Science - 'Sir, why don't you like dogs?'

30th March 2012 at 01:00

What the lesson is about

Teaching terminal velocity needs a staged approach where the teacher can explain each development in the motion - a smartboard can help, and a bit of humour, writes Simon Porter.

A dog (accidentally) falling from an aeroplane at first has only the force of gravity pulling it down, so it will accelerate (slide 1). As the dog goes faster (slide 2), the force of air resistance increases but, because it is still less than the force of gravity, the forces are unbalanced so the dog continues to accelerate.

Eventually (slide 3), the force of air resistance becomes equal to the force of gravity, so the forces become balanced and the dog falls at a constant speed (called terminal velocity).

The staged approach means the teacher can go back and forth rapidly between the slides when pupils need to have a point repeated or reinforced, and slides can be printed out for them to stick in their books.

Taking it further

The same approach can be used to explain orbital motion and centripetal acceleration. A dog can be kicked horizontally off a table only a certain distance (slide 1).

A small cannon is required to fire the dog horizontally further, but the dog is still pulled down by gravity (slide 2). An even larger canon (slide 3) will fire the dog even further than expected, as the curvature of the Earth now has to be taken into account, although gravity continues to pull - and thus accelerates - the dog towards the Earth, and so on.

Where to find it

Simon's "dogs in orbit!" and "dogs falling from aeroplanes" can be downloaded free from TES Resources.

Subscribe to get access to the content on this page.

If you are already a Tes/ Tes Scotland subscriber please log in with your username or email address to get full access to our back issues, CPD library and membership plus page.

Not a subscriber? Find out more about our subscription offers.
Subscribe now
Existing subscriber?
Enter subscription number


The guide by your side – ensuring you are always up to date with the latest in education.

Get Tes magazine online and delivered to your door. Stay up to date with the latest research, teacher innovation and insight, plus classroom tips and techniques with a Tes magazine subscription.
With a Tes magazine subscription you get exclusive access to our CPD library. Including our New Teachers’ special for NQTS, Ed Tech, How to Get a Job, Trip Planner, Ed Biz Special and all Tes back issues.

Subscribe now