Electrostatic Forces

51

Electric Forces

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Electric Forces

Some text here about the topic of discussion

52

There is one very common way we can see forces between charged
objects. You can see it in the picture of the boy below. You might
also experience it when you take clothes out of a dryer.
What is it?

Click here to launch a simulation to explore
charging and forces between charges

Forces Between Charged Objects

by static electricity (static cling)

53

In the activity where you
had a balloon and a
sweater, what happened
when you rubbed the
balloon on the sweater and
then let it go?

Just like we saw with masses, forces are exerted between charges!

This is called Coulomb's Law!

Coulomb's Law

Opposite charges ATTRACT each other.

Same charges REPEL each other.

Multiple Choice

Like charges ______________.

• repel

• discharge

• attract

• don't attract or repel

Multiple Choice

Opposite charges repel. ______________.

• True

• False

54

20 Opposite charges repel.

True

False

Answer

*not in notes but good practice*

Multiple Choice

An electron and a proton are attracted to each other.______________.

• True

• False

55

21 An electron and a proton are attracted to each
other.

True

False

Answer

*not in notes but good practice*

Multiple Choice

What types of charges attract?

• Positive and Positive

• Positive and Neutral

• Negative and Neutral

• Positive and Negative

56

The interaction between charged
objects is a non­contact force that
acts over some distance of
separation. We call this an
electrostatic force.

Unlike Charges Attract!

Opposite Charges Repel

Click here to see a video on Fun with Static
Electricity

Electrostatic Force

57

Electrostatic Force

1) Charge of the Objects

2) Distance between the 2 objects

There are 2 main factors which
play into electrostatic forces.

What other force does this remind you of?

58

Forces between like charges

As the amount of charge increases, what happens to the magnitude
(strength) of the force?

+1

+1

+2

+1

the strength of the force also increases

59

+1

+1

+2

+1

We observe that the force of repulsion doubles when one
of the charge doubles.

Electrostatic Force

Therefore, electrostatic force is DIRECTLY proportional to the

amount of charge present.

61

The Electrostatic Force
direction between 2
charged objects is
proportional to the
product of their charges.

Charge
1

Charge
2

Sign of
Product
Type of force felt

+

+

+

Repulsion

­

­

+

Repulsion

+

­

­

Attraction

Electrostatic Force

62

As the charges move farther apart,
the force between them is decreased.

What do you think happens to the force between
charges when we move them father apart?
Talk about this at your table.

+

+

d

Slide for the answer!

Discussion Question

it will decrease!

63

Force between charges
reduces as the charges move
apart.

Does this graph look familiar?

Electrostatic Force

64

Putting it all together

The Electric Force between 2
charges is directly proportional to
the amount of charge!

It also decreases in strength as the
charges move farther apart.

Multiple Choice

As the amount of charge increases, the force between the charges __________.

• decreases

• stay the same

• increases

65

23 As the amount of charge increases,
the force between the charges __________.

A

decreases

B

stay the same

C

increases

Answer

directly proportional

Multiple Choice

As the amount of distance between charges increases, the force between the charges

• decreases

• stay the same

• increases

66

24 As the amount of distance between charges
increases, the force between the charges
__________.

A

decreases

B

stay the same

C

increases

Answer

inversely or indirectly proportional

67

How is Coulomb's Law (forces between charges) similar/different to
Newton's Law of Gravitation (forces between masses)?

Similarities

Differences

Answer

-Both depend on two factors:

size and distance

-Both get stronger when size

increases (mass or charges)

-Both get weaker when distance

increases

-Both are non-contact forces

(field forces)

Coulomb's Law deals with

charges (positive, negative, or
neutral) while gravity does not

Charges can attract or repel,
but gravity CAN ONLY
ATTRACT