The Physics Teaching Podcast

Tag: jelly chair

  • Newton’s Laws for Non-Specialists

    Newton’s Laws for Non-Specialists

    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

    Join in!

    Please share ideas or successes – or indeed questions by messaging us on BlueSky: https://bsky.app/profile/physicstp.bsky.social .  You can also message us via our website contact form on every page of the web site at  the.physicsteachingpodcast.com, or email using the address given in the podcast (if we remember). We are moving away from X but can be found there as @physicstp.

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  • Refutation Text for the Jelly Chair

    Refutation Text for the Jelly Chair

    I said in Episode 6 I would share what I came up with for the Jelly Chair lesson and refutation texts. I did put some thought in to this but think that there is room for improvement. I ended up writing a few sentences for the kids to do:

    • The ancient Greeks thought that arrows were pushed through the air by the god Apollo. We know this is wrong because…
    • Many people think that objects will slow down and come to rest if no resultant force acts upon them but really…
    • A typical GCSE level understanding of balanced forces allows a person to sit on a chair made of jelly. This is false because…
    • Galileo showed that two balls of different weights accelerate at the same rate when dropped.. Before this people thought heavier objects fell faster but this is wrong because…
    • Some people think the International Space Station has no forces acting upon it because it is in Space, the evidence that they are wrong is…
    • When a helicopter is hovering it is very common for people to think that the weight of the helicopter has an equal and opposite force that is the down-force from the rotors. This is wrong because…

    I was particularly happy with the last one (though I have no idea if that is an actual misconception or not), and even happier when one of the students said something like:

    The down-force is equal to the weight!

    They had truly understood the situation, and was able to explain to their partner that the weight and down-force must be equal in magnitude and in the same direction as weight if the helicopter is hovering (not equal and opposite).

    As I roamed the class and spoke to the students I was pretty confident the refutation sentences were having impact. The challenge is to use them again and again and embed them in my practice.

    The podcast strikes again. Thank you Ben Rogers!

  • 6. What happens when your jelly won’t hold your weight? Is it time to lose some mass?

    6. What happens when your jelly won’t hold your weight? Is it time to lose some mass?
    Jelly chair aftermath

    Thomas and Robin got together in the same room for a chat this week. Don’t worry, as a good physicist and a good engineer they avoided eye contact*. The big news last week was the redefinition of the kilogram which was originally based on the mass of Napoleon’s leg**, but latterly on a  lump of metal held in what looked suspiciously like a cake container. So we discussed misconceptions about mass and weight and about one of Thomas’ favourite experiments: the jelly chair.

    *Well, that’s an unhelpful stereotype!  In fact we were highly empathetic and talked about our feelings extensively.

    **completely made up

    Competition! 

    Now we have listeners, AND an Instagram page (@physics_teaching_podcast) we thought we would encourage you to share the podcast by having our first competition. Win a beautiful podcast T-shirt (in the colour of your choice) by interacting! To win, tell us why you like listening. There are many ways to do this:

    Thomas and Robin will pick a winner in a couple of weeks.

    It remains an enthralling and inspiring adventure making this podcast for you.  You’ve already taken it in directions we weren’t expecting; it really is your podcast, so please get in touch: teachers of physics are our very favourite breed of hero!

    Join in!

    Please share ideas or successes – or indeed questions by messaging us on BlueSky: https://bsky.app/profile/physicstp.bsky.social .  You can also message us via our website contact form on every page of the web site at  the.physicsteachingpodcast.com, or email using the address given in the podcast (if we remember). We are moving away from X but can be found there as @physicstp.

    Music

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