Scaffolded notes
Build the idea
Air has mass and pressure
Gas particles collide with surfaces and exert force. Air pressure is the force of air spread over an area. Near sea level, a typical pressure is about 1013 millibars, but it changes with altitude and weather systems.
Pressure trends are evidence
A rising barometer often accompanies approaching or strengthening high pressure and more stable conditions. Falling pressure can signal an approaching low-pressure system and increasing chances of clouds, wind, or precipitation. Pressure alone is not enough; meteorologists combine it with other evidence.
Tools answer different questions
A thermometer measures temperature, a barometer measures pressure, a hygrometer measures humidity, an anemometer measures wind speed, a wind vane shows the direction wind comes from, and a rain gauge measures liquid precipitation depth.
Stop and explain
Check your thinking
1. Which tool measures humidity?
Possible response: Hygrometer.
2. What does a falling pressure trend suggest?
Possible response: A low-pressure system or unsettled weather may be approaching, but other evidence is needed.
Interactive challenge
Try the science
Which observation is direct evidence that a low-pressure system may be approaching?
Before you leave
Exit ticket
Which two instruments would best test whether conditions are becoming windier and stormier?