what are examples of the conflict person vs. unknown in Roll of Thunder

Person vs. Unknown- The families that joined in the boycott had no idea what the end result would be. Pooling money and seeking credit to purchase large stores of goods was risky.

Person vs Machine- Mr Logan and the wagon wheel is a great example of man against machine. The fact that someone tampered with the wagon put him in great danger, and his inability to get it all working quickly enough led to his leg being run over. He couldn't get home without the wagon, and the men who'd tampered with the wheel didn't want him to get home at all.

Person vs Society- I think the greatest example of this is shown in David Logan's sacrifice of his own cotton (he set it on fire) to distract the landowners enough that he could save TJ from being hung for murder. With this selfless act, Mr. Logan goes far beyond what anyone would expect to fight against the injustice of the society he lives in.