DO NOW: EDMODO

HAVE OUT LAB TO HAND IN

PRESSURE

PRESSURE The force applied divided by the

surface area Pressure = Force/Area Force (or weight) of an object

depends on its mass and the pull of gravity

Area – the total surface of an objectLength (m) x width (m)Unit used is meter squared (m2)

THE RELATIONSHIP…

As force increases, pressure also increases – directly proportional

As area increases, pressure decreases – indirectly proportional

IF SOMEONE STEPPED ON YOUR FOOT WEARING THESE SHOES… WHAT WOULD HURT MORE?

Why???

Just like pressure is exerted on your foot- gas molecules exert pressure on things too.

Pressure can be measured in many different units:

Inches of mercuryPounds per square inch (psi)Millimeters of mercury (mmHg)

Atmospheres (atm)

That’s a lot of different units for one thing!!

HOW DO SCIENTISTS COMMUNICATE?

Certain units are used in scientific measurements

International System of Units (SI) – lets scientists all over the world to communicate with each other.

Chart

SI UNIT CHART

HOW DO SCIENTISTS COMMUNICATE?

Certain units are used in scientific measurements

International System of Units (SI) – lets scientists all over the world to communicate with each other.

Chart

There are 2 different “kinds” of units:

- Base Units- Derived Units

Base Units – There are 7!!basic physical measurements (units in the metric system)

Ex: mass and length

Derived units – Must be figured out mathematically

Ex: area, force, volume and pressure

UNITS FOR FORCE AND PRESSURE

Force is measured in Newtons (N) A bar of soap pushes down with

about 1N of force.

Pressure is measured in Pascals (Pa) Pascal (Pa) = N/m2

To find pressure need 2 things:1. Force (units = N)2. Area (units = m2)

CONCEPT CHECK:

Photo shows two bricks of the same mass lying on the ground. 1. Is each brick exerting the same total force on the ground? Explain.

2. Is each brick exerting the same pressure on the ground? Explain.

SAMPLE PROBLEM:

Determine the area of the brick on the right side of the photo in Figure 2.7.

The dimensions of the brick surface touching the ground are 9.3 cm × 5.5 cm.

** Remember we want to have the units in meters(m)! So we will need to convert cm m.