1
00:00:01,470 --> 00:00:05,170
Last week, we discussed
the kinematics of motion.

2
00:00:05,170 --> 00:00:07,470
How one describes the
motion of an object

3
00:00:07,470 --> 00:00:11,500
by specifying its position,
velocity, and acceleration

4
00:00:11,500 --> 00:00:13,600
as a function of time.

5
00:00:13,600 --> 00:00:16,140
This week, we will
continue by discussing

6
00:00:16,140 --> 00:00:17,810
the dynamics of motion.

7
00:00:17,810 --> 00:00:20,540
How the application
of forces on an object

8
00:00:20,540 --> 00:00:24,170
changes the geometry or
trajectory of its motion.

9
00:00:24,170 --> 00:00:27,220
We will see that the applied
forces and the change

10
00:00:27,220 --> 00:00:30,050
in trajectory are related
through Newton's laws

11
00:00:30,050 --> 00:00:31,330
of motion.

12
00:00:31,330 --> 00:00:35,110
We will begin by reviewing
Newton's three laws of motion.

13
00:00:35,110 --> 00:00:36,970
These were a
landmark achievement

14
00:00:36,970 --> 00:00:38,820
in scientific thought.

15
00:00:38,820 --> 00:00:41,180
Most people who
haven't studied physics

16
00:00:41,180 --> 00:00:44,180
tend to intuitively think in
terms of the ancient mechanics

17
00:00:44,180 --> 00:00:48,460
of Aristotle in which an applied
force is required to maintain

18
00:00:48,460 --> 00:00:50,850
a body in uniform motion.

19
00:00:50,850 --> 00:00:52,850
Superficially,
this seems to agree

20
00:00:52,850 --> 00:00:54,960
with our everyday
experience, but only

21
00:00:54,960 --> 00:00:57,280
because friction plays
such an important role

22
00:00:57,280 --> 00:00:58,830
in our everyday life.

23
00:00:58,830 --> 00:01:01,520
One of Newton's
great insights was

24
00:01:01,520 --> 00:01:05,129
that applied forces cause
changes in an object's motion,

25
00:01:05,129 --> 00:01:09,170
rather than being necessary
to maintain uniform motion.

26
00:01:09,170 --> 00:01:11,260
Newton's laws were
the end result

27
00:01:11,260 --> 00:01:13,800
of a great deal of
careful definition,

28
00:01:13,800 --> 00:01:16,700
observation, and reasoning
by many scientists

29
00:01:16,700 --> 00:01:18,560
up to and including Newton.

30
00:01:18,560 --> 00:01:20,680
It is a fascinating
and compelling chapter

31
00:01:20,680 --> 00:01:22,940
in the history of science,
but we will not discuss

32
00:01:22,940 --> 00:01:24,750
that history in this course.

33
00:01:24,750 --> 00:01:28,150
Instead, we will simply state
Newton's three laws of motion

34
00:01:28,150 --> 00:01:31,720
as assumed postulates or axioms
and discuss their meaning

35
00:01:31,720 --> 00:01:33,479
and application.

36
00:01:33,479 --> 00:01:36,729
Finally, we will consider
several specific examples

37
00:01:36,729 --> 00:01:41,450
of physical forces, such as
gravity, contact forces exerted

38
00:01:41,450 --> 00:01:44,710
by a solid surface, like the
so-called normal force, which

39
00:01:44,710 --> 00:01:47,690
acts perpendicular or
normal to the surface,

40
00:01:47,690 --> 00:01:51,200
and friction, which acts
parallel to the surface,

41
00:01:51,200 --> 00:01:54,539
pulling forces like
tension in a rope or chain,

42
00:01:54,539 --> 00:01:57,560
and the force exerted by a
stretched or compressed spring

43
00:01:57,560 --> 00:01:59,979
described by Hooke's law.

44
00:01:59,979 --> 00:02:02,490
Taken as a whole,
this week will show us

45
00:02:02,490 --> 00:02:05,870
how to connect the two sides of
Newton's Second Law of Motion,

46
00:02:05,870 --> 00:02:08,919
f equals ma, the
dynamics or application

47
00:02:08,919 --> 00:02:11,550
of forces on the left-hand
side and its relation

48
00:02:11,550 --> 00:02:14,860
to the kinematics, the change in
geometry of the object's motion

49
00:02:14,860 --> 00:02:18,160
or trajectory, on
the right-hand side.