Make a tickertape by dropping an object attached to the tape. Use different sized objects. Divide the tape into sections of 5 dots. Compare two sections, one near the start and one near the end. Measure the distance travelled in this section, then divide by 0.1s to find the speed in this section. Work out the speed in the second section. Work out the change in speed, and divide it by the change in time between the two sections.