This document contains teaching notes for a PowerPoint presentation on charging by friction. The presentation is designed to explain the process of electrostatic charging through friction as described in a physics textbook. It includes learning objectives, slides that reveal concepts step-by-step, and concludes by summarizing the key points that students should understand, which are how insulating objects can become charged by rubbing, why they have equal but opposite charges, and that only electrons can move during the charging process.

1. Teacher’s Notes
This sequence of slides is designed to introduce, and explain
electrostatic charging by friction, as explained on
page 242 in New Physics for You, 2006 & 2011 editions
(page 248 in Physics for You, 2001 edition).
Note : When you start this PowerPoint if you see a message about “Read-only embedded fonts” then
you are recommended to select “Open Read-Only” as this (i) gives a clearer font for those at the back
of the room and (ii) ensures that the text-highlighting of key words is correct.
On each slide the key points are revealed step by step, at the click
of your mouse (or the press of a key such as the space-bar).
Before making the next mouse-click you can ask questions of the
class or make statements about what is about to be revealed.
This should help students to become clearer about the ideas involved.
Naturally it pays to have quick practice-run first.
To start the slide-show, press function-key F5
(or right-click->Full Screen)
(to return to ‘normal view’ press the <Esc> key).
For more (free) PowerPoint presentations, visit www.physics4u.co.uk

2. Charging by friction
New Physics for You, p a g e 2 4 2

3. Learning Objectives
Yo u s h o u l d l e a r n :
• H o w in s u l a t e d o b j e c t s c a n
b e c h a r g e d b y f r ic t io n ,
• T h a t t h is is b e c a u s e s o m e
ch arges can mo ve.

4. C h a r g in g b y f r ic t io n
In t h is d ia g r a m :
Th e w o o l a n d
po lyth en e are each
‘u n c h a r g e d ’.
W h a t d o e s t h is
mean ?

5. C h a r g in g b y f r ic t io n
T h e w o o l is +
‘u n c h a r g e d ’, + − −
+
becaus e… + − +
−+−
… it h a s e q u a l − −
amo un ts + + −
o f p o s it iv e a n d −−
n e g a t iv e c h a r g e . + +
Eq u a l n u m b e r s o f
On t h e
+ an d −
po lyth en e
On t h e w o o l

6. C h a r g in g b y f r ic t io n
Eq u a l n u m b e r s o f + +
+ − −
a n u n− o h e t h e w o o l : +
(C o
d t t n m !) + − +
−+−
7+ 7 − − −
+ + −
Eq u a l n u m b e r s o f + −−
+ +
a n u n− o h e t h e
(C o d t t n m !)
po lyth en e:
3+ 3 −

7. C h a r g in g b y f r ic t io n
If y o u r u b t h e w o o l +−
on + − −
+
th e po lyth en e, + +−
s o m e e l e c t r o n s (−) −+
move from the − −
Th e r e a r e n o w m o r e
wool to the + + −−
+t h a n −o n t h e −
po lyth en e.
w o uon lt : t h e m !)
o + +
(C
S o n o w t h e w o o l is c h a r g e d
p o s it iv e l y ,
w it h a s u r p l u s o f 3 +

8. C h a r g in g b y f r ic t io n
Wh a t h a s h a p p e n e d +−
to th e po lyth en e? + − −
+
+ +−
Th e r e a r e n o w m o r e − +
−t h a n +o n t h e − −
p o u n t t heenme!): + + −−
(C o l y t h −
+ +
So n o w th e
p o l y t h e n e is
c h a r g e d n e g a t iv e l y ,
w it h a s u r p l u s o f 3 −

9. C h a r g in g b y f r ic t io n
T h is is s u m m e d
up
in t h e d ia g r a m
o n p ag e 2 42 :
Bo t h o b je c t s
are n o w eq ually
ch arged ,
w it h o p p o s it e
ch arges
becaus e
electro n s −

10. Learning Outcomes
Yo u s h o u l d n o w :
• U n d e r s t a n d w h a t it m e a n s w h e n
a n o b je c t
is ‘c h a r g e d ’ o r ‘u n c h a r g e d ’,
• U n d e r s t a n d h o w a n in s u l a t e d
o b je c t b e c o m e s c h a r g e d b y
r u b b in g ,
• Un d e r s t a n d w h y t h e o b je c t s
h ave eq ual
b u t o p p o s it e c h a r g e s ,
• K n o w t h a t o n l y e l e c t r o n s (−)

11. F o r m o r e d e t a il s , s e e :
 New Phys ics for You, p a g e 2 4 2
F o r m o r e f r e e P o w e r P o in t s , v is it
 t h e w e b -s it e a t www.physics4u.co.uk

12. If y o u a r e c o n n e c t e d t o t h e
w e b a t t h e m o m e n t , c l ic k
b e l o w t o s e e w h a t ’s
a v a il a b l e :
h t t p ://w w w .p h y s ic s 4 u .c o .u k /