Physics 105

February 24, 2003

The motion we observe is always a result of forces acting on the objects in motion. Sometimes these forces are clearly present, like for example a horse pulling a cart, while in other cases we do not observe the forces directly but instead only observe their effect, like for example the force of friction. Experiments have shown that the acceleration of an object is directly proportional to the force acting on the object (please refer to the note "Force and Motion").

Today we will continue a series of measurements in which we look at acceleration. An object accelerates when its velocity changes. A common mistake made by students trying to understand acceleration is that positive acceleration is associated with positive velocities while negative acceleration is associated with negative velocities. Today we will show that the sign of the acceleration is not related to the sign of the velocity of an object.

• Carry out experiment P10 to see how the acceleration of an object changes when you change the force acting on it. In this experiment we will be using the motion sensor to measure the velocity of the car.

Note: in this experiment you will be comparing the results of a series of measurements with a theoretical prediction. In making this comparison it is very important to determine the errors in your experiments to be able to judge whether or not the observed difference between theory and experiment is significant. In addition, of the theory predicts that the outcome of the experiment is independent of for example the mass of the cart, you will need to verify this prediction.

Next weeks lab report needs to focus on the scientific method, and describe experiment P04, P09 and P010. In each case a detailed comparison must be made between the results of the measurements and the theoretical predictions. Any deviations should be compared with the estimated errors.

© Frank L. H. Wolfs, University of Rochester, Rochester, NY 14627, USA

Last updated on Tuesday, February 18, 2003 14:48