Question: For the following sentences:

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> * He threw the book *at* the floor.
> * He threw the book *on* the floor.
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I know the book hit the floor in both sentences but which one is more commonly used and also what's the difference between 'at' and 'on'? Do we acknowledge the exact position from 'at'?

Answer: 
We typically use *at* when talking about an upright target:

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> He threw the book **at** the dog.  
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>  The judge threw the book **at** her.  
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>  I threw my food **at** the wall.
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If the target is flat, we typically say *on* instead:

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> I spilled it **on** the floor.  
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>  I dropped my things **on** the table after school.
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I believe the word "on" also implies a final resting place. If you throw your book on the floor, and don't implicitly tell us where it ended up, we will immediately assume it's still on the floor. Similarly, if I "throw my clothes at the floor" on my way to the shower, it implies that I really don't care where they landed; they may have ended up on the back of a chair or on the dog laying in the corner. The emphasis is on that shower.