difference in meaning

Can you tell me the difference in meaning betwenn the following pairs of sentences?

1. If I had the money, I'd buy a new car.
If I have the money, I'll buy a new car.

2. The house was very isolated.
The house was very secluded.

3. Give me a hand with this bag, will you?
Could you give me a hand with this bag, please?

Thank you for you help.

[Tdol]

1- In the first sentence, the person doesn't have the money. In the second, they may not have it now, but they thin k they may get it.
2- 'isolated' may carry a slightly negative connotation- if you wanted to be in a city, you'd be more likely to use the first. If you love your privacy, then 'secluded' sounds good.
3- Familiarity- say the first to a friend and the second to someone you know less well or don't have a close social relationship with.

[critic72]

1. The former sentence is generally called a subjunctive form. You need to refer to this part in any grammar book. It looks like a past tense, but you should interpret the sentence as if it were a present tense.

3. As Tdol's explanation suggests, the latter sentence sounds much more polite than the former.

In addition, a sentence like "Can you give me a hand with this bag?" sounds less rude than the former but less polite than the latter.