Force is the physical quantity operating on a body which, in particular, tells him some acceleration. To find force impulse, it is necessary to define change of number of the movement, i.e. an impulse of the body.
Instruction
1. The movement of a material point is caused by influence of some force or forces which give it acceleration. The corresponding number of the movement is result of application of force of a certain size for some time. An impulse of force is called the measure of its action for a certain period: Ps = Fcp • ∆t, gdefsr – the average force operating on a body; ∆t is a time interval.
2. The number of the movement represents a body impulse. It is vector size, sonapravlenny speeds and equal to her work on body weight: Rt = m•v.
3. Thus, the impulse of force is equal to change of an impulse of a body: Pc = rt = m • (v-v0), gdev0 – initial speed; v – final speed of a body.
4. The received equality displays the second law of Newton in relation to an inertial reference system: the derivative of function of a material point on time is equal to size the constant force operating on it: Fcp • ∆t = rt → Fcp = dpt/dt.
5. The total impulse of a system of several bodies can change only under the influence of external forces, and its value in direct ratio to their sum. This statement is a consequence of the second and third laws of Newton. Let the system consist of three interacting bodies, then is true: Ps1 + Pc2 + Pc3 = rt1 + rt2 + rt3, gdepci – an impulse of force operating on i body; Pti is i body impulse.
6. This equality shows that if the sum of external forces zero, then the general impulse of the closed system of bodies is always constant in spite of the fact that internal forces change their impulses. This principle carries the name of law of conservation of momentum. At the same time it is necessary to consider that it is about the vector sum.
7. In reality the system of bodies seldom are closed as it is always affected at least by gravity. It changes a system impulse down, however does not influence it if the movement happens across.