Force-Time Graphs
A force-time graph will have force (N) on the vertical axis and time (s) on the horizontal. The area under a force-time graph is Ft, which is the impulse the object will experience during that time interval (I=Ft). Recall that impulse is equal to the change in momentum of an object.
Example 1:
The force acting on an object over a 15 second interval is shown below:
a) Determine the force acting on the object at t=5 seconds:
At t=5 seconds, F=4N
b) When was a constant force acting on the object:
Between t=0-3s and t=7-12s
c) Calculate the total impulse acting on the object over the 15 second interval:
The total impulse acting on the object = the area under the graph. It is convenient to divide the graph into several rectangles and triangles and then calculate the sum of these areas:
Area A = 2\times 7=14
Area B = \cfrac { 1 }{ 2 } \times 4\times 4=8
Area C = 5\times 6=30
Area D = \cfrac { 1 }{ 2 } \times 3\times 6=9
Total area = 14+8+30+9= 61
Therefore, Impulse, I=61Ns