Measurement and Units

Density

Density

Mould a piece of plasticine so that it will float in water when dropped into it

Density

Objectives: Define density Calculate density of an object Predict whether objects will float or sink

Density

Density is defined as the mass per unit volume of object.

SI unit: kg/m3

Other units: g/cm3

mD=

v

Density

The value of D increases when V decreases or m increases

The value of D decreases when V increases or m decreases

mD=

v

Calculating Density

ExampleThe density of water is 1000kg/m3. What is the mass of water needed to fill a tank of that has a dimension of 3 x 2 x 1?

3m

2m

1m

Calculating Density

mD =

vm

1000= (3x2x1)

m = 6000kg

Mass, m, of water is 6000kg

Floating and Sinking

Comparing densities allow us to determine whether objects float or sink.

Density

Matter is anything that occupies space and has mass. Hence all matter has density.

Matter will sink or float in each other depending on their density.

Knowing density allows us to separate objects

Density

Why does a 1000kg log floats on water while a 10g steel screw sinks in water?

•Floating and sinking depends on density and not mass alone.

•The density of the log is smaller than that of water. (Log has big volume)

•The density of the steel screw is greater than that of water. (Steel screw has small volume)

Density

Density in Application

Conclusion

Density is defined as the ratio of mass to volume.

Floating and sinking depends on density. Different material have different densities.