What happened when the wheel was invented?

It is always ahead of me yet I can never see it. What is it?

Speaking of rivers, a man calls his dog from the opposite side of the river. The dog crosses the river without getting wet, and without using a bridge or boat. How?

How can you leave a room with two legs and return with six legs?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?

A train leaves from point A for point B at 80 mph. After half an hour, another train leaves from point B for point A at 60 mph.

Which of the trains will be farther from point A when they meet ?

Two guards were guarding the camp.Guard-1 was looking towards the south to make sure no threat is coming from the road.Guard-2 was looking at the north to make sure no threat is coming from the top. Suddenly Guard-1 ask the Guard-2 why he is smiling?How Guard-1 knows that Guard-2 is smiling?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

I can be cracked, made, told, and played. What am I?

What can you catch but never throw?