterLace to discuss it.InterLace

4 Distance vs. Displacement We usually call the movement of an object its distance traveled. In the physics world, we have two words that describe the amount of movement of an object  Distance  Displacement We will learn how they are different next chapter. For now, we will use displacement, which is your change in position. Now lets try to describe Homer’s motion.

5 Displacement (change in position) Let’s call your position “s”. How might you write change in position?  Hint think to chemistry or lines in math class? We can use delta (  ), which means change  Displacement (change in position) is written as  s How can you change your position?  Go forward  Go backward  Go Sideways, or up, or down, …  How can we tell the difference?

6 Displacement (  x) That is what + and – is for. +  s means you have moved in the positive direction. -  s means you have moved in the opposite direction. SPECIAL NOTE: In real life what you call forward or backward or positive or negative direction is completely arbitrary. As long as you are consistent, and forward is opposite backward, and positive is opposite negative direction it does not matter.

7 Velocity (v) Another way to describe motion is to combine displacement and time. If we use time to determine how fast an object can change position, and fine the time rate of change in position, we get something called speed or more accurately velocity. Rate is something that comes up again and again in physics. So … what does it mean? It is just how much something changes something else does. For example …  How much money you earn per week  How many shots you make per game  How many times I roll my eyes per class

8 Velocity (v) Since you can move forward or backward, we need a way to describe this in terms of velocity. Any ideas? Right, we use + and – again. + velocity (+v) means you are moving in whatever you called the positive direction, or you have a positive change in position over time. - velocity (-v) means you are moving in the negative direction or you have a negative change in position over time.

9 Beyond Velocity So now we know that position can change (displacement) and the time rate at which it changes is called velocity. Is this enough to completely describe Homer? Velocity is not always constant. When you step on the gas pedal in a car the car speeds up, the velocity increases. Stepping on the brake does the opposite, the velocity decreases, the car slows down. So we need a way to describe this too.

10 Acceleration (a) Just as velocity is the time rate of change of displacement, acceleration [a] is the time rate of change of velocity. Acceleration can be positive [+] or negative [-].  A positive [+] acceleration means increasing + velocity  A negative [-] means decreasing + velocity Hmmm. Is there any other way we could get a + acceleration?  Ahh! It is a little tricky, but we could also use a decreasing (–) velocity. Anyone know how or why?

11 How can we diagram motion Now that we know some terms that describe motion, how can we diagram it or graphically describe it? Motion Diagrams (Interlace || Java)Interlace Java Graphs (with Usain Bolt)with Usain Bolt Graphing Challenge (doc | game)doc game

12 The 4 ways to describe Motion Words Variables and Equations Graphs Motion Diagrams