• NOVA teaches about boyancy with a "Boat in the Pool" brain teaser.Big Boat, Little Boat image by Aubrey Thompson from Fotolia.com
  
  According to a study published in the Journal of the American Medical Association, cognitive training helps slow mental decline in adults. Use brain teasers to exercise your mind.
  
  

Riddles

• You check out a book from the library that has the foreword after the epilogue, the end in the first half of the book and the index before the introduction. What is the book?
  
  Answer: A dictionary
  
  A man is inside a cabin in the country. All cabin walls inside face south and are made of wood. A bear walks by the window. What color is he?
  
  Answer: If all walls face south, the only possible location is the North Pole, so the bear is a polar bear, and he is white.
  
  I'm part of the bird that's not in the sky. I can swim in the ocean and yet remain dry. What am I?
  
  Answer: The shadow
  
  

Word and Letter Play

• NOVA poses questions to help students better understand buoyancy. A toy submarine (made of steel) floats in a bathtub. It weighs 1 lb. When completely submerged, it displaces 2 lbs. of water. What could you do to cause the sub to sink to the bottom of the tub?
  
  Answer: The sub needs to weigh more than the maximum weight it can displace. You'd need to slightly more than 1 lb. of weight so that the sub weighs just over 2 lbs.
  
  A girl sits in a boat floating in a pool. She picks up a rock in the boat and tosses it in the pool. The rock sinks to the bottom. No water leaves the pool from the splash the rock makes. Does the pool's water level rise, lower or stay the same?
  
  Answer: The water level lowers. When the rock is in the boat, it displaces its total weight. So, if the rock weighs 2 lbs., the boat is 2 lbs. heavier. When the rock is sitting at the bottom of the pool, it displaces its volume. The rock displaces more water when it's in the boat than when it's in the water, so the water level lowers when the rock is in the water.
  
  

Plays on Words and Letters

• If you start with the number 1 and use just whole numbers, how far can you count before you use the letter "a" to spell a number?
  
  Answer: One thousand
  
  For each of the following expressions, rearrange the letters to make a new expression. Hint: The first phrase is a two-word phrase, the second is a three-word phase.
  
  no city dust here
  
  dose ease thirst
  
  Answer:
  
  the countryside
  
  the desert oasis