Fight Science: Momentum

Holding up a large cushion in front of me to absorb some of the impact and standing in front of the sofa so that I had a soft landing, I asked the kids to take it in turns to run at me full tilt to see what happens.

Talon, the smallest, didn’t hold anything back and he bounced off of me as well as knocking me down. Aidan put just enough umph into the impact to knock me over without losing control of his own momentum. I progressed the lesson once they were getting the hang of it and I moved out of the way at the last minute, watching them pummel themselves into the sofa. After this event they held back how fast they were running so that they could stop in time.

I wanted them to feel their momentum impacting purposefully and the feeling of helplessness once your momentum is taking you in a direction not of your choosing, the sofa.

Moving to the whiteboard I posed some question to them in the form of a half finished diagram: what would happen if a fly zoomed into a market stall selling teapots. I loved the answer “it would shoot down the spout of a teapot". I drew the trajectory and showed that the fly would just bounce off of the stall.

Replacing the fly drawing with a charging bull, the same question was asked. What is the difference between the fly and the bull? One of them said that the bull was heavy and that’s what I wanted to hear. Mass is part of the momentum equation so I wrote that on the board. “no not ‘maths’, ‘mass’" I had to say a couple of times.

Now what would happen if the bull walked at the stall instead of charging at it? It’s not going to destroy it, but push it around. Velocity is also part of the momentum equation, but speed is only half of the velocity equation, direction is the other and we can draw this as an arrow pointing towards the stall.

Draw an arrow for the fly and one for the bull. We can change the shape of the arrow to signify the amount of momentum.

Direction is something that can be harnessed when fighting somebody, allowing you to use their momentum against them. If you are running along and I suddenly change your direction to point at the floor what will happen? Ouch indeed. Or the ceiling? Yep, a funny drawing opportunity on the whiteboard.

Kneeling up and facing parallel to the sofa which was a few feet away, I got them to charge at me again. This time I changed their direction to be an upward angle and they flew through the air to land on the sofa. Repeat ten times. Next, I tripped them over, keeping hold of them to remove the impact with the floor, then I let them trip me onto the sofa. Spinning each other around and trying to take out the other person's legs was a fun game we invented on the spot, but I had to be careful not to be the one tripped so that we didn’t have a giant crushing nearby children or furniture.

Back to the whiteboard. Draw the momentum of a tennis ball being hit, "yes the size of the arrow tapers near the end, very good". How about a ball rolling down a hill, “it gets faster? A bottom heavy arrow then". “How about something being dropped off of a building?". The mental model of momentum has been grasped. Time for sparring.

Kneeling in front of one child at a time, we bowed and then wrestled one or the other to the ground, focussing on how to use my momentum against me. They are spry and could get out of my way if I overextended myself, or they could pull down on my arms when I reach for them to change my direction to point me into the floor. I made sure to win a few times to use their mistakes against them.

Standing wrestling is round two, with much spinning around for me, and much tripping up for the kids. Over an hour had passed since we started the lesson and it was time to draw it to a close.

Can an understanding of momentum help in a fight? “Yes" the kids respond. The last thing we do is write up both equations for velocity and momentum on the whiteboard and I leave the words blank for them to fill in to see if they remembered.



If you would like the lesson plan that I wrote up for this session you can view it and download it here: Fight Science: Momentum. My kids love play fighting and I used this as a platform to teach them about science, inspired by the book Fight like a Physicist.


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joe@joejames.io. You wont find me on social networks (because I'm not there).