Explanation : Only energy transfer can takes place in closed system. When both the energy as well as the mass transfer take place in system then it is called open system. Only energy transfer can takes place in closed system. When both the energy and the mass transfer are restricted then the system is called isolated system. Thus we define work as being positive when the system does work on the surroundings energy leaves the system.
If work is done on the system energy added to the system , the work is negative. When a system has work done on it, the internal energy of the system increases. Work done is zero when the force is perpendicular to the displacement. It can also be zero if either the force or the displacement are zero. Work can be either positive or negative: if the force has a component in the same direction as the displacement of the object, the force is doing positive work. If the force has a component in the direction opposite to the displacement, the force does negative work.
Your hands apply a force on the bag to balance the force of gravity exerted on it but since there is no displacement of the bag, the work done on it by you your force and also the gravity is zero.
When force and displacement are in the same direction, the work performed on an object is said to be positive work. Example: When a body moves on the horizontal surface, force and displacement act in the forward path. The work is done in this case known as Positive work. Begin typing your search term above and press enter to search.
Press ESC to cancel. Skip to content Home Engineering How do Streaklines differ from streamlines? Ben Davis May 7, How do Streaklines differ from streamlines? If at a certain point in time all the particles introduced one after the other are joined together, a so-called streakline is formed.
A streakline is the connecting line of particles introduced one after another in thought into a flow! In the case of a unsteady streaming waters, one can imagine the streaklines as follows. For this purpose, imagine balls of plastic, which are connected to each other by an imaginary string. These balls are now brought into the water at the same position one after the other point A in the upper figure. The imaginary string then describes the streakline.
In the case of a steady flow, streaklines are in turn identical to pathlines and streamlines. The temporal behavior of a flow especially a turbulent flow can also be made visible with so-called timelines. A timeline can be used to visualize particles in a fluid, which are not introduced one after the other at the same place, but at different places at the same time.
The connecting line of these introduced particles determines the timeline at any further point in time. Home Mechanics Gases and liquids Chemistry Structure of matter Atomic models Chemical bonds Material science Structure of metals Ductility of metals Solidification of metals Alloys Steelmaking Iron-carbon phase diagram Heat treatment of steels Material testing Mechanical power transmission Basics Gear types Belt drive Planetary gear Involute gear Cycloidal gear Thermodynamics Temperature Kinetic theory of gases Heat Thermodynamic processes in closed systems Thermodynamic processes in open systems Optics Geometrical optics.
Sign in. Forgot your password? Get help. Privacy Policy. Password recovery. Home Mechanics Gases and liquids Difference between streamlines, pathlines, streaklines and timelines. Figure: Pathlines in a laminar and a turbulent flow. Why does water boil faster at high altitudes? Derivation of the Navier-Stokes equations. Derivation of the Euler equation of motion conservation of momentum. Derivation of the continuity equation conservation of mass. As can be seen in this chapter, the analysis results for transient flows will be different depending on the method used to visualize the flow.
Understanding this difference is important when visualizing analysis and experimental results. His doctoral research focused on numerical method for fluid-solid interaction problem. He is a consulting engineer at Software Cradle and provides technical support to Cradle customers. He is also an active lecturer at Cradle seminars and training courses.
Column: CFD basics. Such a bundle is called stream tube and is very useful in analysing flows. If one aligns a coordinate along the stream tube then the flow through it is one-dimensional. This is generated by injecting a dye into the fluid and following its path by photography or other means Fig. Streakline concentrates on fluid particles that have gone through a fixed station or point.
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