Tensile strength is the largest amount of force that can be applied to an object being stretched or pulled until it breaks. Tensile strength can be a useful property of a material. For example, fishing line can be pulled hard by a large fish swimming away without breaking. Some things, however, like rubber bands, have good tensile strength but can deform or snap easily. Deformation is the change in the original size or shape of an object.
Measure the tensile strength of various materials.
- Fishing line
- Garbage bag
- Rubber band
- Plastic wrap
- Strand of hair
- Spring scale gauge
- Notebook and pen
- Any other material you would like to test
- Tie a short length of your test material in a secure knot around the hook of the spring scale.
- Secure the top of the spring scale to something steady, like a table or wall.
- Pull on the test material until it breaks. Keep an eye on the spring scale reading. (Depending on your spring scale, some of your test materials may not break before the spring scale breaks. Be careful!)
- Record the force measured by the spring scale right before the test material breaks.
- Compare results.
Fishing line will have the greatest tensile strength, while hair will have the weakest.
Tensile testing is often used to determine whether or not a material will be useful for a given purpose, such as catching a fish, or building an airplane. Many objects obey Hooke’s Law, F = kx (where F is force needed to extend or compress, x is distance of extension of compression, and k is stiffness), which is a description of force for springs, but also applies well to many elastic objects (objects that can be stretched). This means the force applied to an object (in our experiment, the force of pulling), is proportional to the change in the length of the object, until it deforms or breaks.