المحاضرة السابعة 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:

. Force is a vector quantity 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).”

. The SI unit of mass is the kilogram (Kg). . 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

The Weight of an object (W): Mass and weight The Weight of an object (W): . W = the gravitational force exerted on the object . W varies with location The Mass (m): . Is the same everywhere

5.4 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”. :is the net force a : the acceleration. m: mass.

5.4 Newton’s Second Law SI unit of force: CGS unit of force:

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 Nora decided to live on the moon surface because her weight becomes list than her Wight on the surface of the earth? what is your opinion?

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”:

. act on different objects . . and must be of the 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