Hello!
3. How does temperature affect a football players performance?
Independent Variable: Temperature
Temperature is the independent variable because that is what you are testing.
Dependent Variable: Points scored in game
Since you are attempting to measure how well football players do in different climates, you must measure their scores.
Constants: Uniform, field played in, and ball used
If you use a different uniform, field, or ball, then the data is obviously going to be inconsistent.
Hypothesis: If football players are in colder climates, then they perform better during games.
This is quite self-explanatory: just use the latter data points to craft your hypothesis. Keep in mind that a hypothesis should NEVER be a question!
I hope I helped! :-)