Tiêu đề PHYSICS PART -2.pdf ✅

PHYSICS Class - C4(Part - II) INDEX INDEX S.No. Concept Topics Page No. 1. Wise Up 6 − 7 2. II Nowton's first law 07 − 11 3. III Newton's II law 11 − 13 4. IV Newton's III law 13 − 16 5. V Free body diagram 16 − 19 6. VI Apparent Weight 20 − 31
7. Additional Exercise 31 − 33 8. Quick Review 34 − 38 9. Analyse and Assess 39 − 43 5 NEWTON'S LAWS OF MOTION WISE UP 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. TYPES OF FORCES 1. Gravitational force : The force that acts between massive objects is known as gravita tional 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 known as nomal force. 3. Frictional force : The force that acts parallel to the contact surface between the objects is known as frictional force. 4. Tenstion : 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 NEWTON'S FIRST LAW : Every body continues to be in its state of rest or in uniform motion along a straight line unless it is acted only by an external force to change its state. Newton's first law of motion explains the concept of force qualitatively. If a net force acts on a particle it accelerates. LINEAR MOMENTUM : The linear momentum of a particle is the product of its mass and velocity. P⃗ = mV⃗ Linear momentum is a vector, it points in the direction of the velocity of the particle. NEWTON"S SECOND LAW : According to Newton II law of motion, the rate of change of linear momentum of a particle is equal to the net force on the particle. F = ma IMPULSE : Force acting for a short duration and which vary with time are impulsive forces. Ex : a) Force acting between the balls during collision between two billiard balls b) F orce exerted when nail driven into a wall by striking it with a hammer.
The impulse of a force is defined as the product of the average force and the time interval for which it acts. Impulse, J = FAV ⃗⃗⃗⃗⃗⃗ Δt = mv − mu⃗ NEWTON'S THIRD LAW : For every action there is always an equal and opposite reaction. Action and reaction are equal in magnitude and opposite in direction and they act on two different bodies (So they do not cancel). Newton's third law leads to law of conservation of linear momentum. A bird is in a wire cage hanging from a spring balance. When the bird starts flying in the cage, the reading of the balance decreases. In the above case, if the bird is in a closed cage or airtight cage and it hovers in the cage, the reading of the spring balance does not change. In the above case for a closed cage if the bird accelerates upward reading of the balance is R = Wbird + ma, where m is the mass of the bird and a is acceleration. VI. LAW OF CONSERVATION OF LINEAR MOMENTUM : • In the absence of an external force, the linear momentum of a particle or a body remains constant i.e., if F = 0 then p = constant • In the absence of external force, the linear momenta of individual particles can change but the total linear momentum of the whole system remains constant. • The law of conservation of linear momentum is based on the Newton's third law of motion. This is the fundamental law of nature and there is no exception to it.