Newtonian Mechanics The velocity of a particle or a particle like body can change (the particle can accelerate) when the particle is acted on by one or more forces (pushes or pulls) from other objects. Newtonian mechanics relates accelerations and forces.

Force Forces are vector quantities. Their magnitudes are defined in terms of the acceleration they would give the standard kilogram. A force that accelerates that standard body by exactly is  defined to have a magnitude of I N. The direction of a force is the direction of the acceleration it causes. Forces are combined  cording to the rules of vector algebra. The net force on a body is the vector sum of all the forces acting on it.

A free body diagram is helpful in solving problems with the second law: It is a stripped-down diagram in which only one body is considered. That body is represented by a sketch or simply a . The external forces on the body are drawn. and a coordinate system is superimposed, oriented so as to simplify the solution.

Some Particular Forces A gravitational force on a body is a pull by another body. In most situations in this book, the other body is Earth or some other astronomical body. For Earth, the force is directed down toward the ground. which is assumed to be an Mass The mass of a body is the characteristic of that body that inertial frame. With that assumption, the magnitude of the force where is the body’s mass and g is the magnitude of the free fall acceleration.

Newton’s Third Law If a force  acts on body B due to body C, then there is a force  on body C due to body B. The forces are equal in magnitude and opposite in direction.


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