Tiêu đề PHYSICS PART- 2.pdf ✅

PHYSICS Class - C3 (Part - II) NEWTON'S LAWS OF MOTION TISET:WISEUP FORCE : 'Force' generally denotes a push or a pull. A force may be defined as an external cause which changes or tends to change the state of rest or uniform motion of body in a straight line. Hence force is the cause of motion. EFFECTS OF FORCE : A force can bring about following effects as illustrated by the examples below:
1. To set a stationary body into motion. Ex: A horse can make a carriage move by applying the force in the forward direction. 2. To stop the moving bodies. Ex: A speeding car is stopped by the force of friction of brakes. 3. To change the speed or direction of a moving body. Ex: A stone projected vertically upward changes its speed as well as direction because of the force due to gravity. 4. To bring about change in dimensions. Ex: Length of a rubber band increases, when a stretching force is applied. TYPES OF FORCES : 1. Gravitational force : The force that acts between massive objects is known as gravitational force. Note: The force exerted by earth on objects present on earth is treated as weight of the object. 2. Normal force: The force that acts perpendicular to the contact surface between the objects is knowl as nomal force. 3. Frictional Force: The force that acts parallel to the contact surface between the objects is known a frictional force. 4. Tension: The force exerted by the string on the object connected to it is known as tension. 5. Spring Force: The force exerted by the spring is known as spring force.
UNITS OF FORCE : SI unit of force is newton (N) CGS unit of force is dyne gravitational units of force are kgf or kgwt. and gf or gwt. 1 N = 105 dyne 1dyne = 10−5 N 1kgf = 1kgwt = 9.8 N 1gf = 1gwt = 980 dyne Mass : The quantity of matter present in an object is known as mass. Units of mass : In SI - kg ; CGS - g Velocity : The rate of displacement is known as velocity. Units of velocity : In SI - m/s ; CGS - cm/s CONCEPT - INEWTON'S FIRST LAW Newton has given three laws to describe motion of an object. Newton's 1 " law: "If the vector sum of all the forces acting on a particle is zero then and only then the particle remains un accelerated" Newton 1 st law defines "force" and "Inertia". Force : "Force is a push or pull which changes (or) tends to change the state of rest (or) of uniform motion". Inertia : Inertia is the inherent property of a body to oppose change of motion. It can be expressed as the tendency of a body to oppose any change in its state of rest or uniform motion. The mass of a body is a measure of its intertia. Inertia is of three types :
i) Intertia of rest ii) Inertia of motion iii) Inertia of direction i) Inertia of rest : The inertia (resistance) offered by a body to change its state of rest is called inertia of rest. Ex 1. Passengers in a bus jerk in the backward direction when the bus suddenly starts. Ex 2. When a blanket is given a sudden jerk, the dust particles fall off. Ex 3. When you hit a striker on a pile of carrom counters, you will observe that only the lowest counter moves away. Ex 4. When a bullet is fired into a tightly - fitted glass pane from a reasonably close range, it makes a clear circular hole in the glass pane. ii) Inertia of motion : The inertia (Resistance) offered by a body to change its state of uniform motion is called inertia of motion. Ex 1. Passengers in a bus jerk in the forward direction when the bus suddenly comes to rest. Ex 2. When we switch off a fan it continues to rotate for a while due to inertia of motion. Ex 3. A person jumping from a moving bus in the direction of motion of the bus falls forward. Ex 4. An athlete runs for some distance before taking a long jump. In this way, the athlete gains momentum due to inertia of motion. iii) Inertia of direction : The resistance offered by a body to change its direction of motion is called inertia of direction. Ex 1. When a stone tied to one end of a string is whirled and the string breaks suddenly, the stone flies off along the tangent to the circle. Ex 2. When a car goes round a curve suddenly, the person sitting inside is thrown outwards.