Eric Murray, Spring 2006
Question these experiments will enable you to answer: Is the mechanical energy of my system constant?
Features: The object is a cart on an inclined track (a one-dimensional space). Automated measurements are made with a device that is interfaced to a computer and provides real time graphs of the motion. The cart is given a brief push, so it rolls up the incline to a stop, and then rolls back down. With the position and velocity of the cart measured by the motion sensor, the kinetic energy and gravitational potential energy can be calculated.
Preliminaries: Make sure the motion sensor is plugged into channels 1 and 2. Open the data template. You'll find graphical displays for position and velocity as a function of time. The sensors have been set to record data at 50 Hz, for 8.0 s, beginning 1.0 s after Start
has been clicked. The position and velocity of any point on the graph can be displayed with the Smart Tool
(cross-hairs).
Experiment 1: Level the track. This can be done by gently rolling the cart each direction, and seeing if the motion is the same each way. Use the high riser to incline the track so the motion sensor is at the high end. Record the height of the riser, and the distance between the track supports. With the cart at the end of the track away from the motion sensor, click Start
, and give the cart a brief push, so it rolls up the incline to a stop, and then rolls back down. Make sure the cart does not come within 15 cm of the motion sensor.
Record the position and velocity at six times spread roughly evenly through the valid data. The times will not be exactly the same on the position and velocity graphs, but they will be very close. Be consistent in how you record the time. Let the zero of gravitational potential energy be at the minimum position
, that is, where the cart comes to a stop at its highest point. Calculate the kinetic energy of the cart, the gravitational potential energy of the Earth-cart system, and the mechanical energy of the Earth-cart system at each time. Find the average, the standard deviation, and the standard error in the mechanical energy. You may find an Excel spreadsheet to be helpful.
Experiments 2: Repeat experiment 1 with one mass block added to the cart.
Experiments 3: Repeat experiment 1 with two mass blocks added to the cart.
Summary: Review your worksheet. Think about the goals of these experiments, your results, and the expectations from theory while writing your discussion.