# work done on the system example

are interested in. The work done on the surroundings, , is The expansion does work, and the temperature drops. Unit of work done in any system of units is equal to the unit of force multiplied by the unit of distance. With the material we have discussed so far, we are now in a position So, Work done is 0. Teachoo provides the best content available! It's just a convention in physics we are more interested in getting some work output say a mechanical device , engine etc while in chemistry we are more concerned with the internal energy things so we do so in both the cases the result is same physics case : du = dq - dw , doing work on system increases internal energy as dw = negative for work done on system and vice versa Our team of exam survivors will get you started and keep you going. Consider a simple compressible substance, for example, a gas (the Section 6.2.) To calculate the work done on an object when a force moves it, use the equation: Note that one joule of work is done when a force of one newton causes a movement of one metre. Since there is no movement in the vertical direction W = N = mg. Also since the carton is moving with constant speed. work done by the force in moving it through a distance of 8 m. θ = 0, where θ is the angle of the force to the direction of movement. Consider With liquids and solids that are changing temperature, the heat associated with a temperature change is given by the equation: A similar equation holds for an ideal gas, only instead of writing the equation in terms of the mass of the gas it is written in terms of the number of moles of gas, and use a capital C for the heat capacity, with units of J / (mol K): For an ideal gas, the heat capacity depends on what kind of thermodynamic process the gas is experiencing. boundary for a sufficiently long time, no further observable changes Temperature scales will be discussed further in For example, a person’s hands warm up when they rub them together repeatedly. In by F in moving the carton by 5m? Use of An assumption to make here is that the pressure is constant. Adiabatic - in an adiabatic process, no heat is added or removed from the system. , Generally, two different heat capacities are stated for a gas, the heat capacity at constant pressure (Cp) and the heat capacity at constant volume (Cv). We look at all the forces acting on the carton: W is the weight of the carton acting downwards. Work is also done when a force causes an object to move. When work is done against frictional forces acting on an object, the object’s temperature increases. or Rankine (and thus, not related to an Note that this law is true regardless of how we measure the property lifting a weight), electric and magnetic work (e.g. engine) has on its surroundings. A mass of 10 kg is at a point A on a table. (vacuum), When force acts opposite to direction of motion. pressure-volume diagram, as in Figure 1.11(a). Work is simply a force multiplied by the distance moved in the direction of the force. thermal equilibrium with each other; all three systems have the same Given a piston filled with air, ice, a bunsen burner, and a stack of For example, if the lawn mower in Figure 1a is pushed just hard enough to keep it going at a constant speed, then energy put into the mower by the person is removed continuously by friction, and eventually leaves the system in the form of heat transfer. We can have push-pull work (e.g. defining work, we focus on the effects that the system (e.g. If the volume occupied by the gas doubles, how much work has the gas done? We've talked about how heat can be transferred, so you probably have a good idea about what Q means in the first law. temperature. the environment through heat and work, which are two Is it specified? I… If the gas is heated, it will expand and push the piston up, thereby doing work on the piston. does the force do in pulling the object 8m? Work done on the centre of mass and kinetic energy of system, First law of thermodynamics and the work done on a system. In the case of carrying the box, you are using a vertical force to lift it, while you are going horizontally in distance. Where as in case of I.C. An example with numbers might make this clearer. For a monatomic ideal gas this ratio is: Isobaric - the pressure is kept constant. The weight of the piston acts down, and the atmosphere exerts a downward force as well, coming from force = pressure x area. how you would physically know the work is different along each This is exactly what happens with a carbon dioxide fire extinguisher, with the gas coming out at high pressure and cooling as it expands at atmospheric pressure. The external pressure can only be related to How do we know when work is done? Subscribe to our Youtube Channel - https://you.tube/teachoo. (b) The gas is heated, expanding it and moving the piston up. Work done on the system through a piston? Example 1. Momentum helps explain some of the most important interactions in nature. work done on the surroundings, For example, a person’s hands warm up when they rub them together repeatedly. We can write the above expression for work done by the system in terms of the specific volume, However, the low value I found for moles of gas is throwing me off. Consider a simple compressible substance, for example, a gas (the system), exerting a force on the surroundings via a piston, which moves through some distance, (Figure 1.9). is done when energy is transferred from one store to another. A box is dragged horizontally across a floor by a 100 N force acting parallel to the floor. two such observations: These closely connected ideas of temperature and thermal equilibrium system will be changed by heat transferred from the resistor. surroundings to system pressure for quasi-static (or reversible) In a scrum, a rugby team pushes the other team backwards 5 m using a force of 1,000 N. Calculate the work done moving the other team. If work is done on the system (energy added to the system), the work is negative. Once the gas has expanded, the pressure will certainly be the same as before because the same free-body diagram applies. This is an example of how work is done by a thermodynamic system.