Force and Motion Sara Sultan 08/04/2019

Force Force can be described as a push or a pull. A force has both magnitude and direction, making it a vector quantity. It is measured in the SI unit of newton and represented by the symbol F. Force, in mechanics, is any action that tends to maintain or change the motion of a body or to stop it. Mechanics is a branch in which we study bodies under the influence of forces. Kinematics is a branch of mechanics which explains the motion only, without considering the cause of motion (force). Dynamics is a branch of mechanics which deals with the study of force and its types. 08/04/2019

Equations of motion 08/04/2019

Laws of motion Law of Inertia: Every object will remain at rest or in uniform motion in a straight line unless acted upon by an unbalanced external force. This is also called inertia. Law of acceleration: The second law explains how the velocity of an object changes when it is subjected to an external force. For an external applied force, the change in velocity (acceleration) depends on the mass of the object. Heavy mass, less acceleration, i.e. a = F/m An applied force will cause acceleration; F = ma Law of reaction: Every action has an equal and opposite reaction. If object A exerts a force on object B, then object B also exerts an equal force on object A. Fab = -Fba 08/04/2019

Linear Momentum Moving objects exerts force if they are stopped. Similarly, if two objects of different masses are travelling with same velocities, the heavier will exert more force. This feature of material objects was called quantity of motion by Newton and now it is called linear momentum and is defined by the relation P=mv Linear momentum is a vector quantity. SI unit: kgm/s or N.s. Dimension [MLT-1]. 08/04/2019

Impulse There are many situations in which the momentum of a body is suddenly changed such as collision of fast moving vehicles, striking a ball with a bat or hammering a nail into wood. The change in momentum is determined by a physical quantity known as impulse. For example, when a bat hits a cricket ball, the force certainly varies from instant to instant during the collision. In such cases, it is more convenient to deal with the product of force and time change in momentum instead of either quantity alone. The quantity (F × t)called impulse of force, where F can be regarded as the average force that acts during the time t. Mathematically, Impulse J = F×t = mvf_mvi = Δp and Force F = Δp/ Δt This equation means that the rate of change of momentum of the body is equal to the force acting on the body. 08/04/2019

Law of Conservation of Momentum An isolated system is a system that is free from the influence of a net external force that could change the momentum of the system. For a collision occurring between object 1 and object 2 in an isolated system, the total momentum of the two objects before the collision is equal to the total momentum of the two objects after the collision. That is, the momentum lost by object 1 is equal to the momentum gained by object 2. The above statement tells us that the total momentum of a collection of objects (a system) is conserved – i.e. a constant or unchanging value. 08/04/2019

Elastic & Inelastic Collusion An elastic collision is a collision in which there is no net loss in kinetic energy in the system as a result of the collision. Both momentum and kinetic energy are conserved quantities in elastic collisions. Only momentum is conserved in inelastic collisions. 08/04/2019

Projectile Motion It is motion in two dimensions. Main characteristics are: Horizontal component remains constant throughout the flight. Vertical component changes uniformly and is zero at highest point. Range of projectile is equal to maximum height at 76°. For complimentary pair of angles, the range is same. (80°, 10°), (70°, 20°), (60°, 30°) Maximum range is equal to 4 times corresponding height. R = 4H 08/04/2019