Standing waves on a string experiment (part 1)

Using elastic cord ....

First, measure some properties of the elastic cord. You'll need to include uncertainties in just about every quantity.

First, make all these measurements.

1. Cut a piece of stretchy cord roughly 170 cm long. Measure the length L_tot and mass m of this cord carefully. Include uncertainties in each quantity.
2. Place the cord onto the table, under no tension but aligned as straight as you can make it. Place two marks onto the cord, separated by about 50 cm. Measure the distance between these marks, L₁, and its uncertainty.
3. Hang a mass of M = 650 g by the cord over the pulley. Once again, measure the distance between the two marks, including an uncertainty. Call this L₂.

Next, do some calculations.

4. Compute the linear mass density μ (kg/m) of the cord. Include an uncertainty.
5. Compute the linear mass density μ_s of your cord when it is stretched and holding 650 g. Include an uncertainty.

Preparing for the next class

• Arrange for one student to take your piece of stretchy cord away at the end of class; you will need to bring it back to use next time.
• Compute the speed of waves travelling down the stretched cord, and an uncertainty in that speed.