What is Newton's first law ?

This postulate is known as the law of inertia. The law of inertia was first formulated by Galileo Galilei for horizontal motion on Earth and was later generalized by René Descartes.

Galileo it had been thought that all horizontal motion required a direct cause, but Galileo deduced from his experiments that a body in motion would remain in motion unless a force (such as friction) caused it to come to rest.

There was this fellow in England named Sir Isaac Newton. A little bit stuffy, bad hair, but quite an intelligent guy. He worked on developing calculus and physics at the same time.

During his work, he came up with the three basic ideas that are applied to the physics of most motion (NOT modern physics). The ideas have been tested and verified so many times over the years, that scientists now call them Newton's Three Laws of Motion.

The first law says that an object at rest tends to stay at rest, and an object in motion tends to stay in motion, with the same direction and speed. Motion (or lack of motion) cannot change without an unbalanced force acting

If nothing is happening to you, and nothing does happen, you will never go anywhere. If you're going in a specific direction, unless something happens to you, you will always go in that direction. Forever.

Have you ever noticed that their tools float? They can just place them in space and they stay in one place. There is no interfering force to cause this situation to change. The same is true when they throw objects for the camera. Those objects move in a straight line.

Newton's first law: An object at rest remains at rest, or if in motion, remains in motion at a constant velocity unless acted on by a net external force.

A force is a push or a pull exerted on one object by another object. The units of force FF are called Newtons or simply \text{N}N.

An external force is a force originating from outside an object rather than a force internal to an object. For instance, the force of gravity that Earth exerts on the moon is an external force on the moon.

The net force, written as \Sigma FΣF, on an object is the total force on an object. If many forces act on an object, then the net force is the sum of all the forces. But be careful—since force FF is a vector, to find the net force \Sigma FΣF, the forces must be added up like vectors using vector addition.

Newton's first law says that if the net force on an object is zero (\Sigma F=0ΣF=0), then that object will have zero acceleration. That doesn't necessarily mean the object is at rest, but it means that the velocity is constant. In other words, constant zero velocity—at rest—or constant non-zero velocity—moving with a constant velocity.

The property of a body to remain at rest or to remain in motion with constant velocity is called inertia. Newton’s first law is often called the law of inertia.

The property of a body to remain at rest or to remain in motion with constant velocity is called inertia. Newton’s first law is often called the law of inertia.

The inertia of an object is measured by its mass. Mass can be determined by measuring how difficult an object is to accelerate. The more mass an object has, the harder it is to accelerate.

A space probe is drifting to the right at a constant velocity in deep interstellar space—far from any influence due to planets and stars—with its rockets off.

If two rocket thrusters both turn on simultaneously exerting identical forces leftward and rightward in the directions shown, what would happen to the motion of the rocket?

The space probe would continue with constant velocity.

The space probe would speed up. c. The space probe would slow down and eventually stop.

The space probe would immediately stop.