2
PHYS 1L03, Winter 2009, McMaster University, R.Nejat
What is going on in this picture?
Force
PHYS 1L03, Winter 2009, McMaster University, R.Nejat
• When you kick a ball, your foot exerts a force
on the ball while the two are in contact
1
,
changing the velocity
2
(the speed and/or the
direction) of the ball.
•
1
:--
Force is an interaction between two
objects
.
•
2
:--
Force (external) changes the velocity,
causes acceleration
, of the object.
Force:
PHYS 1L03, Winter 2009, McMaster University, R.Nejat
Brief Review on adding vectors
• If you do not remember how to add
vectors in component form, you
should watch the tutorial video on
vectors posted on ELM
• DO NOT SKIP THIS STEP OR YOU
WILL BE LOST FOR THE REST OF
THE TERM!
PHYS 1L03, Winter 2009, McMaster University, R.Nejat
Brief Review on adding vectors
• We can always
break any 2D
vector up into
components
along two
perpendicular
axes, such as x
and y:
θ
PHYS 1L03, Winter 2009, McMaster University, R.Nejat
θ
Brief Review on adding vectors
y
x
A
A
A
r
r
r
+
=
θ
cos
A
A
x
=
sin
A
A
y
=
2
2
2
x
x
A
A
A
+
=
2
2
x
x
A
A
A
+
=
x
y
A
A
=
tan
(
)
y
x
A
A
A
r
r
r
,
=
()
y
x
A
A
A
,
=
r
,
A
A
=
r
PHYS 1L03, Winter 2009, McMaster University, R.Nejat
Review: Adding two vectors:
• Find the resultant of two vectors F
1
and F
2
, shown below
∑
=
iy
y
F
R
F
1
F
2
R
∑
=
ix
x
F
R
2
1
F
F
R
r
r
r
+
=
A simple way to find the resultant of two
vectors is finding the components of it.
1. Find the x and y components of each
vector.
2. x-component of resultant is the
summation (algebraically) of x-
components of vectors.