Newtons Laws for Non-Specialists

The Physics Teaching Podcast

So fundamental… such a minefield. Newton’s laws are central to school physics and so can be daunting for those heroes who teach physics but would not describe physics as their specialism. Even as specialist physics teachers, Thomas and Robin have struggled with “reaction”, free body diagrams and force arrows so it was great to welcome physics coach, teacher educator and veteran of “S1E1” Jessica Rowson joins us to put things right.

Jessica is a teacher educator and senior lecturer at St Mary’s Twickenham, as well as Teaching and Learning Coach for the Ogden Trust. If you need any help with science / physics teaching or CPD, she can be contacted via the links below.

Jessica, Thomas and Robin had a suggested teaching order as follows. You can find links to help you on the specifics below, as well as some useful forces resources

• Start with the idea of a force as a ‘push or pull’
• Introduce and explore force arrows that reflect both magnitude of the force (length of arrow) and the direction of the force (where arrow is pointing).
• move on to sketching common objects and forces on them (Free Body Diagrams). Be careful to get students to abstract objects to ‘blobs’ before you lose a lot of time with artistic renditions of bikes or Ferraris).
• Now on the laws themselves – start with Newton’s 3rd.
• MISCONCEPTION ALERT: there is often confusion between normal supporting force and reaction force as described in Newton’s 3rd.
• It’s vital to be clear on the wording of Newton’s 3rd: if object A exerts a force on object B, then object B exerts an equal and opposite (reaction) force on object A of the same type.
• Spend some time working on the misconceptions around newton’s 3rd with plenty of examples.
• Move on to Newton’s 1st law and the idea that a resultant force results in a change in motion.
• MISCONCEPTION ALERT: Students will believe that a moving object has a force acting on it. This dies hard and so lots of examples needed here! Look at the BEST resources in the links section for some help!
• Address the idea that objects on earth slow down and stop BECAUSE they always have resistive forces (friction or air resistance) acting on them.
• Lastly, address Newton’s 2nd law where we can work out the change in motion that a resultant force causes.
• We recommend introducing the iconic formula in the form a=F/m. Why? The acceleration is the change in motion, and can be quantified as the ratio of force to mass.

Jess finishes with a description of a great experiment that will help students to think through the ideas of forces: any experiment involving a radio controlled car must be a winner.

Thomas’ PowerPoint on Newtons-Third-LawDownload

Links

• Jessica Rowson at the Ogden Trust and St Mary’s Twickenham
• BEST on Forces and Motion
• IOP Spark Forces CPD
• How to draw force arrows…
• force arrows and free body diagrams

Join in!

Please share ideas or successes – or indeed questions – on our Facebook Page: https://fb.me/physicstp . You can also message us via our website contact form at the.physicsteachingpodcast.com, Twitter @physicstp, email using the address given in the podcast (if we remember), you could even email us an autio file if you are feeling really keen.

Music

• Season 5: Crescents by Ketsa.
• Seasons 3 and 4: Disco Sheik by Podington Bear.
• Seasons 1 and 2: One legged equilibrist polka by Circus Homunculus.
• Occasionally we also use Cantina Rag by Jackson F. Smith.

The music is used under the Attribution-NonCommercial 3.0 International License

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