This first assignment has two keys: #1 and #3. The inbetween is #2.
You are to draw 1 inbetween for each ball.
Begin first by flipping the drawings to see what is going on and where the drawing is coming from and where it's going to. Look at the two lines that represent a center line and an eye line for an understanding of the rotation of the sphere.
Place a blank sheet of paper over the two keys and lable it "2" in the lower right corner.
Start the drawing by loosely sketching the volume of the ball in the half way position. Decide on whether you're going to use a curved path of action or a straight one. Curved is the preferred line as things rarely move in straight lines unless they are mechanical in nature. "Inbetween flip" the drawings to see the action taking place and make sure the movement is correct and the volume is being maintained. Make any corrections before you move on.
Begin with either the eye line or the center line, it doesn't really matter which. Lightly sketch in the line and flip th drawings to see the motion. Make corrections and darken it in when you've settled on the final line. Now move on to the next sphere and repeat the process until you've finished all 4.
See my inbetweens