Impress your friends and family with this floating image – a modern take on an old-timey magic trick.
You will need
- Clear plastic dome from a frozen drink or smoothie
- Thin plastic container with flat lid (we used a blackberry punnet)
- White paper
- Pencil
- Permanent marker
- Good pair of scissors
- Clear tape
- Smart phone with internet
- Room where lights can be dimmed.
Safety
Be careful with the cut edges of plastic, they can be sharp. This activity requires using the internet and YouTube. Ask an adult to supervise these steps. If you ever feel unsafe on the internet, let an adult know.
What to do
Wash your plastic frozen drink top and dry it.
Peel off any stickers from your clear plastic container, wash it, dry it and cut the lid off.
Place your sheet of paper on a table. Hold the plastic dome sideways over the paper.
Using your pencil, trace the dome outline of the drink top onto the paper. You should get a half circle.
Cut out the paper half circle.
Test to see if your paper half circle fits inside your drink top. You might need to trim the paper until it fits snugly inside the dome and no parts hang out of the bottom.
Place your paper half circle on the flat portion of the clear plastic lid. Use a permanent marker to trace the paper half circle onto the plastic.
Cut out the plastic half circle. Check that it fits in the dome snugly like the paper did.
If your drink top has a flap for the straw, fold it up so it’s no longer covering the opening.
Tear a small piece of tape and use it to stick the top of the plastic semicircle to the top of the dome.
Tear another piece of tape. Next tilt the plastic inside the drink top so that it makes a 45-degree angle with the rim. Use the tape to secure it in place.
Turn the screen brightness all the way up on the smartphone and then navigate to this video. Have an adult supervise this task.
Place the drink top on top of the smartphone so that the plastic slants away from you.
Dim the lights of the room and get eye-level with the drink top. What do you see?
With an adult, explore other videos to view in your contraption. We recommend searching for ‘black background’ plus whatever you want to see.
What’s happening?
A stage setup for Pepper’s ghost. Credit: Wikimedia Commons / Bertrand
Before modern technology and special effects, people had to get creative to make supernatural events seem real. Pepper’s ghost is one creative theatre trick that dates to 1862. It’s named after a scientist called John Henry Pepper who made the special effect famous in a play called The Haunted Man and the Ghost’s Bargain (they really needed a ghost!).
In the stage version of this trick, an actor dressed as a ghost stands in a room below the stage. A clear pane of glass is set at angle above the actor. This actor is brightly lit so that light bounces off the actor and then reflects off the glass towards the audience. This makes a ghostly image appear on stage. Just like how the flat video you had on your smartphone appeared inside of the plastic drink top.
Why does the light reflect off the glass or plastic? When light traveling through air hits glass or plastic, it slows down ever so slightly. This happens because the new material is denser – it packs in more atoms than air. The change in speed causes some of the light to reflect off the new material. The reflection works best at just the right angle, so try moving around your experiment to find the best viewing spot!
Is this a hologram?
Sadly, no. A hologram is a 3D “photograph” that you can walk around and see from all angles. This usually requires lasers and special mirrors. If you walk around your Pepper’s ghost, the video is still 2D. You’ll also notice that the image disappears and is best seen from one angle. While it may look like a hologram, Pepper’s ghost is better described as an illusion or a theatre trick.
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