Video transcript of Episode 5: Wobbly Stick
On-screen text reads: "Do Try This at Home from the Institute of Physics. Episode 5: Wobbly Stick."
Camera shows a split screen. On either side, two members of Jenny’s family are seeing how long they can balance a long stick-like object on the tips of their fingers. There is a timer in the centre of the screen, and we can see it count the number of seconds accompanied by a beep. One competitor manages to balance his stick for 4 seconds, and the other for 6 seconds.
The camera cuts to a medium shot of Dr Jenny Search who is about to present the experiment.
Jenny: "Hi and welcome to Do Try This at Home brought to you by the Institute of Physics. We’re making these films to help parents and carers across the UK and Ireland get their kids curious and excited about science, even when you can’t leave the house.
"My name’s Jenny, welcome to my home. The demo I’m going to show you today is called the Wobbly Stick challenge.
"You don’t need a lot of stuff for this demo. You need something long, ideally over about 50 centimetres. We had a look around our house and this is the type of things that we found."
Jenny then picks up some household items that could work for the experiment, showing each one to the camera.
Jenny: "A garden cane. A strut of wood from some piece of furniture that we took apart some time ago.
“If you can’t find anything suitable you could even make your own long stick by rolling two sheets of paper together twice and then sticking it together with some Sellotape."
"You’ll also need something to add mass to the end of your stick, so this is some Play-Doh that we made at home. You could use some Plasticine or even a lump of Blu-Tack.
So, to set up your challenge you just need to put the Play-Doh on one end of the stick and you’re ready to go."
Jenny picks up a lump of Play-Doh about the size of her fist and pushes the end of the stick through the centre of it, so that it sits close to one end of the stick.
Jenny: "Now you can challenge your family to the world premiere of the IOP Balance Off!"
We hear some game show music, and see some on-screen text which reads: “Balance-off.”
Camera cuts to the garden where the first of the two contestants is twisting and rotating his garden cane, looking very confident. Jenny is no longer on camera. Instead, we hear her as the narrator.
Jenny (voice-over): "Contestant number one: AJ, with a superior sense of balance and style."
Camera switches to the second contestant who is twirling a wooden strut and looking like he means to win.
Jenny (voice-over): "Contestant number two: Cav de Best has always dreamt of winning a back garden balance-off."
Jenny (voice-over): "Round one!"
On-screen text reads: "Round One". The camera then switches to a split screen, with AJ on one side, and Cav de Best on the other.
Jenny (voice-over): "Each contestant must keep the Plasticine at the bottom and balance the stick on the tips of their fingers. The longest time is the winner. Three, two one... balance!"
The timer appears in the centre of the screen and counts to 6. We then hear a buzzer sound because Cav de Best can no longer balance his stick, and he almost drops it.
Jenny (voice-over): Round two!
On-screen text reads: "Round two."
Jenny (voice-over): "Each contestant must balance again but this time with the Plasticine at the top of the stick. Three, two, one... balance!"
Both contestants start again but this time the Play-Doh is towards the top of the stick. As be-fore, they move around to rebalance the stick every time it starts to tip. The stick AJ is balancing falls over at 7 seconds and we hear the buzzer. Cav de Best managed to balance his stick for 12 seconds and we hear some music to celebrate together with some clapping from the audience. Cav de Best is delighted with his victory and walks towards the camera with a smile on his face.
Jenny: (voice-over): "An excellent effort from both contestants."
Camera cuts back to medium shot of Jenny.
Jenny: "Our balance off shows that it’s easier to balance the stick the further the blob of clay is from your hand. But what’s going on here and how can you explain it to your family?"
Jenny picks up a drumstick and places it upright in the palm of her hand. The Play-Doh is to-wards the top of the stick.
Jenny: "For the stick to stay balanced you need to keep your hand directly under the mass, the piece of Play-Doh. Gravity is pulling down on this piece of Play-Doh and your hand is pushing directly upwards to counteract that force. But this can’t last forever. As soon as the stick starts to tip over gravity is still acting on the Play-Doh causing the stick to tip over more and more, faster, and faster. To get it balanced again you need to move your hand directly under the piece of Play-Doh."
As she speaks, Jenny taps the side of the Play-Doh with her first finger to show where gravity is pulling on the stick to tip it over. She pushes her hand upwards to show the hand counteracting gravity. She shows the stick starting to tip over and counteracts this by moving her hand underneath the Play-Doh again.
Jenny: "You’ll have discovered in the balance-off the stick moves more slowly when the mass is at the top of the stick, but why is this?
"So, you can try waving the stick and you’ll find it’s much easier to wave when the mass is near your hand. If the rod tips over when the mass is at the bottom it only has a short way to move but when the mass is at the top it has further to move which takes longer giving you more time to move your hand underneath the Play-Doh again."
Jenny holds the drumstick horizontally but at the opposite end to the Play-Doh and waves it up and down. She then holds it at the other end and repeats the same action. She then rests the stick upright in her hand and by tipping the stick over shows the difference in distance travelled when the Play-Doh is closer to hand versus when it is at the other end.
Jenny: "Think of pushing someone on a swing. If something is difficult to start moving, we say it has a lot of inertia. It’s much harder to start a heavy person swinging than a light person. A heavy person has more inertia."
At this point, the camera cuts to Cav de Best who is trying hard to push a giant toy dog on a swing. He looks like he’s struggling to start the swing.
The camera cuts to an empty swing. Cav de Best is standing behind it and places a small caterpillar toy on the same empty swing. We hear the ring of a bell as Cav manages to push the swing with just his first finger. He smiles because it’s so easy.
The camera then cuts to a roundabout made of Lego.
Jenny (voice-over): "Still in the playground, it’s much harder to push the heavy person round the roundabout if they stand near the edge. There’s more inertia than if they sit at the middle."
The camera shows one Lego person sitting at the edge of the roundabout whilst four Lego people push him around. The roundabout moves slowly. The camera then switches to the Lego person sitting in the middle of the roundabout. This time only one Lego person is pushing him around, and the roundabout moves more quickly. We hear the Lego person on the roundabout cry delightedly.
Jenny (voice-over): "In the same way, moving the lump of modelling clay so that it’s further away from your hand gives it more inertia. The stick tips more slowly and it’s easier to keep balanced."
The camera switches to Cav de Best balancing the stick in his hand. The recording is in slow motion, so we see him adjust his hand position to keep the drumstick balanced.
The camera then switches back to Jenny.
Jenny: "Don’t worry if you’re not too sure about the science. The most important thing is to try it out and have fun together, test different things out and then if you need to, look it up together afterwards. Thanks for watching. Have fun - goodbye!"
We hear the game show music again, our two competitors each side of a split screen, twirling their sticks like ninjas. The on-screen text reads: "Game Over."
The image fades to be replaced by some new on-screen text, which reads: "Do Try This at Home from the Institute of Physics. For instructions and more Do Try This at Home films visit iop.org/athome. These experiments have not been specifically safety tested for home use, but we believe them to be safe if the instructions are followed. Adult supervision is recommended as appropriate. All experiments are carried out at your own risk."