Density & pressure

What is the formula linking density, mass & volume?

Density = mass ÷ volume

ρ = m ÷ v

The units for density are…

kg/m³ or g/cm³

To find the density of a regularly shaped solid…

Measure the mass of the solid with a top pan balance

Measure the dimensions of the solid with a ruler & then calculate its volume by l × w × h

Calculate the density of the solid by ρ = m ÷ v

To find the density of an irregularly shaped solid…

Measure the mass of the solid with a top pan balance

Fill a Eureka can with water so that it is level with the bottom of the pipe & place a measuring cylinder under the pipe

Put the irregular solid into the Eureka can & some of the water will be displaced into the measuring cylinder

Measure the volume of displaced water (this is the volume of the solid)

Calculate the density of the solid by ρ = m ÷ v

To find the density of a liquid…

Put a measuring cylinder on a top pan balance & record its mass

Fill the measuring cylinder with the liquid & the record the new mass

Calculate the mass of the liquid by final mass of measuring cylinder - initial mass of measuring cylinder

Measure the volume of the liquid with the measuring cylinder (read it at eye level to avoid parallax error)

Calculate the density of the solid by ρ = m ÷ v

What is the formula linking pressure, force & area?

Pressure = force ÷ area

P = F ÷ A

The units for pressure are…

Pascals (Pa)

The pressure at a point in a fluid at rest acts…

Equally in all directions & causes a force at right angles to any surface

Pressure in a fluid is created from…

The movement of particles as they collide with a surface

The pressure beneath a liquid surface increases with…

Depth → the deeper in the fluid the more particles above the point, hence the greater their weight

The density of the liquid → fluids with higher density have more particles per unit of volume, hence greater weight

The gravitational field strength → weight depends on gravitational field strength

What is the formula linking pressure difference, height, density & gravitational field strength?

Pressure difference = height × density × gravitational field strength

p = h × ρ × g