السابعة المحاضرة
The Laws of Motion
The Laws of Motion
Chapter 5
5.1 The Concept of Force
The body is moving, When it change its position during a limited time.
5.1 The Concept of Force
Types of Motion:
5.1 The Concept of Force
. An object accelerates due to an external force.
.Force is a vector quantity
Definition of equilibrium
object is in equilibrium if: The net force acting on the object is
zero ,
. The object remains at rest.
.or continues to move with constant velocity.
Measuring the Strength of a Force
It is convenient to use the deformation of a spring to measure force.
Newton ‘s laws of motion
FIRST NEWTON’s LAW
SECOND NEWTON’s LAW
THIRD NEWTON’s LAW
5.2 Newton’s First Law
Newton’s first law (law of inertia):
“In the absence of external forces, an object at rest remains at rest and an object in motion continues in motion with a constant velocity (that is, with a constant
speed in a straight line)”.
5.3 Mass
. Mass (m) is that property of an object that specifies how much resistance an object exhibits to changes in its velocity.
. The SI unit of mass is the kilogram (Kg).
. mass is a scalar quantity
5.3 Mass
Mass and weight
The Weight of an object (W):
. W = the gravitational force exerted on the object
. W varies with locationThe Mass (m) :
. Is the same everywhere
5.4 Newton’s Second Law
“The acceleration of an object is directlyproportional to the net force acting on it and
inversely proportional to its mass.”
: is the net forcea : the acceleration.m: mass.
5.4 Newton’s Second Law
SI unit of force:
CGS unit of force:
2s
mKgNewton
2s
cmgDyne
5.4 Newton’s Second Law
5.4 Newton’s Second Law
Example 5.1
Question 2
Question 3
Problem 5.1
Problem 5.3
Problem 5.11
Problem 5.11
5.5 The Gravitational Force and Weight
Gravitational force Fg :The attractive force exerted by the Earth on an object.
.The magnitude of Fg:
.Direction: Toward the center of earth
5.5 The Gravitational Force and Weight
5.5 The Gravitational Force and Weight
5.5 The Gravitational Force and Weight
Problem 5.9
5.6 Newton’s Third Law
“ If two objects interact, the force F12 exerted by object 1 on object 2 is equal in magnitude and opposite in direction to the
force F21 exerted by object 2 on object 1:”
5.6 Newton’s Third Law
“The action force is equal in magnitude to the reaction force and opposite in
direction ”. The action and reaction forces:
. act on different objects.
. and must be of the
same type.
5.6 Newton’s Third Law
5.7 Some Applications of Newton’s Laws
.Tension Force
.Frictional Force: (in opposite of mosion direction)
.Elevator
.The Atwood Machine
.Inclined surface
Example 5.4 A Traffic Light at Rest
Example 5.4 A Traffic Light at Rest
Inclined Surface
One Block Pushes Another
Elevator
Example 5.8 Weighing a Fish in an Elevator
Example 5.8 Weighing a Fish in an Elevator
The Atwood Machine
Acceleration of Two Objects Connected by a Cord
Problem 21
Problem 21
Problem 23
Problem 24