1

Air Pressure 2

One factor that greatly affects the weather is air pressure 3 Vocabulary: air pressure The push of air on Earth

4 Air is made of many gases These gasses are made of tiny particles

5 The particles have weight and push down on Earth The push of air on Earth is called air pressure

6 Air pressure is changed by temperature The picture shows how temperature changes the pressure of air

7 When air is heated, the particles of air move apart and upward

8 When air is cooled, the particles move closer together and stay low

9 The cold air is heavier and has more pressure Cold air has more particles of air than the warm air

Air pressure is different in warm and cold places 10 Warm Cold

11 The particles of air above a warm place begin to spread out The warm air becomes light and starts to rise

12 As warm air rises, it has less pressure rising air forms a low-pressure area, called a low

13 Vocabulary: low An area of low pressure formed when warm air rises

14 Cold air is heavier than warm air because the particles are packed tightly together

15 Falling cold air forms a high-pressure area, called a high Since cold air is heavier than warm air, it falls to the ground

16 Vocabulary: high An area of high pressure formed when cold air falls to the ground

17 The greater the difference in pressure between the areas, the stronger the wind will be Vocabulary: wind The movement of air from a high- pressure area to a low-pressure area

18 People who study weather measure the air pressure every day with a barometer Vocabulary: barometer An instrument that measures air pressure