Chapter 5Newton’s laws of motion

Dr. Haykel Abdelhamid Elabidi

1st week of November 2013/DhH/Muh 1434

Units of Chapter 5

• Force and mass

• Newton’s first law of motion

• Newton’s second law of motion

• Newton’s third law of motion

• Contact force

Force and mass

• A force is a push or a pull.

• The force is a vector (defined by its magnitude and its direction).

• The mass of an object is a measure of how difficult it is to change its velocity: It is more difficult to stop a car than to stop a baseball.

• The mass can also be defined as the measure of the quantity of matter in an object.

Newton’s first law of motion

• An object at rest reamains at rest as long as no net force acts on it

• An object moving with constant velocity continues to move with the same velocity (same speed and direction) as long as no net force acts on it.

• In order to change the velocity of an object –magnitude or direction – a net force is required.

If the net force on an object is zero, its velocity is constant.

Newton’s second law of motion

• Acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass.

• Acceleration is inversely proportional to mass• Acceleration is proportional to force

These observation give: or

If an object have several forces acting on it; the acceleration is due to the net force (sum of force vectors):

The force is a vector, we can find its components:

Newton’s second law of motion

Exercise 5-1 p116:

Newton’s third law of motion

when two bodies interact, the force which body "A“ exerts on body "B" (the action force ) is equal in magnitude and opposite in direction to the force which body "B" exerts on body "A" (the reaction force). (the law of action-reaction)

Weight and normal force

Newton’s laws of motionExample 5-1 p119:

Example 5-2 p121:

Newton’s laws of motion

1 mi =1609 m

Newton’s laws of motionExample 5-3 p123:

Contact force

Thank you for your attention

See you next time Inchallah