Keeping the "Display Forces" and "Two Blocks" options turned off:

• Pick up the green block and drop in in the water. What happens? Look at the water level - what happens when you take the block out of the water? When you put it back in?
  
  
• Try adjusting the time slider control. What does it do? How many positions does it have? Why might the two left most positions be very useful?
  
  
• Try adjusting the mass slider control. How does the mass of a block affect its density? When you pick up the block and drop it in the water, how does the mass affect what happens?
  
  
• Set the mass control slider to somewhere near the middle. Now try adjusting the size slider control. When you pick up the block and drop it in the water now, how does the size affect what happens? Freeze time and put the block all the way under the water. Now adjust the size again - what happens to the water level? Why do you think that happens?
  
  
• Try adjusting both the mass and size sliders to get the block to just barely float. This can be tricky! If you get it just right, then you'll be able to take the block, put it completely under the water, and it won't rise or sink - it will just sit there. This is called neutral buoyancy. How many different settings of mass and size can you come up with so that you achieve neutral buoyancy? What does the density have to do with it, if anything?
  
  
• Now that you know what neutral buoyancy is, there are two other terms you should know. When the block's mass and size are set so that the block rises to the surface to float, that is called positive buoyancy. And when the mass and size cause it to sink to the bottom, that's called negative buoyancy. What does the density of the block have to do with positive and negative buoyancy?
  
  

Turn on the "Two Blocks" option, but keep the "Display Forces" option off:

• Each time you click on a block, the sliders change to adjust that blocks mass and size. Try it out. Now, can you set it up so that the blocks are about the same size, but one sinks and the other floats? How do you do it?
  
  
• Now set it up so that the blocks have about the same mass, but one sinks and the other rises. What did you have to do this time?
  
  
• If you look at the "Force Legend" area, you will see two arrows, which represent forces. As you can see, there are primarily two forces acting on each of these blocks - the buoyant force and the weight. Keeping the "Display Forces" option turned off, answer two questions. How do you think the mass of the blocks affect these forces? How does the size affect the forces?
  
  

Turn on the "Two Blocks" option and turn on the "Display Forces" option:

• How does the mass affect the weight? Is the weight different when the block is in or out of the water?
  
  
• How does the size affect the buoyant force? Is the buoyant force different when the block is in or out of the water?
  
  
• What causes the block to rise or sink, in terms of the weight and buoyant force? Why does the block always fall when it is out of the water? Why does is fall more slowly or even rise up when it goes under the water?
  
  
• Try to get the weight and buoyant forces exactly equal to each other. What happens? What is the density of the block when these forces are equal? Try placing the block anywhere that is completely under the water. Now try placing it so that a little bit of it stick out above the surface. What is the difference between these two setups and why does it happen? (Look and the forces!)