I disappear the moment you say my name. What am I?

I have four legs in the morning, two at noon, and am strongest with three in the evening. What am I?

The more you take away from me, the bigger I become. What am I?

I weigh nothing, but you can see me. Put me in a bucket and I make it lighter. What am I?

The person who makes me doesn't need me. The person who buys me doesn't use me. The person who uses me never knows it. What am I?