Electrical Charge and Non-Contact Forces
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Non-contact forces result from interactions between two objects that are separated by some measure of distance. Examples of non-contact forces include gravitational force, electrostatic force, and magnetic force.
Inverse Square Forces
An inverse square force is a force that is inversely dependent on the square of the distance between the interacting objects:
F∼1
2 Where: F=force, r=distance
This type of force is strong at close range, but rapidly weakens as the distance between the objects increases. While the force may become so small that it is essentially negligible at very large distances, an inverse force is never zero. This means that no matter how great the distance, the force always exerts some influence upon the objects.
Electrostatic Force is a non- contact, inverse square force.
Electrostatic force, given by Coulomb’s Law is directly proportional to the product of the absolute value of two charges, and is inversely proportional to the square of the distance between the charges. The value of Coulomb’s constant depends on the medium in which the charges are located. For air, k is approximately 9 x 109 N m2/C2.
Gravitational force is another non- contact, inverse square force.
Gravitational force is directly proportional to the product of the masses of the objects and is inversely proportional to the square of the distance between them. In standard units, the gravitational constant, G=6.67 x 10-11 N m2/kg2.
Graphing Coulomb Force
The table below shows the electric force (F) between 2 point charges as it changes with the distance between them (d).
Set numbe
Distance(m)
Force (N)
1
0.05
0.00389
2
0.06
0.00339
3
0.08
0.00229
4
0.11
0.00129
5
0.17
0.0004
6
0.2
0.00037
7
0.22
0.00023
8
0.24
0.00022
9
0.27
0.00019
10
0.31
0.00016
1. Plot distance in meters on the horizontal axis and force in Newtons on the vertical axis. Add a trendline to the graph: if using software, add a “power” trendline; if drawing by hand, draw a curved line through the points. From the “Trendline options” choose “Power” since this is a 1
2 function.
2. Include labels for each axis and a title on the graph.
3. Insert the graph below:
Questions:
1. Consider Coulomb’s law and a pair of values (d, F) and calculate the product of the 2 charges.
2. Consider x= 10cm and the co
esponding force value. How far the objects should move for the force between to double?
3. Consider x= 10cm and the co
esponding force value. How far the objects should move for the force between to halve?
4. What are the similarities and differences between the electrostatic force and gravitational force? Consider the type of interactions not just the mathematical equations.
Problems:
-Include the drawings as pictures or you can use the word features, Insert—Shapes—Line and/or a
ow.
-Label the forces according to the names of the charges for q1 and q2 the pair of forces is F12 and F21.
1. A long a right line there are 3 identical charges, q1>0 and q2< 0, q3<0. Draw the forces on the middle charge (q2) due to the other 2 charges.
1. In the vertices (tips) of a right triangle there are 3 identical charges (q1>0 and q2< 0, q3>0). Draw the forces on the right angle charge due to the other 2 charges. The a
angement of the charges is your choice.