Runaway Train: Investigating Speed with Photo Gates
Students conduct an experiment to determine the relationship between the speed of a wooden toy car at the bottom of an incline and the height at which it is released. They observe how the photogate-based speedometer instrument "clocks" the average speed of an object (the train). They gather data and create graphs plotting the measured speed against start height. After the experiment, as an optional extension activity, students design brakes to moderate the speed of the cart at the bottom of the hill to within a specified speed range.
Engineers create safe and fun machines through testing smaller models and prototypes of their designs and drawing conclusions from the testing results.Copyright 2012 Polytechnic University at NYU
Motion of an object subject to the acceleration of gravity is a fundamental study in engineering mechanics. Engineers use the concept of potential and kinetic energy to solve real-world problems in design and analysis of dynamic systems. The student experiment is designed to inspire questions about how gravity affects the speed of objects that are free to roll or slide down inclines and develop an engineering intuition through observations of the experimental procedure and measurement data. In the design-oriented extension to design a train brake that controls the final speed to within a specified range, student designs are limited only by the material availability and speed constraint, with the goal to produce creative braking systems that result in comfortable forward car speeds.
After this activity, students should be able to:
- Describe how kinetic and potential energy is related to the speed of a rolling car on a hill.
- Describe the points of highest potential and kinetic energy given a two-dimensional path of a cart.
- Name the units used for speed measurement (meters per second).
- Predict the speed of an object that is dropped from doubling the height of drop, given the speed at the original height.