Rollerblades and chalk: Quantitative Observational Experiment

Aim

To establish an understanding of how to characterise the motion of Eugenia's hand relative to the camera and relative to her and a rule to move between these two frames of reference

Prior Knowledge

• Vector addition
• Theorem of Pythagoras

Description of the Experiment

Eugenia skates past a chalkboard raising her arm straight up and putting marks on the board every half second. Observe her motion with respect to the board; the motion of her hand with respect to her body, and the motion of her hand with respect to the board. Play the video frame by frame to determine the speeds of these three motions. See data analysis example

Youtube movies can be stepped frame by frame using the , and . keys on your keyboard. If you want to download the movie to your computer, right-click or control-click HERE.

Questions

1. What is the direction of Eugenia's motion? What is the direction of the chalks motion? When answering these questions, remember that motion is relative, and you need to consider different observers.



2. Can you figure out how fast Eugenia was moving with respect to the board?



3. Can you figure out how fast Eugenia's hand was moving with respect to her?



4. Can you figure out how fast Eugenia's hand was moving with respect to the board?



5. Is there a relationship among your answers?