momentum – The Physics Teaching Podcast

Summary

Dr Dave Farmer joins the podcast to talk about ways to teach Momentum. Thank you for all your input dear listener!

Content

Dr Dave introduces momentum by putting his body on the line (see below). The main themes are increasing collision time to reduce force, momentum as the quantity of motion, colliding students together and doing experiments.

Love it when the TAs help out with demonstrations (Yr 10 momentum). I've still got a headache. pic.twitter.com/tkKsSxAPqF
— Dave Farmer (@ThePhysicsBear) April 4, 2019

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Music

Season 3: 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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We put out the competition not really knowing quite what to expect. Four entries before 8:15am was an exciting start to the day though as I write at 4:30pm it is still four, which has brought me down to Earth somewhat!

Momentum Day

Today was “Momentum” day. After talking with Ben Rogers about cognitive Science (that is in the next episode) I changed the demo away from play (the students making the rockets) and in to a demo so they could concentrate on the key idea of impulse (Ft) being more for the longer rocket, and hence v being higher. I made four rockets myself before the lesson. Showing them the rockets was actually a good way to mention to them that a vernier can be used for internal diameters too. I tried to make all the tubes the same diameter, but it was pretty hard and I think this led to the inevitable inconsistencies in the heights.

There was much uncertainty! The pump was definitely pretty rough at the low pressures I needed to keep the long one below the ceiling, the diameters of the rockets and the release of pressure through the valve all affected each launch. The results were not quantitative at all (my main aim) but it was clear that the longer went higher (on average). I think if I made better rockets on fixed tubes it would be more successful, it is certainly worth pursuing. More massive ones would allow more pressure too.

But as a learning demo it was very good. The idea of the force being constant as the rocket launches and the longer rocket being in contact for a greater time made it easy to imagine impulse and relate it to velocity. At least I thought so. Time will tell.

An Unexpected Misconception

What surprised me was that one person thought that the smallest rocket would go the highest. I’d said that all were made from one sheet of A4 so all were the same mass, but suspect that they were thinking “small is light”.