Forces change the motion of an object.
This concept can be taught with Minecarts. Students can build three different tracks for Minecarts:
Track 1: Straight and flat (20 pieces of track)
Track 2: Uphill (20 pieces of track)
Track 3: Downhill (20 pieces of track)
Students can then discuss how the minecraft traveled differently on all three tracks and what forces may have been acting on the minecart to make it move the way it did.
The lesson can be extended by having students discuss the amount of track that would be needed to get to the same location for each type of track.