work

Examples of work in the following topics:

• Negative Work and Total Work

• Work

  • Thermodynamic work encompasses mechanical work (gas expansion, ) plus many other types of work, such as electrical.
  • As such, thermodynamic work is a generalization of the concept of mechanical work in mechanics.
  • Nevertheless, heat and work can produce identical results.
  • Both heat and work can cause a temperature increase.
  • Since pressure is constant, the work done is PΔV.

• Kinetic Energy and Work-Energy Theorem

  • The work-energy theorem states that the work done by all forces acting on a particle equals the change in the particle's kinetic energy.
  • The principle of work and kinetic energy (also known as the work-energy theorem) states that the work done by the sum of all forces acting on a particle equals the change in the kinetic energy of the particle.
  • A force does work on the block.
  • The kinetic energy of the block increases as a result by the amount of work.
  • This relationship is generalized in the work-energy theorem.

• Introduction to Work and Energy

  • Work is the energy associated with the action of a force.
  • An example of work is a pitcher throwing a ball.
  • Take this example of work in action from : (A) The work done by the force F on this lawn mower is Fdcosθ.
  • Work is closely related to energy.
  • Work is the energy associated with the action of a force.

• Conservation of Energy in Rotational Motion

  • Clearly, the motor had to work to get the stone spinning.
  • Work and energy in rotational motion are completely analogous to work and energy in translational motion and completely transferrable.
  • The final rotational kinetic energy equals the work done by the torque:
  • This confirms that the work done went into rotational kinetic energy.
  • To return to the grindstone example, work was done to give the grindstone rotational energy, and work is done by friction so that it loses kinetic energy.

• Work Done by a Variable Force

  • Integration is used to calculate the work done by a variable force.
  • Thus, a force does work when it results in movement.
  • For example, let's consider work done by a spring.
  • The SI unit of work is the joule (J), which is defined as the work done by a force of one newton moving an object through a distance of one meter.
  • Describe approaches used to calculate work done by a variable force

• The First Law

  • The 1st law of thermodynamics states that internal energy change of a system equals net heat transfer minus net work done by the system.
  • Heat engines are a good example of this—heat transfer into them takes place so that they can do work.
  • W is the total work done on and by the system.
  • W is positive when more work is done by the system than on it.
  • Explain how the net heat transferred and net work done in a system relate to the first law of thermodynamics

• Problem Solving with Dissipative Forces

  • In the presence of dissipative forces, total mechanical energy changes by exactly the amount of work done by nonconservative forces (Wc).
  • Since the work done by nonconservative (or dissipative) forces will irreversibly alter the energy of the system, the total mechanical energy (KE + PE) changes by exactly the amount of work done by nonconservative forces (Wc).
  • In terms of the work-energy theorem, the work done by friction (f), which is negative, is added to the initial kinetic energy to reduce it to zero.
  • The work done by friction is negative, because f is in the opposite direction of the motion (that is, θ=180º, and so cosθ=−1).
  • The most important point of this example is that the amount of nonconservative work equals the change in mechanical energy.

• Humans: Work, Energy, and Power

  • Energy consumed by humans is converted to work, thermal energy, and stored fat.
  • Work done by a person is sometimes called useful work, which is work done on the outside world, such as lifting weights.
  • Useful work requires a force exerted through a distance on the outside world, and so it excludes internal work, such as that done by the heart when pumping blood.
  • The work going into mechanical energy is W= KE + PE.
  • Energy consumed by humans is converted to work, thermal energy, and stored fat.

• Force in the Direction of Displacement

  • The work done by a constant force is proportional to the force applied times the displacement of the object.
  • When a force acts on an object over a distance, it is said to have done work on the object .
  • The SI unit of work is the newton-meter or joule (J).
  • Often times we will be asked to calculate the work done by a force on an object.
  • Calculate the work done on the box if the box is displaced 5 meters.