This activity explores the force of air on objects. The particles of air that are all around us push in all directions--that's called air pressure. The card sticks to the rim of the cup because of the adhesive property of water, but it stays in place because of the force of the air pushing into it.

Water is incompressible, which means that you can't squash it to make room for air. When we tap the jar, the force of gravity pulls water molecules down, leaving a region of low pressure in the cup. The force of air moves from the high pressure all around us, into the region of low pressure.

### Objectives

• Explain how air pressure works

### Materials

• Cup or Jar (with ring lid)

• Square or circle of hard thin plastic (a yogurt tub lid, for example) or cue card (thick paper)

• Jug of water

• Square of window screen or mesh (for Part 2)

### Key Questions

• How does the water stay in the jar?
• Part 2: What direction does the air move when you tap the jar? Why?

### What To Do

Part 1:

1. Pour water into the cup
2. Hold a piece of plastic over the mouth of the jar
3. Quickly flip the cup over so the cup is upside down
4. Remove your hand from under the plastic!

Part 2:

1. Cover the mouth of the jar with a piece of screen and use the ring lid to keep it taught and in place
2. Repeat steps 2 and 3 above
3. Remove your hand from under the plastic.
4. Without wiggling or tipping the jar, remove the plastic entirely!
5. Holding the jar over the jug of water, tap the jar to observe what happens.

Survivors

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Egg BB

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

Comet Crisp

Artist: Jeff Kulak

Jeff is a senior graphic designer at Science World. His illustration work has been published in the Walrus, The National Post, Reader’s Digest and Chickadee Magazine. He loves to make music, ride bikes, and spend time in the forest.

T-Rex and Baby

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Buddy the T-Rex

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Geodessy

Artist: Michelle Yong

Michelle is a designer with a focus on creating joyful digital experiences! She enjoys exploring the potential forms that an idea can express itself in and helping then take shape.

Science Buddies

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.

Western Dinosaur

Artist: Ty Dale

From Canada, Ty was born in Vancouver, British Columbia in 1993. From his chaotic workspace he draws in several different illustrative styles with thick outlines, bold colours and quirky-child like drawings. Ty distils the world around him into its basic geometry, prompting us to look at the mundane in a different way.