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F is the resultant force applied, t 1 and t 2 are times when the impulse begins and ends, respectively, m is the mass of the object, v 2 is the final velocity of the object at the end of the time interval, and; v 1 is the initial velocity of the object when the time interval begins. Impulse has the same units and dimensions (MLT −1) as momentum.
A body remains at rest, or in motion at a constant speed in a straight line, except insofar as it is acted upon by a force. At any instant of time, the net force on a body is equal to the body's acceleration multiplied by its mass or, equivalently, the rate at which the body's momentum is changing with time.
Per unit volume, the rate of change in momentum is equal to ρ Dv / Dt . This is equal to the net force on the droplet. Forces that can change the momentum of a droplet include the gradient of the pressure and gravity, as above. In addition, surface forces can deform the droplet.
The moment of force, or torque, is a first moment: =, or, more generally, .; Similarly, angular momentum is the 1st moment of momentum: =.Momentum itself is not a moment.; The electric dipole moment is also a 1st moment: = for two opposite point charges or () for a distributed charge with charge density ().
Force is equal to the change in momentum per change in time (). For a constant mass, force equals mass times acceleration ( F → = m a → {\displaystyle {\vec {F}}=m{\vec {a}}} ). For every action, there is an equal and opposite reaction.
For example, if a person places a force of 10 N at the terminal end of a wrench that is 0.5 m long (or a force of 10 N acting 0.5 m from the twist point of a wrench of any length), the torque will be 5 N⋅m – assuming that the person moves the wrench by applying force in the plane of movement and perpendicular to the wrench.
Action has the dimensions of × , and its SI unit is joule-second, which is identical to the unit of angular momentum. Several different definitions of "the action" are in common use in physics. [11] [12] The action is usually an integral over time.
It is dimensionally equivalent to the momentum unit kilogram-metre per second (kg⋅m/s). One newton-second corresponds to a one-newton force applied for one second. = It can be used to identify the resultant velocity of a mass if a force accelerates the mass for a specific time interval.