THERE is a deep satisfaction to be had from making and throwing a paper plane. From the number I have had fly across my classrooms, I have been able to ascertain that most children over the age of 11 know how to make one, albeit of varying quality.
I wouldn鈥檛 be doing my job properly if I didn鈥檛 encourage further experiments. They might investigate the factors that contribute to a good flight, and find out for themselves the importance of precise folding and the exact position of the centre of mass. Apparently, real scientists also do this sort of thing and get their work .
Advertisement
I also like to show my students how to make paper helicopters, because far fewer people seem to know about these and they are just as delightful to play with.
Start, as shown in diagram 1, above, by cutting an A4 piece of paper into a rectangular strip about 6 centimetres wide and 20 centimetres long. Make three cuts in the paper, as shown by the red lines in diagram 2, above left.
Fold the paper along the dotted lines shown in diagram 3, above. If you have one, attach a paper clip to hold the bottom flap closed. Bend the 鈥渂lades鈥� in opposite directions, as shown in the final image, then hold the helicopter up by its stem and drop it.
The thing that surprises most people who haven鈥檛 seen this before, is the fact that the helicopter starts spinning by itself. You can explain to the child, as you do the experiment, that when you drop the helicopter, air is pushed into the folds where the blades meet the stem. The asymmetric structure of the helicopter, with each blade attached to half the stem on opposite sides, means that air pushes each side of the stem in opposing directions but along parallel lines, producing what is known as a couple.
This makes the stem rotate, a bit like when you spin a coin on its edge by pushing on both sides at the same time.
The blades are pushed upwards by the air as the helicopter falls, so that they aren鈥檛 horizontal. This means that, as they spin, they experience a lift force 鈥� like when you hold your hand out of a moving car window at an angle. This reduces the effect of gravity on the helicopter and causes it to fall more slowly than it would if it weren鈥檛 spinning.
Show the child you are with that their helicopter should fall in pretty much the same way every time they drop it. This reliability makes it ideal for doing some experiments. What do you think will happen to how fast it spins and falls if you attach one or more paper clips to the bottom? Why? How could you make it spin in the opposite direction? How could you make it fall faster or slower?
What you need
A sheet of A4 paper
Scissors
A ruler (optional)
One or more paper clips (optional)
Alom Shaha is a physics teacher at a comprehensive school, and author of books including Mr Shaha鈥檚 Marvellous Machines. Follow聽him @alomshaha
These articles are posted each week at
