1. Newton's Laws of Motion 1. Newton 1 st law of motion 2. Newton 3 rd law of motion 3. Newton 2 nd law of motion

2. Newton 1 st law of motion Newton's first law of motion is often stated as: Newton's first law of motion is often stated as: An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction Unless acted upon by an unbalanced force

3. there are two parts to this statement: 1-prediction of the behavior of stationary object 2-prediction of the behavior of moving object The two parts are summarized in the following diagram

4. Balanced and Unbalanced Forces consider a physics book at rest on a table top. There are two forces acting upon the book. consider a physics book at rest on a table top. There are two forces acting upon the book.. One force - the Earth's gravitationalpull - exerts Force the other force the push of the table on the book (normal force) pushes upward on the book downward

5. Since the tow forces are of equal magnitude and in opposite Direction they balance each other the book is said to be in Equilibrium there is o unbalanced force act upon on the book And thus the book maintain its state of motion

6. For every action there is an equal and opposite reaction.. In other words, when one object exerts a force on another object, the second object exerts a force of equal strength in the opposite direction on the first object Newtons 2 nd law of motion

7. Consider the flying motion of birds. A bird flies by use of its wings. The wings of a bird push air downwards the air must also be pushing the bird upwards Action- reaction force pairs make it possible for birds to fly.

8. Newton 2 nd law of motion The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object. The acceleration of an object is directly proportional to the net force acting on the object, is in the direction of the net force, and is inversely proportional to the mass of the object. Example: what force is necessary to cause a 1000 kg car to accelerate at 2 m/s2? F=m a = 1000 kg x 2 m/s2 = 2000 kg-m/s2 = 2N F=m a = 1000 kg x 2 m/s2 = 2000 kg-m/s2 = 2N

9. From our daily life, we can can observe that: From our daily life, we can can observe that: 1. When a force F is applied on an object, V, the change of the velocity of the object, increases with the length of time delta t increases; 2. The greater the force F, the greater V; and 3. The larger the body (object) is, the less easily accelerated by forces.

10. Newton's second law The acceleration is directly proportional to the net force applied. The acceleration is directly proportional to the net force applied. The net force also determines the direction of the acceleration The direction of the acceleration is in the same direction as the net force. The acceleration is inversely proportional to the mass of the object.

11. Newtons second law state that: "If the net force on an object is not zero, the object will accelerate. The direction of the acceleration is the same as the direction of the net force. The magnitude of the acceleration is directly proportional to the net force applied, and inversely proportional to the mass of the object."

12. Free Body Diagrams Some examples will have more than one force acting on an object. It is advisable to draw a diagram of the situation showing the direction of all forces present acting through one point. These are known as free body diagrams. Some examples will have more than one force acting on an object. It is advisable to draw a diagram of the situation showing the direction of all forces present acting through one point. These are known as free body diagrams.

13. Examples A woman is standing on a set of bathroom scales in a stationary lift everyday.The reading on the scales is 500 N. When she presses the ground floor button, the lift accelerates downwards and the reading on the scales at this moment is 450 N. Find the acceleration of the lift

14. A ski tow pulls two skiers who are connected by a thin nylon rope along a frictionless surface. The tow uses a force of 70 N and the skiers have masses of 60 kg and 80 kg. Find A ski tow pulls two skiers who are connected by a thin nylon rope along a frictionless surface. The tow uses a force of 70 N and the skiers have masses of 60 kg and 80 kg. Find a) acceleration of the system b) tension in the rope. a) Total mass, m = 140 kg, a = F/m = 70/140 = 0.5 m s-2 b) Consider the 60 kg skier alone. Tension, T = ma = 60 x 0.5 = 30 N

15. Force Acting Down a Plane If an object is placed on a slope then its weight acts vertically downwards. A certain component of this force will act down the slope. The weight can be split into two components at right angles to each other. If an object is placed on a slope then its weight acts vertically downwards. A certain component of this force will act down the slope. The weight can be split into two components at right angles to each other.