Science is supposedly rooted in visible truths, but the teaching of it in schools often relies on students' blind faith. Many commonly taught scientific concepts and phenomena are difficult or impossible to see, such as invisible currents of water or air, the motion of light or transfer of heat, and things that happen too quickly or slowly to be seen by the naked eye.
In the past, teachers have found their way around this obstacle in a number of ways, such as diagrams or elaborate models. But modern technology now offers much easier - and much more engaging - ways to make the unseen visible.
Take, for example, the electromagnetic spectrum. Explain to your students that our eyes can see only a small slice of the spectrum: the rest is invisible to us. To prove it, bring out a digital camera and a remote control for a television or DVD player.
Point the remote at your students and press any button. They won't see what is being emitted, as the infrared light cannot be picked up by human eyes. Next, aim the remote at the camera's lens and direct the view screen towards your students. On the screen they will see the "invisible" light emitted by the remote control. Your point is proved.
Digital cameras are also useful for capturing events that happen too slowly to observe. For example, many students hold the misconception that plants grow up from the base of their stems, whereas growth really occurs at the tips of the plant's stem and branches. But because this process occurs so slowly, it is difficult to prove the fact.
To solve this problem, use a technique familiar to anyone with a love of nature documentaries: time-lapse photography. Far from being an expensive or complicated process, it can be incredibly simple. There are plenty of free or inexpensive time-lapse software programmes and apps that turn webcams, digital cameras and other devices into time-lapse cameras - for example, Time-Lapse, which is available at bit.lyTime-LapseApp.
Using a tripod, position your recording device to focus on a quick-growing plant, such as a bean. When your plant is fully grown, play back the video to show your students how it all happened. The same technique can be used to show evaporation of salt water or crystal growth.
Events that happen very quickly, such as two objects of different mass falling simultaneously, can be also recorded. Use your camera's video capture function and import the footage to your computer, so you can replay the event, slow it down and pause on important frames. By using free software such as ImageJ (available at rsbweb.nih.govij), you can measure the size of the objects, their speed and the distance travelled.
And, away from digital technology, there is an alternative to that old friend of science teachers, food colouring. Food colouring has traditionally been used as a dye to show the motion of water currents in a beaker or glass when heated from below, but the dye quickly dissipates and loses its effectiveness. A better option is rheoscopic fluid, available from many science supply stores. This fluid contains tiny crystals, which reflect light and do not dissolve in water, so the water currents can be observed indefinitely.
My students have really enjoyed these ways of demonstrating the invisible in the classroom - and the internet is a plentiful source of more excellent ideas.
Kris Swanson is planetarium resource teacher at Poinciana Elementary Stem Magnet School in Florida, US
TOP 10 CREATIVE SCIENCE RESOURCES
1 Experimental eating
Cook up a scientific storm in the classroom with this booklet of ideas for kitchen-related experiments. The guide contains equipment lists, instructions and a summary of each activity.
2 Sporting science
From testing tin-foil boats to making toilet-roll javelins, these exercises get students to conduct science experiments based on Olympic sports.
3 Slime time
You don't have to have seen the Ghostbusters films to appreciate slime, because every child loves messing around with the gloopy stuff. With this resource, you can teach them some science along the way by asking them to create the slime themselves.
4 Jelly genes
You'll have to watch out for light-fingered, hungry students when you try this activity - it includes the use of sweets. Introduce DNA by asking students to create their own double helix using jelly babies and liquorice.
5 Over the limit
This set of activities gets students to create their own breathalyser tests.
6 Insulating instructions
Mushrooms, a baked Alaska dessert and hay-box cookers may not sound as if they belong in a lesson on insulation and sustainability - but this resource pack proves otherwise.
7 Under the lens
In this visual lesson on how sight works, teach the biology of the eye using the technology behind photography.
8 Special lessons
Explore the science behind special effects with this presentation on five different techniques. Your students will enjoy this blockbuster lesson that features fire-writing and flaming bubbles.
9 Tea and toast
Children investigate ways to keep Mrs Hardie's cup of tea warm and insulated in this interactive whiteboard video, which makes for a compelling science lesson.
10 Fuel for thought
Get students interested in the mysteries of propulsion with this water bottle rocket challenge. It promises to fire up even the most reluctant of scientific imaginations.