How to Make a Magnetic Spring Scale

Hang the spring off the end of a laboratory stand. Measure the length of the spring with no weights attached. Attach a single 100g weight, and measure the extension of the spring. Repeat the length measurement with 200g and 300g placed on the end of the spring. Plot the extension of the spring as a function of weight. A straight line graph should be obtained as stated by Hooke's law: F= -kx. In this equation F is the force on the spring, k is the spring constant, and x is the spring extension. The gradient of the graph is equal to the value of the spring constant. Calculate the gradient. The gradient is equal to: Max weight - min weight / max extension - min extension. The spring is now fully characterised.

Remove the weights from the spring. Using the hammer and nails, secure the spring to the wooden board horizontally, so that its long axis is parallel to the plane of the board. Tape the ruler below the spring so that its long axis is parallel to the long axis of the spring. The ruler will act as a scale so that the extension of the spring can be measured. The magnetic spring scale is complete

Bring the second permanent magnet into close proximity (approximately 6cm) with the magnet mounted on the spring. Orient the free magnet so that there is an attraction between the two magnets. As the magnets are attracted, the spring should extend. Measurement of the extension, using the ruler, allows the force to be calculated using Hooke's law and the value of the spring constant determined earlier.