You are conducting a physics demonstration where you need to slide a heavy block across a surface with minimal resistance. You decide to use a gas to reduce friction. Which of the following methods would be most effective in demonstrating the principles of reduced friction using gas?

The gas that comes out of the CO2 container spreads over the block and the surface, forming a thin layer that keeps them apart. Other options are incorrect because Oil makes the block slide faster, but it does not use a gas; A rough surface would give more bumps for the block to grab, so friction would grow, not shrink.