Final answer:
DNA moves down the gel towards the positive side because it is negatively charged and is attracted to the positive electrode. Smaller DNA molecules can travel faster through the gel due to less friction.
Step-by-step explanation:
DNA moves down the gel in a gel box towards the positive side because DNA has a net negative charge and is strongly attracted to the positive electrode. Gel electrophoresis is a technique used to separate molecules based on size and charge. Smaller DNA molecules are able to travel faster through the gel because they experience less friction as they migrate through the gel matrix.