Windbag challenge, spray straws and definitions

Miss Laverty 2012***experiments, lesson and worksheet adapted from the Edmonton Public curriculum book ***

March 8th, 2012

1) Hand out the work books2) Grab today’s handout3) Sit down and show me you are ready to try

the “windbag challenge”

Windbag Challenge

• Challenge: to inflate this bag as much as you can with just one breathe

• Materials: long plastic bag (or an actual windbag if you have one) and a person with strong lungs

Windbag Challenge

• Describe the method that got the bag to inflate the most in just one breath?– The bag inflated more when we made a larger

opening and held it near our mouths without making a seal

Windbag Challenge • Draw a diagram to represent how we inflate the bag so easily. Be sure to

show the direction of the air flow and “high pressure” and “low pressure” (HP and LP) in your diagram. Use colours to represent the low and high pressures

Windbag Challenge

• How is this example of Bernoulli’s principle?– BP states that fast moving air exerts less pressure

on the surfaces that it passes over – Since the air is moving quickly, we know that it is

creating a low pressure area as it enters the bag

Spray Straws

• Materials: drinking straws, plastic cups, and water

• Procedure: 1. Fill a glass about three quarters full of water 2. Secure one straw inside the plastic cup with one

end in the water 3. Take a second straw and hold it perpendicular to

the first straw 4. Blow through the horizontal straw

Spray Straws

Spray Straws

• How does the fast moving air lift the water?– the fast moving air creates a low pressure area at the top

of the vertical straw– The normal air pressure of the room is now considered

high– We know that air moves from high to low pressure– So since there is a low pressure area at the top of the

straws, the normal air pressure of the room is able to lift the water up the vertical straw

– The water sprays when it goes up the straw because it gets into the fast moving air stream

Spray Straws

• Real life example:– Paint sprayer/airbrush

DEFINE

• Bernoulli’s Principle: – When air moves quickly it exerts less pressure

over the surfaces that it passes over • Examples: funnel and ball, pop cans, paper

tents, toilet paper, strip of paper, spray straws• http://www.youtube.com/watch?v=bv3m57u

6ViE

DEFINE

• Lift:– upward force

which acts against the force of gravity

DEFINE

• Gravity:– A force that attracts all objects with mass to the

Earth

• Gravity Bill Nye: http://www.youtube.com/watch?v=hZi8TXtRRYg