Search results
Results From The WOW.Com Content Network
Therefore, = = = =, where Δp is the change in linear momentum from time t 1 to t 2. This is often called the impulse-momentum theorem (analogous to the work-energy theorem ). As a result, an impulse may also be regarded as the change in momentum of an object to which a resultant force is applied.
Then the angular equation in the momentum equations and the continuity equation are identically satisfied. The radial momentum equation reduces to ∂p / ∂r = 0, i.e., the pressure p is a function of the axial coordinate x only. For brevity, use u instead of . The axial momentum equation reduces to
Momentum depends on the frame of reference, but in any inertial frame of reference, it is a conserved quantity, meaning that if a closed system is not affected by external forces, its total momentum does not change. Momentum is also conserved in special relativity (with a modified formula) and, in a modified form, in electrodynamics, quantum ...
The way of obtaining a velocity field satisfying the above, is to compute a pressure which when substituted into the momentum equation leads to the desired correction of a preliminary computed intermediate velocity. Applying the divergence operator to the compressible momentum equation yields
It describes the rate of change of vorticity of the moving fluid particle. This change can be attributed to unsteadiness in the flow ( ∂ω / ∂t , the unsteady term) or due to the motion of the fluid particle as it moves from one point to another ((u ∙ ∇)ω, the convection term).
On the other hand, the pressure in thermodynamics is the opposite of the partial derivative of the specific internal energy with respect to the specific volume: (,) = (,) since the internal energy in thermodynamics is a function of the two variables aforementioned, the pressure gradient contained into the momentum equation should be explicited ...
In the above integral formulation of this equation, the term on the left is the net change of momentum within the volume. The first term on the right is the net rate at which momentum is convected into the volume. The second term on the right is the force due to pressure on the volume's surfaces.
The effect of the pressure gradient on the flow is to accelerate the flow in the direction from high pressure to low pressure. As written in the Cauchy momentum equation, the stress terms p and τ are yet unknown, so this equation alone cannot be used to solve problems.