A contact force is a force in which and object comes in contact with a another object. A non-contact force, is a force is an object applied by another body. (A good example of a non-contact force is gravity)
When you are asked a question like this, you can always ask yourself this question. Can I change it back after this change? For example, if you are burning wood, you cannot bring it back to wood after you burn it, therefore, it is a chemical change. However, if you boil and evaporate water, you can make the water condense again back into its liquid form. In this case, you cannot bring the tomato back to its raw state. Therefore, cooking raw tomatoes is a chemical change.
Answer:
A lower ph is always more acidic, due to the increased concentration of hydrogen ions in the solution/substance.
A ph of 3 is 100 times more acidic than a pH of 5, and this is due to the increments on the scale.