Robot Arm Waves: Amplitude, Energy and Wavelength

Team Report: The Wave-Making Robot

1The Gearhawks, the robotics team at Northfield Middle School, were asked to build a demonstration for the school's STEM night. Team captain Adaeze Moreau suggested using the robot's arm to make waves. The team stretched a long coiled spring 6.0 m across the gym floor and clamped the far end to a heavy table leg. The robot's gripper held the near end of the spring and swung it from side to side, sending waves along the coils.

2Two settings in the robot's program controlled the waves. The motor setting chose how many side-to-side swings the arm made each second, which is the frequency of the waves in hertz (Hz). The swing setting chose how far the coils moved sideways from their resting line, which is the amplitude, measured in centimeters. Programmer Bao Tran placed tape marks every 20 cm along the floor and filmed the spring from above. In slow motion, the team measured the wavelength, the distance from one crest to the next.

3The team kept the amplitude at 10 cm and tested four frequencies. The results are in the table. Before the battery ran low, they also timed single waves: a wave with an amplitude of 5 cm and a wave with an amplitude of 20 cm each took 2.5 s to travel the 6.0 m spring.

4To find out how much energy each wave carried, the team used a computer model of their spring. The model gave the energy carried by one wave in millijoules (mJ) for three different amplitudes, all at a frequency of 2 Hz. The bar graph in Part 2 shows the model's results. Adaeze wants the final demonstration to knock over a foam block at the far end of the spring.