What’s the magic effect?
This amazing science demonstration appears like you can move a straw with the power of your mind.
You will need:
- A drinks bottle
- A plastic straw (I find McDonald’s straws work best. Subway straws don’t work at all.)
What’s the method?
The straw is moved by electrostatic attraction. Before balancing the straw onto the bottle lid you have secretly charged it up with ‘static electricity’. This can be done with a cloth rag or fleecy jumper. Squeeze down hard on the end of the straw through the material and pull the cloth along the length of the straw in one fast motion. The straw should be now charged. Carefully balance the straw on the bottle lid. This is harder than you might think as the straw is already being attracted to your fingers. Try to minimise the amount of time you handle the straw as you don’t want the straw to lose its charge. Now if you place your finger close to the end of the straw (as shown in the photo), the straw will start rotating and moving towards your finger. It looks very spooky!
Here’s another really simple science magic trick that you can make with easy to find objects. You will need:
- Plastic drinks bottle.
- Vinegar sachet (From my experience the Heinz Malt Vinegar sachets work best. They can be bought in bulk from catering suppliers if you wish to do this as a class activity.)
The first thing you need to do is adjust the weight of the vinegar sachet so that it only just floats on the surface of the water. Some sachets will sink with no added weights, unfortunately you will have to find another one. Now add paper clips until the sachet is weighed down enough so with a light push it will sink. It’s best to do this in a sink or bucket of water, as if you do it in the bottle you’ll spend ages trying to fish the sachet out of the bottle each time you make an adjustment.
Now add the sachet to the drinks bottle and fill the bottle with water until it spills over the top. Screw the lid on tightly. If there are any air bubbles on the side of the vinegar sachet, hit the bottle hard to dislodge the bubbles.
Now for the magic. If you squeeze the side of the bottle the vinegar sachet should sink like a submarine. Release your tight grip and the sachet will float. If you disguise the squeezing you can give the illusion of telekinetic powers.
So what’s the science? Well… liquids are hard to compress unlike gases. When you squeeze the bottle it causes the small amount of gas at the top of the vinegar packet to compress. The volume of the vinegar sachet decreases. As the mass doesn’t change, the result is that the sachet’s density increases. (Density = Mass/Volume) The density is now greater than the surrounding water and so the sachet sinks. Releasing the squeezing pressure allows the gas to expand and the sachet’s density to become less than the surrounding water and so it floats again.
I created this prototype illusion a couple of years ago.
I spent last Saturday with Paul Daniels hearing him tell stories and pass on his many years of performance experience. It was a wonderful day learning about both the show and the business sides of show business. Lots of ideas were added to my notebook which is always a good sign.
This will take 5 minutes to make with simple to find materials. You need the following:
- A sweet or biscuit tin. Mine has a 23cm diameter and a depth of 7cm.
- Rubber sheet
- 20x Coins or washers. Alternatively use a metal weight.
Put the coins/washers into a stack and run some tape around the diameter to make a counter weight. Tape this stack of coins onto the inside edge of the sweet tin. (You may want to line the weight up with the seam of the tin to help identify it’s position when looking on the outside.) Now add the rubber sheet to the outside perimeter of the tin and tape it down. The rubber sheet provides grip for the tin when on the ramp. Your construction should look like the photo below.
Place the “antigravity tin” on a ramp with the counter weight on the up hill side (see photo below). You will need to experiment to find the best incline. Let go of the tin and it should roll up hill giving the illusion of defying gravity. That is until the counter weight rolls around until it reaches the bottom of the tin.
The added weight changes the centre of mass (COM) of the tin which would normally be at the centre of the cylindrical tin. The COM is now situated close to the extra weight on the edge of the tin. Gravity acts on the COM and pulls it downwards. In order for the COM to move downwards, the tin has to roll up hill. Physics and not magic.