Topic outline
ACTIVITY DESCRIPTION
The ultrasonic position sensor is exploited to measure the period of the harmonic motion for a spring-mass system. If the spring constant is known the system can be used for mass measurement, if the mass is known the spring constant can be characterized.
Use position measurements from the ultrasonic sensor to determine the oscillation period of a mass hung from a spring.
FIRST VERSION
In the following, first we list the simple steps need to play the activity in its basic form. You may arrange the equipment and decide which measurements your students will have to perform, i.e. build your own "Learning scenario” suitable to your students age and background.
Later we suggest a more complete scenario, suitable for 14 to 14-years old students and shows the results.
- Hang a spring over a proper support and attach a mass to it. Start an oscillatory motion.
- Place the mBot ultrasonic sensor below the spring in upward vertical position, so that the ultrasonic sensor see the mass (eventually enlarge the mass surface by a cardboard).
- Press the on board button to start measurements. The oscillation period is shown on the led display and the spring constant can be evaluated.
- Discuss the importance of such a relatively simple phenomenon through the dedicated supporting material (see attached presentation).
SECOND VERSION
According to Hooke's law, elastic forces are proportional to the spring elongation through a coefficient called the elastic constant k. For a vertical spring-mass system in equilibrium conditions, the mass itself then results proportional to the elongation and to the constant. Therefore by hanging known masses to the spring and measuring the elongation it is easy to evaluate the spring constant.
The idea for the experiment was to measure the spring elongation for three different masses and estimate the spring constant as an average from the three measures.
ACTIVITY RESOURCES
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