Exploring Reference Points Depending on the reference point you choose, the same object can seem to be
moving or standing still. Furthermore, even if an object seems moving from two
different reference points, observers at those points might disagree about its
speed and direction.

Here is a simple example: In the diagram below, a crow is flying along at a con-
stant speed, carrying a ball. Suddenly, it accidentally drops the ball and watches

it fall. The diagram shows the position of the crow and the ball at five points in
time, one second apart. A person standing still on the ground also watches the
ball fall.

Answer the following questions on a separate sheet of paper.
1. From the reference point of the crow, in what direction is the ball falling? Does
it appear to follow a curved or straight path?
2. How many seconds does it take the ball to fall to the ground?

3. The sides of the grid squares in the diagram are 5 meters long. Using this, cal-
culate the average speed of the ball during its fall from the point of view of the

crow. About how fast was it traveling during the last second of its fall from this
perspective?
4. From the reference point of the person on the ground, does the ball appear to
fall in a straight or curved path?