What it shows
The holding force of an adhesive tape is proportional to the area stuck down, so doubling the overlap should double the load it takes before peeling. You test the idea with strips and small weights and plot a graph.
The science
Tape sticks because the adhesive molecules attract the surface across the area of contact. The holding force is therefore roughly proportional to the contact area, if the width is fixed. In a lap joint under a pulling load the peel and shear forces are not perfectly even, so real graphs bend a little at long overlaps.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A roll of transparent sticky tape
- Two flat plastic or steel rulers, or card pieces
- A small plastic bag as a hanger
- Marbles or coins as weights
- A kitchen scale
- A ruler
- Graph paper
Safety
For this project: Weights must hang low so they do not fall on feet. Keep scissors in the care of an adult.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
Step by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut strips of tape each 2 cm wide, if the tape is wider, and lay them down with an overlap of 1, 2, 3, 4 and 5 cm joining two card strips end to end.
Rub each overlap firmly with a spoon so that pressure is the same for all joints.
Hang one card strip from a clip fixed on the edge of a table.
Hang the bag from the other strip and add marbles one at a time, gently.
Note the mass at which the joint pulls apart.
Repeat three times for each overlap length and take the mean.
Plot a graph of overlap length against breaking load and describe the shape.
What you should see
The breaking load rises steadily with overlap length, and the graph is nearly a straight line through the origin for short overlaps. It bends for longer overlaps.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01What does a straight line graph through the origin mean?
The two quantities are proportional.
02Why rub the tape firmly?
It improves contact, giving a fair test.
03What kind of force holds the joint?
Adhesion between the glue and the surface.
04Why repeat three times?
To cut random errors and find an average.
Take it further
Test the load for peeling at an angle compared with pulling along the strip.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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