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Newton's Second Law

By | October 2010
Page 1 of 3
Given below is a strobe picture of a ball rolling across a table. Strobe pictures reveal the position of the object at regular intervals of time, in this case, once each 0.1 seconds.  

Notice that the ball covers an equal distance between flashes. Let's assume this distance equals 20 cm and display the ball's behavior on a graph plotting its x-position versus time.  

The slope of the position versus time graph shown above would equal 20 cm divided by 0.1 sec or 200 cm/sec. The following graph displays this exact same information in a new format, a velocity versus time graph.  

This graph very clearly communicates that the ball's velocity never changes since the slope of the line equals zero. Note that during the interval of time being graphed, the ball maintained a constant velocity of 200 cm/sec. We can also infer that it is moving in a positive direction since the graph is in quadrant I where velocities are positive.  

To determine how far the ball travels on this type of graph we must calculate the area bounded by the "curve" and the x- or time axis.  

As you can see, the area between 0.1 and 0.3 seconds confirms that the ball experienced a displacement of 40 cm while moving in a positive direction.  
Physics Lab
Motion of a Motorized Cart

* To study the motion (position, displacement, velocity, and acceleration) of a motorized cart. * To practice constructing position vs. time and velocity vs. time graphs for a motion.

constant velocity motorized cart| meter stick or metric tape| about 2 meters of ticker tape| graph paper|
masking tape| stopwatch or watch with a seconds hand|
data table| grading rubric|

In this lab you will observe and measure the motion of a motorized cart by marking its position along a strip of tape at regular time intervals. Note that you can adjust the speed of the cart using the small dial - find a speed that works well for you and then do not...

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