unless acted upon by an unbalanced force.' As the long as the forces are not unbalanced - that is, as long as the forces are balanced - the first law of motion applies. The condition is described by the phrase '. There is an important condition that must be met in order for the first law to be applicable to any given motion. All objects resist changes in their state of motion - they tend to 'keep on doing what they're doing.' The state of motion of an object is maintained as long as the object is not acted upon by an unbalanced force. If in motion with a leftward velocity of 2 m/s, they will continue in this same state of motion (2 m/s, left). If in motion with an eastward velocity of 5 m/s, they will continue in this same state of motion (5 m/s, East).

If at rest, they will continue in this same state of rest. The behavior of all objects can be described by saying that objects tend to 'keep on doing what they're doing' ( unless acted upon by an unbalanced force). The two parts are summarized in the following diagram. There are two clauses or parts to this statement - one that predicts the behavior of stationary objects and the other that predicts the behavior of moving objects. Newton's first law of motion is often stated as An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. The focus of Lesson 1 is Newton's first law of motion - sometimes referred to as the law of inertia. These three laws have become known as Newton's three laws of motion. Isaac Newton (a 17th century scientist) put forth a variety of laws that explain why objects move (or don't move) as they do. In this unit (Newton's Laws of Motion), the ways in which motion can be explained will be discussed. The diagram shows an example of a situation where three forces sum to zero it illustrates a vehicle parked on a hill at rest and a vector triangle that shows the forces.Ī normal reaction force acts on all four wheels the arrow shown on the diagram represents the sum of these forces.In a previous chapter of study, the variety of ways by which motion can be described (words, graphs, diagrams, numbers, etc.) was discussed. You have already studied examples of a vehicle moving at constant velocity where the driving force and resistive force are equal in size and act in opposite directions. The closed figure is a triangle if there are three forces acting a quadrilateral for four forces, etc. If there are three or more forces acting then the vector diagram is a closed figure. This means that where there are two forces acting on an object that satisfies these conditions, they must be equal in size and opposite in direction. If an object is at rest or moving at constant velocity the resultant force on it is zero The converse of Newton’s first law is also true:

The nearest that we can get to modelling motion with no resistive forces is to study motion on ice or an air track.

Motion without resistive forces is difficult to achieve on Earth: there is always air resistance or friction from a surface that a moving object rests on. The phrase ‘uniform motion’ means moving in a straight line at constant speed i.e. Newton realised that in this case the unseen resistive forces of friction and air resistance together act in opposition to the motion as there is no longer a driving force after the object has been pushed, there is a resultant backwards-directed force acting on it. This is not ‘continuing in a state of uniform motion’. Give an object a push and it slows down before coming to rest. An object maintains its state of rest or uniform motion unless there is a resultant force acting on it.Īt first, this seems contrary to everyday experience.

What is newtons first law of motion