Show and fly a paper airplane. We will make one.
It flies because of Newton’s Laws.
List Newton's Laws, while adding the forces to a drawing of the plane next to the list (see photo):
Newton’s 1st Law Objects stay stopped or in constant motion until a force acts on them (Thrust, drag, gravity)
(A force might make an object start, or stop, or change direction)
Newton’s 2nd Law F=ma (More or less thrust)
A bigger force will make the same mass accelerate more
To move a bigger mass, you will need a larger force move it the same
With the same force, a smaller mass will accelerate more than a larger mass
Newton’s 3rd Law For every action there is an equal and opposite reaction (Lift)
(When an object pushes on another it gets pushed back with equal force)
Expand on the Forces, as needed:
Thrust:
Makes the plane move forwards. Your arm muscles give it thrust; a harder throw gives it more thrust.
Real airplane: the thrust is from a propellor or jet engine, and is continually acting as the plane flies.
Drag / air resistance:
The force that slows a plane down as it pushes against the air as it moves. It is a kind of friction. It acts in the opposite direction from thrust.
Thrust must be greater than drag for a plane to go forwards.
Streamlined objects have less drag (there are more streamlined paper airplane designs). Airliners retract landing gear in flight so it is not ripped off by air resistance.
Gravity:
The force pulling a plane downwards.
(It acts on the mass of the plane, giving it weight.)
Lift:
Pushes the airplane up, acting in the opposite direction of gravity.
Lift is produced by the wings and the air flowing off them. The tilt of the airplane (the 'angle of attack' and the angle of the wing shape (where relevent) makes air flow off the wing downwards (the 'action' of Newton's 3rd Law). This downwards force pushes back against the wing ('reaction' of Newton's 3rd), and pushes upwards on the wing.
Either the wing or the air must be moving - they just need to move relative to each other, for lift to be generated.
(The Bernoulli effect has previously been used to explain lift, but is now known to be insignificant, or even incorrect - it doesn't explain how some planes can fly upside down.)
As an aside, drag and lift can be felt effectively with a hand out of a moving car window:
Holding your palm flat against the wind you can feel the air pushing against it: drag, or air resistance. If you make a fist, your hand is smaller and there should be less drag on it.
If you hold your horizontally flat hand straight out of the window, then slowly rotate your wrist it so the front edge of your hand tips up a bit, the air is directed downwards and pushes your hand up. The effect is quite dramatic as it kicks in, and nicely demonstrates action and reaction.
Students make their paper airplanes, with assistance if needed. Make sure students make the creases accurate and tight (run a nail over folds).
If they want to make their own, keep it simple - no flaps yet.
Fly it. Get a consistent thrust. Ask students to think about the forces on their planes as they fly them.
Note you get more Lift by changing the angle of attack (point it upwards to start).
Then step through these changes as a class:
1. BEND UP the outside back of the wings (see photo), by 45 degrees (not a right angle). Air flowing off those bends upwards (action) pushes the back of the plane down (reaction), lifting the nose of the plane. This should keep the plane aloft for longer.
If the nose of students' planes rises upwards too steeply, the plane will suddenly drop: the plane is 'stalling'. Make the bends a smaller angle.
2. BEND DOWN the back of the wings to make more air flow downwards off the back of the plane (action), which pushes the back of the plane up (reaction), which tips the nose downwards. Students' paper airplane might nose-dive with this modification!
3. SPIN the plane by bending the back of one wing down, and the other up.
Newton's 3rd Law of Action and Reaction explains how all these flap changes effects the flight of the paper airplane.
In real planes, some wings also have 'winglets', which are upwards folds on the wing sides, to reduce a vortex of air that pushes the wing down.
4. Students may want to try cutting and folding flaps in their planes, to see how they affect the flight.
Encourage students to share designs, and allow more time for testing.
They can optionally measure and record how far their plane goes. Optionally generate a class graph of the distances achieved, and discuss factors that might increase flying distance.
Airplanes, Cars and Birds use Newton’s Laws (photos/video):
Real airplanes: use flaps to keep the plane level during flight and after landing (see photos).
F1 cars: show DRS system. For going around corners fast, they have no DRS, as the air flowing off the rear wing pushes the back of the car down, keeping it from sliding off the track (Newton's Third Law). On long straight stretches they use DRS ('drag reduction system’): reduces the downforce so go faster.
Birds: glide for the same reason that paper airplanes fly, using lift.
They also push air to take off and manoeuvre. Show slo mo birds (Wings lesson)
Air seems like nothing to us as we are heavy. When a light bird pushes against air particles, they are small enough that the push makes them move.
Just as adjusting your plane changes the flight, birds move their feathers (with muscles) to change their flight path.
And depending on which way they push, they can make amazing maneuvers in the air.
Note: the shape of birds’ wings are different on the downstroke and the upstroke.
Optional alternative focus:
Airplanes modelling bird wing shapes
Build differently-shaped airplanes, to model how some birds have wide wings for gliding, and others have swept back wings for fast flying. See this link for designs: https://www.audubon.org/news/these-paper-airplanes-fly-birds See the paper raptor designs from this link: http://idahoptv.org/sciencetrek/topics/birds_of_prey/activity3.cfm
Some birds of prey have swept back wings, so that they can dive at high speeds and catch other birds (e.g. peregrine falcon).
Some birds have long, wide wings to help them glide and look for prey e.g. hawks, eagles. They can open their wing feathers at the ends to keep the airflow around the wingtips smooth and to prevent stalling at low speeds.
Some birds have short broad wings and long tails to allow tight manoeuvring and quick takeoffs e.g. woodland hawks. However, they need to flap a lot.
