# Force

## Explanation

Force F (N) is the push or pull experienced when two masses interact with each other, either physically or at a distance. An object would either be at rest or in motion. The resistance to its state of motion or rest is called as inertia. Due to this property, an object will not experience any change in its state of motion or rest unless acted upon by an external force. When the object is in motion, the product of its mass m (kg) and acceleration a (m/s2) gives the vector sum of all the forces acting on it. When this object A interacts with another object B, then the object B would exert a force equal to the magnitude of the force exerted by the object A, but in the opposite direction.

### Newton's laws of motion

Sir Issac Newton used three laws to explain force and motion of various physical systems. These laws laid the foundation for the classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. They have been expressed in several different ways, over nearly three centuries, and can be summarized as follows.

1. When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity unless acted upon by a force.
2. The vector sum of the forces $\vec{F}$ on an object is equal to the mass $m$ of that object multiplied by the acceleration vector $\vec{a}$ of the object: ${\vec{F}=m\vec{a}}$.
3. When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.

### How does gravity work?

The presence of mass in the universe affects the geometry of space-time continuum. The effect of this alteration in the geometry is perceived as gravity.

### How weak force work?

A weak force or weak interaction works by the emission or absorption of elementary particles called as W and Z bosons, causing beta decay.

### What are inertial forces?

Inertial forces are the forces that resist any change in velocity. This means inertial forces are pseudo forces experienced by a body due to acceleration.

### What is an inertial frame of reference?

An inertial frame of reference is a reference system of coordinates that are used to measure any mechanical observation under constant motion or rest. A good example of an inertial frame of reference is an observer measuring the motion of a ball inside a train that is moving at a constant speed and a straight line. He measures it relative to the train's frame of reference, which is an inertial frame of reference. The inertial frame of reference is usually defined as the frame of reference where the laws of physics hold.

### What is a non-inertial frame of reference?

The non-inertial frame of reference is the reference frame where the velocity is not constant. In an accelerating frame, the pseudo forces will be experienced and the laws of motion don't hold. A good example for a non-inertial frame of reference is a rotating frame of reference where pseudo forces like centrifugal force and Coriolis force are experienced.

No.

### What is a conservative force?

A conservative force is a force that does work on an object displacing it between two points independent of the path taken by it. Gravitational force is a good example of a conservative force. When you lower an object from a certain height of A to a new height of B, the work done by gravity is the same even if you follow different paths to move the object from A to B.

### What makes the gravitational field?

Stress-energy tensor explains the curvature of the space-time, which can be used to explain about the particles that make gravitational field. A simple explanation is - anything with energy can contribute to the gravitational field.