Pressure and Density

What is “pressure”, what is “density”, and how do we measure them?

Who contributed to our current ideas and theories about pressure?

Where can we see pressure measured on a daily basis?

Important Questions

In its simplest form, pressure is a force applied over a specific area.

Remember: ◦ Force is a push or pull (measured in Newtons)

Therefore, the equation for pressure is:◦ Pressure = Force / Area

What Is Pressure?

Units For Pressure English Units

◦ psi (pounds per square inch)

◦ psf (pounds per square foot)

Metric (S.I.) Units Pascal (pa) Atmosphere (atm) Bar (bar)

Like most measurements in physics, they are named after the scientist who “discovered” it.

Blaise Pascal was a French scientist and Mathematician from the 1600’s. His work included a hydraulic press and mechanical calculator. He named the units for pressure after himself while working with the hydraulic press. His mechanical calculator is also named after himself, the Pascaline.

Why Do We Measure Pressure In “Pascals”?

Where do we see pressure regularly?◦ Some examples include:

Tire pressure (measured in psi) Pistons in a car engine Blood pressure Supersoaker Water Gun

Examples of Pressure

Density is defined as “mass per unit volume”

Designated by the Greek letter “rho”: ρ More dense objects will sink, while less

dense objects will float (both in air and in liquid)

This explains why helium floats in air, because helium is less dense.

This also explains why lead sinkers sink in water, because they are more dense than the water.

Density

Which do you think is more dense: the yellow liquid or the red liquid? Why?

The equation for density is:◦ ρ = mass/volume◦ The units for ρ are [units for mass]/[units for

volume] Examples include:

Kg/m^3 g/mL Kg/mL

Calculating Density

Slide 6 Stethoscope: blog.timesunion.com Slide 6 Tire Pressure: gadgetrivia.com Slide 6 Pistons: dichotomistic.com Slide 6 Super Soaker: shoponline2011.com Slide 8: apartmenttherapy.com

Picture Credits