# Density, and Pressure

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A series of free Online High School Physics Video Lessons.

In this lesson, we will learn

• density
• elastic modulus
• bulk modulus
• liquid pressure

### Density

Density is the compactness of mass. Density is expressed mathematically as mass over volume and in physics is expressed using the units kg/m3.
Understanding how density relates the volume and mass of a substance.
Density
An experiment to calculate density.

Density problems:
A piece of granite rock has a mass 15.5 gram and a volume of 6.01 subic cm. What is its density?
Gold has a density of 19.3 g/cm3. If you have a gold bar with a volume of 44.9 cm3, what is its mass?
Isopropyl alcohol is a liquid with a density of 0.785 g/cm3. How much volume will be taken up by 50.0 grams of isopropyl alcohol?

### Elastic Modulus

Elastic modulus is a quantitative measure of how much something wants to return to its original shape and size. Generally it can be thought of as stress over strain. It can be calculated as applied pressure / fractional change in size. Young's Modulus is an elastic rod stretched one dimensionally, only expanding in length, which behaves like a spring and can be calculated using Hooke's Law.

### Bulk Modulus

Bulk modulus is a modulus associated with a volume strain, when a volume is compressed. The formula for bulk modulus is bulk modulus = - (pressure applied / fractional change in volume). Bulk modulus is related to elastic modulus.
How substances behave when their volume is compressed.

### Liquid Pressure

Liquid Pressure is the increase in pressure at increasing depths in a liquid. This pressure increases because the liquid at lower depths has to support all of the water above it. We calculate liquid pressure with the equation liquid pressure = density × acceleration due to g × depth in fluid.
How the pressure in liquids increases at greater depths.

Calculate the pressure knowing the height of a liquid using P = dgh.

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