Suppose two socks acquire the same charge. do you think they would stick together? explain:

Name: ______________________________________Date: ________________________ 

Student Exploration: Coulomb Force (Static)

Vocabulary:

 Coulomb’s law, electrostatic force, vector 

Prior Knowledge Questions

(Do these BEFORE using the Gizmo.)Have you ever taken clothes out of the dryer and found a sock stuck to your underwear? Static cling is an example of

electrostatic forces

, or the forces that exist between charged objects.1.How do you think the sock and underwear became charged? The sock and the underwear became charged because they have different charges.2.Suppose two socks acquire the same charge. Do you think they would stick together? No_ Explain: _Because they would repel each other since they have the same charge. ____ 

Gizmo Warm-up

 As clothes are tumbled in a dryer, electrons are rubbed off some items, giving them a positive charge,and deposited on other items, giving them a negativecharge. These charged items exert electrostatic forces on one another. You can explore these forces with the

Coulomb Force (Static)

Gizmo™. In its initial settings, the Gizmo shows two objects that each have a charge (

q

) of 10.0 × 10

-4

 C (coulombs). Turn on the

Show force vector 

 checkboxes for objects

A

 and

B

. The arrows coming from each object are

vectors

 that represent the electrostatic force. The direction and length of each vector show the direction and magnitude (strength) of each force.1.Are the vectors for objects

A

 and

B

 pointing together or away from each other? _Away_ 2.Are objects

A

 and

B

 attracted together or repelled apart? ___________________________ 3.Compare the lengths of the vectors. What do you notice? ___________________________  _________________________________________________________________________ 

Activity A: The effect of charge

Get the Gizmo ready:



Turn on

Show grid

. Place object

A

 on the

 x 

-axis at-5 and object

B

 on the

 x 

-axis at +5.



Check that

Show force vector 

 is turned on for each object.

Question: How does charge affect the strength of the electrostatic force?1.

Observe : You can change the charge of each object by entering the desired value in the

q 

 A

 and

q 

B

 boxes. Observe the force vectors for each of the situations listed in the table below. Based on the force vectors, state whether the objects are repelled from one another, attracted to one another, or if there is no force at all.

q 

 A

 q 

B

Attraction, repulsion, or no force?

1.0 × 10

-4

 C1.0 × 10

-4

 C

Repulsion

-1.0 × 10

-4

 C1.0 × 10

-4

 C

Attraction

-1.0 × 10

-4

 C-1.0 × 10

-4

 C

Repulsion

1.0 × 10

-4

 C0.0 × 10

-4

 C

No force2.

Make a rule : Complete the following sentences with the words “attract,” “repel,” or “zero.”

When the charges are the same, the two objects

repel

one another.When the charges are opposite, the two objects

attract 

 one another.When one of the objects has no charge, the resulting force is

zero.

3.

Predict : How do you think the magnitude of the electrostatic force between two objects will change if the charge of each object was doubled?

The magnitude of the electrostatic force would be doubled which would make in increase.4.

Measure : Turn on

Show vector notation

 for both objects. Set the charge of objects

A

 and

B

 to 1.0 × 10

-4

 C. The force on object

A

 is now -0.90

i

 + 0

 j

 N. That means that the force is -0.90 N in the

 x 

 direction and 0 N in the

y 

 direction.

A.

What is the magnitude of the force on object

A

? |

F

A

| =

0.90iB.

What is the magnitude of the force on object

B

? |

F

B

| =

0.90iC.

The force on object

A

 is negative. What does this indicate about the direction of the force? _ 

It’s going in the opposite direction

. ______________________ 

(Activity A continued on next page)Activity A (continued from previous page)5.

Gather data : For each charge combination listed in the table below, write magnitude of the force on object

A

. (Note: The magnitude of the force, or its strength, is always positive.)

q 

 A

 q 

B

|

F

A

|

Factor 

 q 

 A

 ×

q 

B

1.0 × 10

-4

 C1.0 × 10

-4

 C

0.90N11E-8

1.0 × 10

-4

 C2.0 × 10

-4

 C

1.80N22E-8

2.0 × 10

-4

 C2.0 × 10

-4

 C

3.60N44E-8

2.0 × 10

-4

 C3.0 × 10

-4

 C

5.40N66E-86.

 Analyze : What patterns do you notice in the data?

The factor and the qa and qb are the same.

7.

Calculate : To calculate how much the force is multiplied, divide each force by the first value, 0.90 N. Fill in these values under

Factor 

 in the table. What do you notice? _ 

that the factor increases by 2.

8.

Calculate : Calculate the product of the two charges, and fill in these values in the last column. Compare these numbers to the

Factor 

 numbers.What do you notice? _ 

the factor is in front of the product.

  _______________________________________________________ 

9.

 Apply : What would you expect the force to be if the charge of object

A

 was 5.0 × 10

-4

 C and the charge of object

B

 was 4.0 × 10

-4

 C?  _ 

18N

 _______________________________________ Check your answer with the Gizmo.

10.

Challenge : Based on what you have learned, write an equation for the strength of the electrostatic force for two charges that are separated by 10 meters. Use the Gizmo to check your equation.

F= 9x10 

7 

 (q

 A

+q

B

)

Activity B: The effect of distance

Get the Gizmo ready:



Turn on

Show distance

.



Set

q 

 A

 to 10.0 × 10

-4

 C and

q 

B

 to 1.0 × 10

-4

 C.

Question: How does distance affect the strength of the electrostatic force?