Video transcript of Episode 4: Reversing Arrow

Transcript

On-screen text reads: "Do Try This at Home from the Institute of Physics. Episode 4: Reversing Arrow"

Camera displays a split screen. On the left side, the on-screen text reads: "Uncle T." 

Uncle T, or Taj, has his webcam switched on and is making a web call. He is sitting down behind a table which has a clear drinking glass on it. Behind the glass there’s a piece of paper showing two hand drawn arrows, pointing in the same direction.  The right side of the screen is blank – there is nothing there.

We hear a dial tone and then the sound of his web call being picked up. His niece appears on right hand of the screen. 

The on-screen text reads: "Saf"

Taj waves at Saf saying "Hello", and Saf waves back saying "Hi". Taj asks Saf, "Ready?"

We hear a swishing noise as the camera cuts to a medium shot of Taj on his sofa. He is on his own now and there’s a table in front of him. On the table there’s an iPad, a marker pen, a clear, empty drinking glass, and a clear glass milk bottle filled halfway with water.

Taj: "Hello and welcome to Do Try This at Home from The Institute of Physics. We’re making these videos for parents and carers across the UK and Ireland so that you can explore science together with your kids at home.

"My name’s Taj and this one’s called Reversing Arrow and I love this one."

On-screen text reads: "Dr Taj Bhutta, IOP School Engagement Manager."

Taj: "Not only is because it’s about light which is my specialist subject but also once you get the hang of it you can really get creative with it." 

Camera cuts to a close-up shot of the items on the table.

Taj: "What you’re going to need is two sheets of paper, a marker pen, a tall drinks glass and some water. First off draw some arrows on the paper. Make them about the same width as the glass."

Taj draws two short horizontal arrows with his marker pen. One arrow is near the top of the paper and one near the bottom, they are directly above each other and pointing the same way.

Taj: "Then fold over the paper to stand your arrows up. Place another sheet of paper in front of it, put the glass in front of that and if you’re doing this with someone in the house it might be useful to set up a chair where they’re going to be sitting." 

Taj folds the sides of the paper over so that he can stand the picture of the two arrows up. He places a sheet of blank paper in front of it and the empty drinking glass in front of the arrows.

Taj: "If you’re doing it over the web, get your webcam ready and position that over here. And then I’m just going to adjust everything, so it’s lined up with the webcam and then fill the glass with water so that the bottom arrow is under the water." 

The webcam is placed at an angle, and Taj adjusts everything to face the webcam. He fills the glass with water to above the position of the bottom arrow. The bottom arrow appears to reverse direction but looks larger than the top arrow and is no longer directly below it.

Taj: "Adjust the position of the glass so that the arrow is about the same size. Hang on, I’m just going to move the arrows back here as well. That looks about right to me. Yes. Then mark the position of the glass using a pen."

As he speaks, Taj adjusts the position of the glass to the right, and then backwards and forwards. He then adjusts the paper away from the glass. The camera shows that there is a small distance between the glass and the paper behind it. At this point the arrows appear to be the same size with the bottom arrow reversed. 

The camera switches to a birds-eye view of Taj tracing around the bottom of the glass on the blank piece of paper, before switching back to a medium shot of Taj again.

Taj: "So now you’re set up. Pour the water away back into bottle, put the glass back into position and then you’re ready to do your trick

"So, I’m just going to call my niece on the webcam."

The camera switches back to the scene we saw earlier. The camera shows a split screen. The on-screen text on the left side reads: "Uncle T."

Taj is calling his niece. We hear a dial tone and then the sound of his web call connecting. His niece, Saf, appears on right hand of the screen.

The on-screen text on her side reads: "Saf." 

Taj waves at Saf saying "Hello", and Saf waves back saying "Hi". Taj asks Saf, "Ready?"

The camera shows Taj sat behind the empty drinking glass and the paper. The two arrows are pointing in the same direction. We hear a drum roll as Taj then pours some water into the glass. As he does so, the bottom arrow flips and points in the other direction. Saf puts her head in her hands and looks amazed.

The camera then switches back to Taj on his sofa. 

Taj: "What’s going on here and how do you explain it to your family? Well, you start with a pencil. A pencil normally looks a little bit like this. We see it because the light bounces off it and travels in a straight line to your eye. Now if I put the pencil in the water, you’ll see that it looks bent because the light changes direction as it travels from the water to the air."

As he speaks, Taj picks a pencil out of a drawer under the table. He holds it upright and uses his other hand to demonstrate the light coming down on the pencil and then heading in a straight line towards the camera. When he puts the pencil in the water, it looks like the top half and bottom half don’t meet up. He again uses his hand to show light travelling down to the glass of water, and then changing direction when it enters and leaves the glass.

The camera switches to a close-up of the paper with the arrows on, and the glass of water.

Taj: "A similar thing happens in a Reversing Arrow trick. Without water in the way we see the arrow as it is. This is because light spreads out in all directions and some of it will travel in a straight line to the webcam over here. When there’s water in the way the light bends.

"The tip of the arrow changes direction here and here and connects at this point before spreading out again. Same thing happens to the light from the tail, connecting at this point. Because the light from the tip is now spreading from here and the tail from here the arrow looks reversed to anyone viewing it from the webcam over here."

As Taj is speaking, he uses his hand to show that some of the light bouncing off the arrow follows a direct path to the camera lens. 

The camera then switches to a birds-eye view of Taj drawing on paper. On one side of the paper, he has drawn an arrow, and on the other side, he has drawn the webcam. He draws straight lines between the arrow and the webcam to show the rays of light travelling to the webcam.

The camera switches to a birds-eye view of the glass with the paper behind it. Taj uses his hand to show the light reaching the glass and then changing direction.

The camera switches to a close-up of Taj drawing again. Taj draws an arrow on one side of the paper and a circle (representing the glass) in the middle of it.  He draws a line from the tip of the arrow to reach the circle.  

Each line that he draws bends inwards as it reaches the circle and bends further as it leaves the circle. The lines cross over at a point between the glass and the camera and spread back out again. Taj shows that the tip and the tail have reversed after this crossover by drawing the arrow in reverse using a dotted line. 

Taj: "Don’t worry if you don’t completely get the science. Enjoy the trick and once you’ve had fun with Reversing Arrow you can also have fun with numbers and letters."

Taj now has a piece of paper with Saf’s name in reverse. He calls out to his niece: "What’s it say, Saf?"

Saf looks confused until Taj places a glass of water in front of it so that it reads her name. Saf looks delighted.

Camera switches to Saf who is pouring water into a jug. Behind the jug is a piece of paper with two fish which are swimming in a different direction. The fish on the top is saying: "Come here!" By the time the water is above the position of the fish at the bottom it changes direction, so that they both appear to be swimming in the same direction.

Taj: "And once your family get the idea they can go off and invent their own version."

Saf raises her arms in the air in victory.

Taj: "Excellent!"

Camera switches back to Taj.

Taj: "If you liked this video give it a like, or why not go over to our website for other things you definitely should try at home. It is goodbye from me and goodbye from Saf."

Camera switches to Saf.

Saf: "Bye!"

Saf waves goodbye.

On-screen text 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."