Science of Airflow, Motion, and Lift

Every week, Madison (my 10-year old daughter) and I teach a 1.5-hour afterschool science club for K-2^nd graders.  Each week she helps plan the lesson and then we write the blog about what we did. 

We have provided links to the books we used to sneak in some literacy.  We learned most of the science experiments and activities from Steve Spangler (awesome speaker and science guy extraordinaire).  We have included links to his science supplies, experiments, and videos.  We also include links to our YouTube videos. These links take you away from the blog and to external websites.

Lesson 6

Science of Airflow, Motion and Lift

Science Standards Addressed:

• Make observations, predict results and develop questions (Puff Cars).

• Know that air takes up space and exerts a force (Potato Launcher, Windbags).

• Observe that the motion of an object can be affected by pushing or pulling it (Ping Pong Balls and Wind Bags).

• Describe ways to make things move and what causes them to stop (Puff Cars, Ping Pong Balls, Potato Launcher).

• Describe how force can change an object’s motion (Puff Cars, Potato Launcher, Ping Pong Balls).

To create curiosity and a little healthy confusion, we put out a snack of raw potatoes and juice. The potatoes were really for our grand finale’ activity.

Then we brought out the real snack.

To sneak in a little literacy (and a science hint) Madison read, 

 - about Mr. Small, a high-flying pilot. Pilot Small prepares for his flight, and then enjoys the bird’s-eye view from above. It has lots of details about how planes fly. 

- about a sassy Siamese cat named Henry that wanted to fly with his family in their hot-air balloon, but the man always said that he wasn't flying with a cat.

 Then the balloon accidentally took off with just Henry in the balloon! Henry has an exciting adventure in the air before floating back down.

Materials available: 3 straws, 50 cm of making tape (kids measure), 1 piece of card stock paper, 2 paper clips, 4 lifesaver candies, and a ruler.

Once our cars were completed, we predicted how far they would go in 1 blow.  Then we tested it out!  We tested each car and measured the distance the cars went.

Then we developed questions – what if…?  We hypothesized on how we could improve them and kept adjusting and improving the cars until time ran out!

Since this activity required some teamwork, we debriefed our skills. 
We asked what worked, what didn’t, what they would do differently if they had a chance to do it again.  Did everyone participate?  Was everyone’s voice heard?

We heard “No Way!” “Whoa!” “How can it do that?”

The pressure in the tube becomes even lower than that of the air surrounding the ball, and the ball is pushed up into the tube – and accelerates out of the top – swoosh!

We also did a lung-powered version of this experiment by blowing air into bendy straws to create the column of air. 

Airplanes can fly because of Bernoulli’s principle. As a wing moves through the air, air divides and flows around the wing.

So the relatively greater air pressure beneath the wings supplies the upward force, or lift, that enables airplanes to fly.  There is also the whole “angle of attack” that enables flight, but this is already getting way too advanced for second graders.

The kids predicted that it would take about 40 breaths to inflate the whole bag.

What’s the science of this?  Remember Bernoulli’s Principle. When you blow a stream of fast moving air into the bag, you create low pressure.  So, the higher pressure air in the atmosphere shoves its way right into the bag along with the air from your lungs.

They put a pretty large fan outside of a much larger opening and use the fan to help
push some atmosphere into the balloon.

We held the tube in one hand and the plunger in the other and pushed upwards on the bottom end of the plunger – pushing the bottom plug towards the top plug until POW – the top plug explodes out!

Then we just loaded a new plug and repeated.  

When we decrease the volume of the air trapped in between the two pieces of potato,
we increase the pressure – which the pressure which eventually forces the
top potato plug to shoot out like a rocket!

Plus we snuck in some speaking and listening standards like asking questions, expressing ideas, following multi-step directions, and participating in discussions.

See our YouTube Video: Bernoulli's Principle and Lift

10 minutes

As the children arrived we played the songs Up Up & Away, by the Fifth Dimension, and Leavin on a Jet Plane, by Peter, Paul, and Mary.

The Little Airplane, by Lois Lenski 

and Hot Air Henry, by Mary Calhoun.

We picked this book because of the true-to-life artwork that is well-researched, and accurately depicts real life ballooning.  We live in the home of a HUGE annual balloon fiesta, so most of our kids have seen this in person.

30 Minutes

Puff Cars

To engage their emotions and get them into a creative state, we created an imaginary situation.  We told the kids that because there is a global warming, an energy crisis, and a recession, the great automotive companies are in trouble.  They have asked for a government bailout and for the help of scientists everywhere.  They need our help!  Our challenge is to build a model for an air-powered car, using only the materials available to us and within the limited timeframe. 

15 Minutes
Ping Pong Balls and Bernoulli

We set a hair dryer to cool, switched it on, and pointed it at the ceiling.  Then we carefully put the ping-pong ball into the stream of air.  We dropped the ball a few times, but eventually if we held the hair dryer really steady, the ping-pong ball would float in the stream of air. Gravity was pulling the ball downwards, but air from the hair dryer was pushing it upwards. All the forces acting on the ball were balanced so the ball hovered in mid-air. We could even sway the hairdryer thisway and thatway and the ball would stay in the stream of air. 

The floating ping-pong ball is a wonderful example of Bernoulli's Principle - the faster air flows over the surface of something, the less the air pushes on that surface = less pressure.  So, we made the ball follow the stream of air as we swayed the hair dryer because the fast moving column of air around the sides of the ball exert less pressure than the surrounding stationary air. It is held in the column of air by the higher pressure air pushing on it from all around outside the stream. If the ball tries to leave the stream of air, the still, higher pressure air pushes it back in - so the ball will float in the flow no matter how you move.

When you place the empty toilet paper tube into the air stream, the air is funneled into a smaller area, making air move even faster. 

We had to help the kids to place the balls on the end of their straws as they blew, but they were able to keep their ping-pong balls floating for a few seconds.

The top surface of the wing is curved, so air travelling over it has farther to travel to reach the trailing edge of the wing. To travel across the wing in the same amount of time, air moving across the top of the wing has to go faster. Because it's moving faster, the air on top of the wing exerts less pressure on the wing than the air below the wing. In other words, air below the wing pushes up more than air above the wing pushes down. 

To demonstrate this, we gave each child two strips of paper and asked them to hold one in each hand.  We asked them to predict what will happen if they were to blow between the two flat sheets. Most of them said the papers will separate and go out away from the space they blow into, because usually things move away when you blow them right. Then we let them to try it. The result was not what they predicted - the two sheets of paper came together. This is because the blowing creates a tunnel of fast moving air between the sheets of paper and lowers the air pressure between them. The higher pressure on the outsides pushes the sheets in to touch each other.  

20 Minutes
Windbags

We purchased some "Windbags" - long plastic bags in the shape of a tube. Full Experiment.  We tied a knot in one end of the bag, used my hand to make the open end into a small hole, and asked a volunteer to blow four large breaths into the bag.  We compressed the air he blew in down to the knot to see the volume of air blown in and how many more breaths it would take to blow up the whole bag.

Then I challenged them to race me.  The volunteer tried to continue to inflate the bag by blowing into the small opening, but I held the open end of the bag approximately 10 inches away from my mouth, and blew one BIG breath - as hard as I could you into the bag. The entire bag inflated and the race was over in a flash.  And the crowd went wild!

This is the same way they inflated the hot-air balloon in Hot Air Henry – the book we read earlier.  

15 Minutes

Potato Launcher

Safety Note: In this activity we will basically be shooting hunks of potato at pretty high speeds, so of course we took safety precautions.  Note the safety goggles and note that all children are standing behind the shooter.  When we asked the kids why they thought the safety glasses were necessary, they said "Duh, we're going to be shooting stuff!" 

OK – now that the guys in suits are happy…

We purchased these totally awesome potato launchers from you know who. Full Experiment. It is basically a hollow tube and a plunger with a stopper that fits into the tube.  We cut some potatoes in half lengthwise and laid them on the sidewalk.  We pushed the tube into a potato to pull out a potato plug.  Then we used the plunger to move the plug to the other end of the tube.  Then we added another plug in the same way.  Now we had two plugs – one on each end of the tube. Now for the fun part!  

We actually shot our potato pieces right into the school compost pit.  NO CLEAN UP!  We are safe, responsible, AND smart!


The youngest kids needed help loading the potato plugs and with the strength to push the plunger, but it was still SO awesome!

We told them, "Boyle's Law states that pressure and volume are inversely proportional." 


NO – we didn’t use those words.  We said that as we reduce the amount of space that a gas is in, we increase the pressure. 

To create an imaginary situation, we told them to imagine that they were in a school bus.  Then imagine that we stuffed about 100 more kids into that bus.  Then 100 more kids.  Pretty soon there would be a lot of pushing and shoving and a lot of pressure on the bus.  Now we said to imagine the bus began to shrink – even less space and even more pressure.  That is kind-of what happens in the potato launcher.

Awesome grand finale’!