Boats can float because of buoyancy. At the same time they are pulled down by the force of their own weight (caused by gravity) they are pushed up by the buoyant force, which is equal to the weight of the volume of water they displace.

Learning Stages Fill a tub or bowl with water and collect items made from different materials, some that you know will float and some that will sink. Some examples are: plastic spoon, plastic toys, wooden boat, wooden block, pencil, stainless steel spoon, nail and paperclip.

The force of gravity yields a downward force and a buoyancy force yields an upward force. If the gravitational force is less than the buoyancy force then the object floats (a boat), otherwise it sinks (a rock). That is, if an object weighs less than the amount of water it displaces then it floats otherwise it sinks.

Paper boats float based on the principle of buoyancy, which is the same principle that explains why anything floats. In effect, the water pushes up against the boat with more force than the boat pushes down. This keeps it above the surface.

It will remain submerged in the fluid, but it will neither sink nor float. An object with a higher average density than the fluid has less buoyancy than weight and it will sink.

If the object is denser than water it is more massive than the water that it displaces. This means that the object experiences greater gravitational force than the water and so sinks.

Objects are made up of very tiny molecules. Objects with tightly packed molecules are more dense than those where the molecules are spread out. Density plays a part in why some things float and some sink. Objects that are more dense than water sink and those less dense float.

Key Concepts The density of an object determines whether it will float or sink in another substance. An object will float if it is less dense than the liquid it is placed in. An object will sink if it is more dense than the liquid it is placed in.

A penny, paperclip, or button sank because the materials they are made of (metal for a paperclip and penny, plastic for a button) had more density than water. (Their molecules are closer together than water molecules are.) A cork, piece of wood, or Styrofoam floated because those materials have less density than water.

Objects like apples, wood, and sponges are less dense than water. They will float. Many hollow things like empty bottles, balls, and balloons will also float. That’s because air is less dense than water.

There are seven major materials used to make sinks:

• Stainless Steel.
• Composite.
• Cast Iron.
• Porcelain.
• Copper.
• Glass.
• Natural Stone – Travertine.
• Natural Stone – Granite.

Stylish, Stain-Resistant, or Both: Which Type of Kitchen Sink Is Right for You?

• Stainless Steel. Best for: All types of use; kitchens with stone or granite countertops.
• Copper. Best for: All types of use; farmhouse-style kitchens.
• Enamel.
• Fireclay.
• Solid Surface.
• Stone.
• Composite.