RP4-Young's modulus

• Equipment: Metre ruler, steel wire, 1kg masses, mass holder, micrometer.
• Set up: Hang a steel wire off a stand which is clamped to the table, and hang a mass holder off it. Attach a metre ruler next to the wire, and record the original length of the wire. Measure the diameter of the steel wire in multiple areas and calculate a mean.
• Method: Add a 1kg mass onto the holder and record the new length of the wire. Continue to increase the mass until the mass holder is full and then repeat.
• Graph: Plot a graph of mass multiplied by gravity (force) against the extension of the wire. The gradient will be Youngs modulus multiplied by area divided by original length.
• Analysis: The cross sectional area is (pi x d^2) / 4. Youngs modulus is F L/A dl.
• Safety: Wire could snap - wear goggles; masses could fall - add padding beneath; stand could topple - use a counterweight or clamp.
• Alternative experiments: Attach two wires next to each other - one with a main scale and the other with the masses and a vernier scale. In this experiment, the other wire compensates for any sagging or thermal expansion affects.