1, without mass and volume: the definition of a particle requires that it has no mass and volume. This means that particles do not occupy real space and can be regarded as idealized points. Therefore, the position of particles is completely determined by their spatial coordinates.
2. Motion state: The particles are in motion state and can move along a straight line or curve. The position of a particle changes with time and can be described by a displacement vector. In kinematics, we study the trajectory, velocity and acceleration of particles.
3. Newton's second law applies: when a particle is acted by an external force, according to Newton's second law, it will produce acceleration. Newton's second law can be expressed as F=ma, where f is the resultant force acting on a particle, m is the mass of the particle and a is the acceleration of the particle.
4. Not affected by internal force: particles will remain static or move in a straight line at a constant speed without external force. When a particle is acted by an external force, it will change its motion state. But the particle is not affected by internal force, that is, the interaction force comes from the particle itself.
5. Simplify complex systems: Particle models are usually used to simplify the analysis of complex systems. By abstracting objects into particles, we can ignore their details and complexity, thus making it easier to carry out mathematical modeling and calculation.
Matters needing attention when treating an object as a particle
1. Ignore shape and size: The particle model assumes that the object has no shape and size, so it is necessary to ignore the shape and size of the object when using the particle model. This means that we only pay attention to the mass and position of the object, without considering its specific shape.
2. Define centroid: centroid is a very important concept in particle model. The center of mass is the geometric center of all mass distribution of an object, which can be regarded as the position of a particle. When calculating the motion of particles, in order to simplify the analysis of problems, force and acceleration are usually added to the center of mass.
3. Suitable for objects small enough: Particle model is more suitable for objects small enough, that is, its size can be ignored compared with other scales of the problem. For large objects or objects with obvious deformation, particle model may not accurately describe their motion.