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Now is the time to read Chap 1 of your textbook! Then come back to read the next two pages.

Representing the motion of the rocket car

Let us apply the concepts of motion you saw in Chap 1. Knight to the rocket car motion.

For the moment we are working in one dimension so imagine we live in a Universe that is a single line. You can only move right/left (or up/down say).

We can denote our position on this line using a label x . We can call our home the x=0 spot and everything to the right is positive x values while everything to the left is negative x value. To prevent confusions, we will almost always take positive x to be to the right.

In the video below, the motion of the rocket-car is in a straight line. The rocket started from rest and kept moving faster and faster from left to right.

To represent this motion, we will first imagine that the rocket and me are represented by a single point (imagine that we have no size). We can then do a series of snapshots photos of where the rocket car is at equal intervals of time (every second, for example).

This is the motion diagram for the rocket car motion and this figure is very informative. It tells us the position of the rocket car at different instant of time. Since the interval of times are equal, we see that the rocket car traveled a bigger distance between time 4 and time 5 than it did between time 1 and time 2. The speed was greater toward the end than it was at the beginning. The rocket car was accelerating .

Graphs

In science, we often like to use graphs to represent and visualize information. A graph is an abstract and conventional way of presenting scientific information to an audience. A common graph has two axes or more. For example, here is a position-versus-time graph.

Hint: When you see a graph for the first time, start by determining what the vertical and horizontal axis represent!

So, for example we could decide to do a position-versus-time graph for the rocket car. To do that, we put points on the graph where vertical heights represent position and horizontal distance represents time. To help me do this correctly, I can rotate the rocket motion diagram from horizontal to vertical. Then I separate each point at equal horizontal spacing for each time. This gives the following graph.

We can connect the dots by a line that goes through all of them. The end result is

Note that the shape of the graph has nothing to do with what the actual motion looked like. The motion was on a line, the graph is in two dimensions. The graph is a representation of the motion (position and time together).