What is the definition of work done in physics and chemistry?
Work done is an abstract concept
You may hear your dad say he's going to work but according to the law of physics, your dad may not be doing any work at all! The definition says work is equal to force multiplied by distance, but the distance has to be in the direction of the force. So, if he merely sits in his office all day even if he's doing a lot of hard thinking, he isn't doing any work at all in physics term.
Formula for work done (in physics)
- According to the law of physics, Work done (W) = Force (F) x Distance moved (D)
- Work is done if you push your filing cabinet and the cabinet moves over a distance (D).
- If the cabinet is very heavy and doesn't move, then work done W = 0 no matter how hard you push the object because D = 0.
- Work done has to involve the displacement of force.
Work is not done when you carry an object forward
- You may have learnt that carrying an object and moving horizontally at a constant velocity has no work done.
- The truth is, there is a slight amount of work done due to overcoming air resistance in the horizontal direction.
- Also, when you accelerate and decelerate initially with the object, there's a slight amount of work done.
- However, in between work is not done because the distance moved is not in the direction of the force plus the fact that velocity is constant.
- The force acting on the object is actually upwards because its going against gravity holding the mass of the object. However, the distance the object is moved is horizontal, not in the direction of the force.
- So, we're not thinking about the man using up his energy holding the object. Rather, we're thinking about the force applied in the distance moved.
Work is done when you lift an object
When you lift the cabinet up from the ground, the force goes through a distance (H) above the ground, and when you put the cabinet down it also goes through a distance (H) to the ground.
When the cabinet is lifted up, the potential energy in the cabinet now is changed with the addition gravitational force acting on it. As an object is dropped from a height above ground in a position of rest, its gravitational potential energy is converted to kinetic energy.
Work is done when you carry an object upstairs
If you move your filing cabinet upstairs, in physics, work is done on your cabinet. So, if you move two floors up, there is a greater amount of work done than moving it up one floor.
Work done (in chemistry)
In chemistry, chemical reactions often produce gases that expand in the system. The definition of work done on the gas or by the gas is slightly different from moving solids around. However, the principal is still the same. If the expansion causes the volume of gas to change, then work is done. If there is no change in volume of gas in a chemical reaction, there's no work done.