# Equation for density and why things sink or float. Part 2

WHAT IS THE EQUATION FOR DENSITY AND WHY DO SOME OBJECTS FLOAT IN WATER?

### Contributed by: Margaret V. Date of Publication: 9/30/11

The formula for density is d= m/v. The key is: d = density, m = mass and v = volume. The objects’ mass can vary which changes density between multiple objects if not duplicates. Some objects if not multiples of each other can have same or similar masses. An example is that my brother and I are 5 years apart, so his mass would be greater than mine but if I was to measure myself and a friend my age, we would have similar or same masses. More objects have the density of solid materials than liquid – like materials. The rule breaker is ice which has a lighter density than water.
Density makes objects float. A stick floats because it has a very light mass and a metal coin sinks because it has a very heavy mass. Using a triple beam balance for measuring mass is an excellent technique. We used a triple beam balance a couple weeks ago to measure the mass of a plastic block and a metal block. The metal was heavier than the plastic. If you used numbers to describe sinking and floating, water would be 1, anything higher than 1 would sink and anything lower than 1 would float. The Titanic was an amazing ship that nobody thought would sink. It sank a few days later after hitting an iceberg. It now lies at the bottom of the Atlantic Ocean. How do boats float when they are so heavy? Boats float of buoyancy. Buoyancy is the force or act of pushing up. When buoyancy acts as gravity pulls down, boats and other objects can float no matter how much it weighs. With passengers on board, the Titanic weighed about 45,500 tons or 91,000,000 pounds, yet it still floated because of buoyant and gravitational forces. But, then why does a metal coin sink? Ships are designed to move water in a certain way. If you have seen a picture of a boat, it probably has a sharp/pointed end called the bow, which is shaped for cutting water. Metal coins simple aren’t made to float.

QUESTIONS
1. Why do boats float?
1. Because of buoyancy and shape
2. Because of gravity and shape
3. Because of gravity and buoyancy
2. What was the weight of the Titanic?
1. 45,612 tons
2. 91,000,000 pounds
3. Both
3. What is the formula for density?
1. D= m/v
2. V=d/m
3. M= v/d
4. True or False- More objects have density of liquid materials than solids.
1. True
2. False

1. 3
2. 2
3. 14. 1

1 Why some objects sink and float

2 This is the formula for density

GLOSSARY
The Definitions for density
1) The state or quality of being dense; compactness; closely set or crowded condition.
2) Mass per unit volume
The Definition(s) for key words
Floating- being buoyed up on water or other liquid
Water- a transparent or see through, odorless, tasteless liquid

CITATIONS
Dictionary.com. "density" http://dictionary.reference.com/browse/density Dictionary.com, 2011. Web. 26 September, 2011.
Dictionary.com. "floating" http://dictionary.reference.com/browse/floating Dictionary.com, 2011. Web. 26 September, 2011.
Dictionary.com. "water" http://dictionary.reference.com/browse/Water Dictionary.com, 2011. Web. 26 September, 2011.
Image 9/21/11 http://leifchemistry.blogspot.com/2010/11/lab-2-e.html Web
Kahan, Peter. Sinking and Floating Motion, Energy and Force Student Edition. Needham, Mass. Prentice Hall, 2000. Print.
Wikianswers "How can a metal boat float when a coin sinks”? http://wiki.answers.com/Q/How_can_a_metal_boat_float_when_coins_sink#ixzz1Z0ZthkqW Wikianswers, 2011. Web. 26 September, 2011.