Motion
When discussing Newton’s contribution to the science of motion, it is almost impossible to omit his Three Law of Motion. These three laws, outlined in Book I of the Principia, provide the basis for understanding motion in a day to day context.
“Every body continues in its state of rest, or uniform motion in a straight line, unless it is compelled to change that state by forces impressed on it.” This law, also known as the Law of Inertia, demonstrates that unless an unbalanced, or net, force (a force that does not have an opposing force balancing it out) acts on an object, that object’s velocity, or speed in a given direction, will not change. If the object is stationary, it will remain stationary and if it is moving it will continue to move at the same speed and in the same direction. For example, if an object is released into deep space, its velocity will not change. It won’t move in a particular direction; it will simply continue to move at a constant speed, in a constant direction. This is due to the fact that no forces are acting on it, meaning that no unbalanced forces are causing it to change its velocity.
“The change in motion is proportional to the motive force impressed and is made in the direction of the straight line in which that force is impressed (F=ma).” Put simply, if the forces on an object are unbalanced, that object will accelerate (or decelerate, if the acceleration value is negative) in the direction of the unbalanced force. The mass of the object, multiplied by its acceleration will show the amount of force required to overcome the opposite forces, causing the mass to accelerate the amount that it does. For example, if you push a book weighing 2kg across the table so that it accelerates to 1m/s², the unbalanced force of 2 N (newton) force has been applied to it, and the book will accelerate in the same direction as the force, or away from you. Similarly, the unbalanced force of friction causes the book to again change speed, thus changing its velocity, causing it to accelerate in the opposite, or negative direction; otherwise known as deceleration.
- Newton’s 1st Law of Motion:
“Every body continues in its state of rest, or uniform motion in a straight line, unless it is compelled to change that state by forces impressed on it.” This law, also known as the Law of Inertia, demonstrates that unless an unbalanced, or net, force (a force that does not have an opposing force balancing it out) acts on an object, that object’s velocity, or speed in a given direction, will not change. If the object is stationary, it will remain stationary and if it is moving it will continue to move at the same speed and in the same direction. For example, if an object is released into deep space, its velocity will not change. It won’t move in a particular direction; it will simply continue to move at a constant speed, in a constant direction. This is due to the fact that no forces are acting on it, meaning that no unbalanced forces are causing it to change its velocity.
- Newton’s 2nd Law of Motion:
“The change in motion is proportional to the motive force impressed and is made in the direction of the straight line in which that force is impressed (F=ma).” Put simply, if the forces on an object are unbalanced, that object will accelerate (or decelerate, if the acceleration value is negative) in the direction of the unbalanced force. The mass of the object, multiplied by its acceleration will show the amount of force required to overcome the opposite forces, causing the mass to accelerate the amount that it does. For example, if you push a book weighing 2kg across the table so that it accelerates to 1m/s², the unbalanced force of 2 N (newton) force has been applied to it, and the book will accelerate in the same direction as the force, or away from you. Similarly, the unbalanced force of friction causes the book to again change speed, thus changing its velocity, causing it to accelerate in the opposite, or negative direction; otherwise known as deceleration.
“To every action there is always an opposed and equal reaction.” In other words, if object A exerts a force on object B, then object B exerts an equal but opposite force on object A. This equal and opposite force is called the reaction force. If you push against a boulder with a certain amount of force, that boulder pushes back against you with an equal force. This reinforces the 1st and 2nd Laws of Motion, because unless the action force is greater than the reaction force, the object will not change its velocity. Unless you apply enough force to that boulder so that it is somehow greater than the force of friction, only then will the boulder move. |
Author: Hannah Davies