How to Do the Invisible Glass Rod Trick

Are there any objects invisible in reality? This Invisible Glass Rod will teach you how to make an object disappear. Sound crazy, isn’t it? Everyone can do it at home with household materials.

Age: 3+        Time: <10min

 Safety 

1. Adult supervision.

2. Be careful with the fragile glassware.

3. The oil can make the floor very slippery.

 Materials List 

• Cooking oil
• Water
• Glass rod
• Glass jar (or other transparent containers)

 Instruction 

Step 1/3 – Add about 40ml water to the glass jar.

Step 2/3 – Add about 40ml cooking oil on the top of the water.

Step 3/3 – Put the glass rod into the jar, you can find that the part of the glass rod in the cooking oil disappears.

 Troubleshooting 

Why the daily used glassware cannot have this effect?

—Different kind of glassware has different refractive indices. We need the high borosilicate glass in this experiment, such as beakers and grass rod.

 Scientific Description 

When light travels from one transparent medium into another, the direction of propagation generally will change. This phenomenon is called the refraction of light. the refractive index or index of refraction of a material is a dimensionless number that describes how fast light travels through the material.  The higher the refractive index of the material, the stronger the ability to refract light. When the refractive index of the two materials is different, the light will travel in a different direction in them. The refractive index of the glass is greater than the refractive index of water so the boundary between the beaker and the water can be clearly seen. When two transparent stuff shares the same refractive index, the direction of the traveling light in them is the same so when one is placed in another one, the boundary disappears and that is why it comes to disappear. In this experiment, the refractive index of the oil is almost the same as that of the glassware, when the glass beaker is placed in the oil, the boundary is almost invisible. That is why we can see the glass rod in the water but cannot see it in cooking oil. The glass rod and the pipette in the oil share this invisible magic.

 Extensions 

Put the glassware such as the beaker in the oil in advance, and then take out the pieces one by one. That is what magic does.