1. Density D = M / V 9-13-10

2. What is Density? Density – the amount of matter (mass) in an object per unit of volume In other words: How much stuff is packed into a given space.

3. How do we find an objects DENSITY? We need to know two things: – The objects mass (measured by scales and balances) – The objects volume (measured by MATH (L*W*H) or water displacement)

4. Mass Mass – how much matter (molecules) there is in an object Closely related to “weight” (mass and weight are equal on Earth only) but mass does not change no matter where in the universe the object is (weight changes based on gravitational fields) With modern technology finding mass is simple: Place the object on a scale Units of mass usually = GRAMS (g)

5. Volume Volume - The amount of space an object takes up Not quite as easy to calculate... A “cube-like” object’s volume can be found by the equation V = L*W*H (measured in cm) To calculate other shapes (which most things are) we need to measure how much water an object displaces

6. Displacement “displacement occurs when an object is immersed in a fluid, pushing it out of the way and taking its place. The volume of the fluid displaced can then be measured, as in the illustration, and from this the volume of the immersed object can be deduced (the volume of the immersed object will be equal to the volume of the displaced fluid).”

7. Displacement Simply measure the difference between water levels in a graduated cylinder. Draw a pic of a grad. cyl. below:

8. Putting it all together: DENSITY Now that we have mass and volume, we can easily calculate density. Since the definition of density is mass per unit of volume: – D = M/V or Density = Mass “divided by” Volume – Don’t forget units! Mass = grams, volume = ml or cm 3 – So density’s units are g/mL or g/cm 3

9. Lets try some examples! Clearly write out each problem so that you can refer back to them for examples when completing homework.