3. The Laws of Motion: made 4 learnering

Motion

1. PHYSICS FOR ENGINEERS
LAWS OF MOTION

2. PHYSICS FOR ENGINEERS
FORCES
—A simple push or pull, therefore, it is a
vector quantity.
Has a unit of newton, N
D
E
M
P
C

3. PHYSICS FOR ENGINEERS
TYPES OF FORCES
Contact Forces — there
should be a direct contact
so see the effect of the
applied forces
Field Forces — the effect
of the force is felt even in
the absence of contact
(long range)
D
E
M
P
C

4. PHYSICS FOR ENGINEERS
TYPES OF FORCES
D
E
M
P
C
Gravity Force, Fg
—The force of gravity is the force with which the earth, moon, or other
massively large object attracts another object towards itself. By definition, this
is the weight of the object. All objects upon earth experience a force of gravity
that is directed "downward" towards the center of the earth. The force of
gravity on earth is always equal to the weight of the object as found by the
equation

5. Normal Force, Fn
—The normal force is the support force exerted upon an
object that is in contact with another stable object. For
example, if a television is resting upon a surface, then the
surface is exerting an upward force upon the television in
order to support the weight of the television . On occasions,
a normal force is exerted horizontally between two objects
that are in contact with each other.
PHYSICS FOR ENGINEERS
TYPES OF FORCES
D
E
M
P
C

6. PHYSICS FOR ENGINEERS
Friction Force, Ff
—The friction force is the force exerted by a surface as an object
moves across it or makes an effort to move across it.
Static Friction — friction that must be exceeded in order to start a
motion.
Kinetic Friction — friction existing between two moving bodies.
Ff = µ•F n
TYPES OF FORCES
D
E
M
P
C

7. PHYSICS FOR ENGINEERS
Tension force, Ft
The tension force is the force that is
transmitted through a string, rope, cable or wire
when it is pulled tight by forces acting from
opposite ends. The tension force is directed
along the length of the wire and pulls equally on
the objects on the opposite ends of the wire.
TYPES OF FORCES
D
E
M
P
C

8. (Law of Inertia)
PHYSICS FOR ENGINEERS
NEWTON’S FIRST LAW
An object moves with a velocity that is
constant in magnitude and direction,
unless acted on by a nonzero net force.
D
E
M
P
C

9. INERTIA AND MASS
Inertia — the tendency of the body to
continue in its original state of motion
Mass — measure of the objects resistance
of changes in its motion due to a force
PHYSICS FOR ENGINEERS
D
E
M
P
C

10. (Law of Acceleration)
PHYSICS FOR ENGINEERS
NEWTON’S SECOND
LAW
The acceleration of an object is directly
proportional to the net force acting on it
and inversely proportional to its mass.
D
E
M
P
C

11. (Law of Action-Reaction)
PHYSICS FOR ENGINEERS
NEWTON’S THIRD LAW
If object 1 and object 2 interact, the force
F12 exerted by object 1 on object 2
is equal in magnitude but opposite in direction
to the force F21 exerted by object 2 on
object 1.
D
E
M
P
C

12. PHYSICS FOR ENGINEERS
FREE BODY DIAGRAM
—Illustrations
of all forces
acting and or
applied to a
body.
D
E
M
P
C

13. PHYSICS FOR ENGINEERS
OBJECTS IN
EQUILIBRIUM
D
E
M
P
C

14. PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
Example 01
A traffic light weighing 100N
hangs from a vertical cable tied
to two other cables that are
fastened to a support. The
upper cables make angles of
37.0
O and 53.0
O with the
horizontal. Find the tension in
each of the three cables.

15. PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
Example 01

16. Example 02
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
A 10kg mass was suspended through a rope.
Find the tension in the rope

17. The combined weight of the crate and dolly is
300N. If the man pulls on the rope with a
constant force of 20.0 N, what is the acceleration
of the system (crate plus dolly), and how far will
it move in 2.00 s? Assume that the system starts
from rest and that there are no friction forces
opposing the motion.
Example 03
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

18. Example 03 solution
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

19. Example 04
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
Find the acceleration of the 20kg block when pulled by 50N
with direction 15 degrees above horizontal if...
a) the surface is frictionless
b) considering static Coefficient friction, µs=0.2 and the
kinetic coefficient friction, µk=0.1
is the force enough to cause motion to the block? If so,
find the acceleration.

20. Example 04 solution
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

21. Example 04 solution
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

22. let m1= 3kg, m2 = 12 kg
µk=0.1 ; µs=0.2
Find the acceleration of m1 when...
a)The system is frictionless
b)The system is with friction
Example 05
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

23. a) Free body diagram (frictionless)
Example 05 solution
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

24. b) Free body diagram (with friction)
Example 05 solution
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

25. b) Free body diagram (with friction)
Example 05 solution
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C

26. Example 06
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
Find the acceleration of 12kg block when...
a)The system is frictionless
b)The system is with friction
µk=0.1, µs=0.2

27. Example 06
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
a) Free body diagram (frictionless)

28. Example 06
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
a) Free body diagram

29. Example 06
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
b) Free body diagram (with friction)

30. Example 06
PHYSICS FOR ENGINEERS
APPLICATION
D
E
M
P
C
b) Free body diagram