Motion refers to a change in location. Physics is the scientific study of matter, energy, and the interactions between them. It includes fields such as acoustics, cryogenics, electromagnetism, optics, and mechanics, which refers to the study of how force act on matter or material systems and includes motion physics, the scientific study of movement.
In motion physics, it is typical to speak of the change in location of a “body.” Applied force is the initiator of a change in motion, which can mean starting motion, stopping motion, or changing direction. Without an applied force, bodies tend to resist acceleration and to stay at rest if they are at rest or, when moving in a straight line, to continue moving in a straight line.
Motion is usually described using several typical parameters, including velocity. Velocity is the rate of change in a body’s position, so it refers to both speed — distance covered in a certain amount of time — and direction, and so it is a vector. Despite this, it is often represented by the equation v = d/t, where v represents velocity, d represents distance, and t represents time. It is usually reported in meters per second.
The second parameter is acceleration, which is the change in velocity over time. Like velocity, acceleration is a vector. It is caused by a force applied to the body.
The greater the mass of the body, the more force must be applied to cause a certain amount of acceleration. This relationship is expressed by the equation F = ma where F represents force, m represents mass, and a represents acceleration. The directional aspect of the force is also important. Acting in the same direction as the original velocity of a body, force will only change speed and not direction. Acting in the opposite direction of the original velocity, the speed will be decreased, rather than increased.
Momentum is another term frequently used in motion physics and, like velocity, it is a vector. As defined in classical mechanics, momentum is the product of the velocity of an object and its mass. It is expressed by the equation p = mv where p represents momentum, m represents mass, and v represents velocity. The directionality of momentum is the same as the directionality of velocity, and the change in momentum when a force is applied is related to both the amount of force and the length of time for which it is applied.