Thinking about air resistance using tennis balls!

Let's think about air resistance and friction a little bit more. Think about how we defined air resistance before: as a backwards force caused by bumping into air molecules. Therefore, if we bump into more air molecules, this force will be stronger. Based on this defintion, can you think of some quantities that might be proportion to air resistance? You can test this in practice: Try throwing a gold ball and tennis ball, whcih roughy have the same weight. Can you throw one of them further or faster? Why?