# force and laws of motion

Information about force and laws of motion

Published on August 6, 2014

Author: ashish8910

Source: authorstream.com

FORCE AND LAWS OF MOTION: FORCE AND LAWS OF MOTION ASHISH KUMAR IX A 05 Syllabus: Syllabus FORCE BALANCED FORCE AND UNBALANCED FORCE INERTIA LAWS OF MOTION LINEAR MOMENTUM IMPULSE CONSERVATION OF MOMENTUM FORCE: FORCE When we look around, and observe state of rest or motion of bodies, we find that nothing moves on its own. When we push or pull a body a) it may change its state of motion or of uniform motion b) it may change its direction of motion c) it may change its shape Force: Force Force is an entity which when applied on a body changes or tends to change a body’s i) state of rest or uniform motion ii) direction of motion iii) shape iv) speed A force has a magnitude and it is a vector quantity Force: Force TYPES OF FORCE: TYPES OF FORCE Balanced force – When a number of forces acting simultaneously on a body do not bring about any change in its state of rest or of uniform motion, then the force on the body are said to be balanced forces. Balanced forces do not produce any acceleration. Balanced force: Balanced force TYPES OF FORCE: TYPES OF FORCE Unbalanced force - When a number of forces acting simultaneously on a body bring change in its state of rest or of uniform motion, then the force on the body are said to be unbalanced forces. unbalanced forces produce acceleration, change direction of motion. Unbalanced force: Unbalanced force INERTIA: INERTIA Inertia is the tendency of a body to maintain its state of rest or of uniform motion on its own. Types of inertia a) Inertia of rest – It is the inability of a body by the virtue of which it cannot move by itself. A body remains at rest and can't start moving on its own due to inertia of rest b) inertia of motion - It is the inability of a body in motion to stop by itself. A body in uniform motion can neither accelerates nor retard on its own. EXAMPLES OF INERTIA OF REST: EXAMPLES OF INERTIA OF REST A passenger tends to fall backward, when the bus starts suddenly. As the feet touch the bus so, lower part of the body comes in motion while the upper part of the body stays at rest due to inertia of rest. Hence, he feels backward jerk. When we shake the branch of a fruit tree, branch comes in motion. But fruits remains at rest due to inertia of rest and falls down. Inertia of rest: Inertia of rest The coin and the card is at rest. The card comes in motion but the coin remains at rest. EXAMPLES OF INERTIA OF MOTION: EXAMPLES OF INERTIA OF MOTION a) A person trying to get down from a running bus falls forward .When the person gets down from a running bus the upper part of his body is still in motion and due to this inertia of motion the body topples forward even though he has set his foot on the ground. b) A toy thrown up by a boy inside a moving train moves along with the train. The toy also attains the same velocity as the train inside the train and thus would move along with the train when thrown up. This will apply only when the train is moving with a constant speed or it might fall forward or backward if the speed is altered. Laws of motion: Laws of motion a) First law of motion An object that is at rest will stay at rest unless an external force acts upon it. An object that is in motion will not change its velocity unless an external force acts upon it. This is known as  uniform motion . An object  continues  to do whatever it happens to be doing unless a force is exerted upon it. If it is at rest, it continues in a state of rest. If an object is moving, it continues to move without turning or changing its speed. Laws of motion: Laws of motion b) second law of motion Momentum (p) → Amount of motion possessed by a body is called it’s momentum. Numerically, it is product of mass of object and its velocity. P = mv It is a vector quantity and SI unit is kgm/s Laws of motion: Laws of motion b) second law of motion cont. Second law of states that the rate of change of momentum of an object is directly proportional to the applied unbalanced force in the direction of force. initial momentum = P 1 at t = 0 final momentum = P 2 at t = t sec. Change in momentum = P 2 – P 1 rate of change of momentum = P 2 – P 1 = P2 – P1 t - 0 t Laws of motion: Laws of motion c) third law of motion Each action there is an equal and opposite reaction. Provided that both forces are act on different object. Newton's third law of motion: Newton's third law of motion Impulse: Impulse  impulse is the product of a force, F, and the time, t, for which it acts. The impulse of a force acting for a given time interval is equal to the change in linear momentum produced over that interval. Impulse is a vector quantity since it is the result of integrating force, a vector quantity, over time. The SI unit of impulse is the Newton second or, in base units, the kilogram meter per second (kg·m/s). Impulse = F average Δ t = m Δ v CONSERVATION OF MOMENTUM : CONSERVATION OF MOMENTUM In a closed system the total momentum is constant. This fact, known as the  law of conservation of momentum , is implied by Newton's laws of motion. Suppose, for example, that two particles interact. Because of the third law, the forces between them are equal and opposite. CONSERVATION OF MOMENTUM: CONSERVATION OF MOMENTUM The conservation of momentum states: Momentum before  = Momentum after So, (P 1  + P 2 ) before= (P 1  + P 2 ) after Or, m 1 u 1  + m 2 u 2  = m 1 v 1  + m 2 v 2 Conservation of momentum PowerPoint Presentation: THE END