Good Riddles

Question: What are the strongest creatures in the ocean?

Question: Why are pianos hard to open?

Question: What did the tie say to the hat?

Question: If green means go, yellow means slow down or caution, and red means stop. Why can't traffic lights go when they turn to green?

Question: I am full of light but left in the dark. I have a temper that pushes my single sibling. I have many friends very far away and I disappear in the light when it is my sibling's turn to push me back. What am I?