Is Work Directly Related to Time in Physics?

In summary, the definition of work is not explicitly related to time, but it can be calculated using the formula W=Fs. The force applied to an object can be either the net force or any applied force. The work done by an object is the product of the force and the distance traveled. In a scenario where the car hits a wall, the work done is equal whether the car decelerates rapidly or gradually over a longer distance. The work done is dependent on the force applied and the distance traveled, but not on the time it takes.
  • #1
96
1
I just read that the definition of work is not related whatsoever to the notion of time, whereas the relation between time and work is expressed by the explicit notion of power. However, W=Fs, and F is proportional to the acceleration a, which is the change of rate of the velocity wrt time.

Could you clarify this? Is the solution merely that the work W is not EXPLICITLY dependent on time?
 
Physics news on Phys.org
  • #2
gentsagree said:
However, W=Fs, and F is proportional to the acceleration a,
F is not the net force, but any force applied to an object.

gentsagree said:
Is the solution merely that the work W is not EXPLICITLY dependent on time?
It is nor defined via time. But of course you can compute the time for some energy transfer, given some extra information.
 
  • #3
I don't agree with your first reply: F can be taken as the net force [check page 186 of Young and Freedman, for one].

Regarding the second point: I know it is not defined via time, I am just pointing out (naively, I know, but I'd like a better understanding) that implicitly in the notion of work we have that of time. Not only that, it is changing time, so something like Delta t.
 
  • #4
gentsagree said:
F can be taken as the net force
It can, but it's not in general. You can't make general statements based on special cases.
 
  • #5
gentsagree said:
I don't agree with your first reply: F can be taken as the net force [check page 186 of Young and Freedman, for one].
You're both right (or more accurately, correctly describing subtly different things).

The total amount of kinetic energy imparted when moving an object is the net force times times the distance. In many problems that's the useful work done and the only thing we care about.

However, if the net force is the sum of multiple opposing forces, the total amount of work done may be much greater. For example, if you are pushing an object at constant speed against the force of friction, the net force is zero and the kinetic energy of the object doesn't change; but you're clearly doing work and the energy ends up as waste heat.

I am just pointing out (naively, I know, but I'd like a better understanding) that implicitly in the notion of work we have that of time. Not only that, it is changing time, so something like Delta t.
I don't see this. Apply a force of 100N over a distance of 100 meters and you've done 10,000 Joules of work. It doesn't matter whether it took a millisecond or a century to cover that distance, the work done is the same.
 
  • #6
Nugatory said:
I don't see this. Apply a force of 100N over a distance of 100 meters and you've done 10,000 Joules of work. It doesn't matter whether it took a millisecond or a century to cover that distance, the work done is the same.

I was thinking of this example: the velocity of a car which hits a wall goes from, say, 80 to 0 km/h almost instantaneously (quite disastrously). The force applied is then F=ma, where the acceleration is great since it happened over the space of a very short time interval. The work the brakes did is then W=Fs.

If the car gradually decelerates from 80 to 0, in say 10 seconds, the acceleration is much smaller. Hence the force and the work exerted by the brakes decrease.

This is why I was thinking that, implicitly, the work depends on time. Am I wrong?On a different note, please disregard my original comment on power: that's a completely different thing, just being the obvious description of how work is spread over time, thus a different aspect of time of what I wonder about.
 
  • #7
gentsagree said:
I was thinking of this example: the velocity of a car which hits a wall goes from, say, 80 to 0 km/h almost instantaneously (quite disastrously). The force applied is then F=ma, where the acceleration is great since it happened over the space of a very short time interval. The work the brakes did is then W=Fs.

If the car gradually decelerates from 80 to 0, in say 10 seconds, the acceleration is much smaller. Hence the force and the work exerted by the brakes decrease.

This is why I was thinking that, implicitly, the work depends on time. Am I wrong?
Yes, you are wrong. The net work done in both cases is the same and is independent of the time it takes for the car to be brought to rest. (In the second case, while the force is reduced the distance increases.)
 
  • #8
gentsagree said:
This is why I was thinking that, implicitly, the work depends on time. Am I wrong?
You can construct some scenario where some quantity depends on some other quantity. All physical quantities can be related somehow.
 
  • #9
I think you've misunderstood something somewhere along the line so:

Work = Force * Distance

for a constant force. For a variable force you use an integral.

In your example involving the car, the car has high Force and low Distance when it hits the wall. It has low Force and high Distance when it slows down over a longer distance. The work for the two operations must be equal.
 
  • #10
That's right. Thank you.
 
  • #11
For some weird reason I was convinced that the increase in acceleration and the decrease in distance weren't exactly proportional. All sorted then. Merci
 
  • #12
They are exactly proportional. You can try constructing a few scenarios of your own and working them out mathematically if you're not convinced. Have a nice day!
 

What is the relation between work and time?

The relation between work and time is that work is a measure of the amount of energy used to perform a task, while time is a measure of the duration it takes to complete the task. In other words, work is a product of force and distance, while time is a measure of how long the force is applied.

How does work affect the time it takes to complete a task?

The amount of work required for a task directly affects the time it takes to complete it. The greater the amount of work, the longer it will take to finish the task as more energy and effort are required. On the other hand, if the amount of work is reduced, the task can be completed in a shorter amount of time.

What is the relationship between work and productivity?

Work and productivity have a direct relationship, meaning that the more work that is done in a given amount of time, the higher the productivity. This is because productivity is a measure of how efficiently work is being done. Therefore, if more work is completed in the same amount of time, productivity will increase.

How can time management impact work productivity?

Time management plays a crucial role in work productivity. By effectively managing time, individuals can prioritize tasks, eliminate distractions, and efficiently use their time to complete work. This can lead to increased productivity as more work can be accomplished in a shorter amount of time.

What are some factors that can influence the relation between work and time?

There are several factors that can influence the relation between work and time, such as physical and mental abilities, environmental factors, and technological advancements. These factors can affect the amount of work that can be done in a given amount of time and the efficiency with which it is completed.

Suggested for: Is Work Directly Related to Time in Physics?

Replies
2
Views
846
Replies
1
Views
879
Replies
12
Views
1K
Replies
24
Views
2K
Replies
4
Views
858
Back
Top