https://youtu.be/LI7D6inks08
PHYS 1101: Lecture Nine, Part One
Welcome to Lecture 9. This material will cover the last section in Chapter 3 that we need to do before our first exam. And that material has to do with studying projectile motion. This is just a special case of two dimensional motion where objects are going to follow a curved trajectory.
We’re going to start as usual with our first quiz question. If the majority of the class answers correctly, I’ll give everyone five points for this question. Otherwise, one point.
Which of these examples, a through d, represents constant non-zero acceleration? Non-zero acceleration means whatever the acceleration vector is for the problem, this would be from the start to the finish. The whole duration, start to the finish. Start to the finish. Wherever that vector is, it has to stay the same length and the same orientation the whole duration of the problem. That’s what a non-zero acceleration would be.
And remember, when I draw an arrow like this for the acceleration, you can equivalently think of that as representing the change in velocity, the difference between any two adjacent velocity vectors on these diagrams.
So the start to the finish is clear for all of these problems except perhaps this circular motion one. Won’t you consider this first spot that you see here at the top, at 12 o’clock, as being the start and then the end would be after one cycle.
I have another bonus quiz question for you here for this lecture. This is Question 2. And again, I’ll give everyone in the class plus five if the majority of you get it right otherwise, plus one.
And this is just a question very much like you’ll find on the exam that’s coming up. It’s back to one dimensional motion, as evidenced by the fact that this objects following a straight path, straight line. And which of these motion diagrams represents a negative velocity and a negative acceleration, given this is the positive x direction?