Force

Push or pull on an object is called force. Force is that cause which produces acceleration in the body on which it acts.


Types of Force

Resultant Force

If a single force acting on a body produces the same acceleration as produced by a number of forces, that single force is called the resultant of these individual forces. The resultant force is also called a net force.



Balanced & Unbalanced Force

If a set of forces acting on a body produces no acceleration in it the forces are said to be balanced. If it produces a non zero acceleration the poles are said to be unbalanced.

Galileo's Experiments


Laws of Motion

First Law of Motion


This law concludes that a body at rest will remain at rest and a body in motion will remain in uniform motion unless acted upon by an unbalanced force.



Second Law of Motion


This law concludes that the rate of change of momentum of an object is proportional to the net force applied on the object. The direction of the change of momentum is the same as the direction of the net force.



Third Law of Motion

This law concludes that in any interaction between two bodies, the force applied by the first body on the second is equal and opposite to the force applied by the second body on the first.




Conservation of Linear Momentum


According to Newton's first law, a particle remains at rest or moves with a constant velocity if the total force acting on it is zero. In this case, linear momentum which is mass times velocity also remains constant. This is an example of a very important law of physics called the principle of conservation of linear momentum.

Principle of Conservation of Linear Momentum

If the net external force on a system of particles is zero, the linear momentum of the system remains constant.

Pressure

Pressure is the physical quantity that relates the force acting on an object in the area on which it acts.

Thrust

Total force acting on a given surface is called Thrust.

Buoyancy

When a solid is partially or completely immersed in a fluid, the fluid exerts an upward force on the solid. This force is called the force of buoyancy, buoyant force or upthrust.

Force and Laws of Motion Notes - Physics - Class 9th