You are Here: Home >< GCSEs

# Physics - Work done calculation is stupid

Announcements Posted on
Last day to win £100 of Amazon vouchers - don't miss out! Take our quick survey to enter 24-10-2016
1. It is really silly and inconsistent. The calculation is
Work done (J) = Force (N) x Distance (m)
This is why it's stupid:
If you are running on a treadmill with a running force of 10N you are effectively moving 0 m. So 10 x 0 = 0J
If you are running on flat ground with a running force of 10N and yuo run 50 m then the work done will be 10 x 50 = 500J

Theoretically, the work done should be the same but this just shows that the equation is flawed. I realise that it means the distance in m from the place that you start running from and this brings me onto another point.

The definition of speed is "The rate at which someone or something moves or operates or is able to move or operate"
When in actual fact speed is only the distance you travel in relation to another point in any given amount of time.

2. If you are running on flat ground you're moving through space at millions of metres per second. Therefore work done is millions of joules? No.

Your treadmill example is wrong. You ARE moving relative to the material on the treadmill surface. That's the distance travelled. It's all relative.

Anyway, work done is a scientific concept that is not 'inconsistent', it's just fact.
3. (Original post by BillyCockell)
It is really silly and inconsistent. The calculation is
Work done (J) = Force (N) x Distance (m)
This is why it's stupid:
If you are running on a treadmill with a running force of 10N you are effectively moving 0 m. So 10 x 0 = 0J
If you are running on flat ground with a running force of 10N and yuo run 50 m then the work done will be 10 x 50 = 500J

Theoretically, the work done should be the same but this just shows that the equation is flawed. I realise that it means the distance in m from the place that you start running from and this brings me onto another point.

The definition of speed is "The rate at which someone or something moves or operates or is able to move or operate"
When in actual fact speed is only the distance you travel in relation to another point in any given amount of time.

Work is done when a force is applied to an object and the object is moved through a distance. Your treadmill example is incorrect, it's like trying to apply Stoke's law to a large object moving in a turbulent flow (not possible to do btw).
4. It's displacement on a treadmill that is 0. You're still covering distance on the treadmill belt.
5. (Original post by Alexion)
If you are running on flat ground you're moving through space at millions of metres per second. Therefore work done is millions of joules? No.

Your treadmill example is wrong. You ARE moving relative to the material on the treadmill surface. That's the distance travelled. It's all relative.

Anyway, work done is a scientific concept that is not 'inconsistent', it's just fact.
But the surface of the treadmill will return back to it's original position and you are the same distance as you were before you started running from that position. And why is your first point wrong? That's what I was trying to get at, that distance and speed is only in relation to something.
6. Human body does a significant amount of work when it's 'doing nothing' -The human body is complicated, though it's tempting to apply all your physics principles to your own body because it seems familiar there's a lot more to be taken into consideration than you have done here.

even lying still in bed your body is doing work - holding a book out stationary with a straight arm is doing work

moving your legs rapidly backwards and forwards and jogging your centre of mass upwards against gravity on a treadmill... that sure as hell is doing work
7. (Original post by BillyCockell)
But the surface of the treadmill will return back to it's original position and you are the same distance as you were before you started running from that position. And why is your first point wrong? That's what I was trying to get at, that distance and speed is only in relation to something.
You are moving relative to the thing you're doing work on (the treadmill surface).
8. (Original post by Terry Tibbs)
You are moving relative to the thing you're doing work on (the treadmill surface).
are you actually doing much work against a treadmill belt (gym type) though? having used treadmills and run on the ground I'd say treadmills are a lot easier, partly I think cos you're bobbing up and down on the spot without building up any momentum so any corrective balancing movements you need to make are quite cheap in terms of energy.

if you removed the motor, held onto a fixed bar and pushed the belt around against some resistance with leg power that'd be applying force over the distance moved by the belt... but that's not how gym treadmills work, the belt is powered by a motor and just sets the pace you move your legs at afaik.
9. (Original post by Joinedup)
are you actually doing much work against a treadmill belt (gym type) though? having used treadmills and run on the ground I'd say treadmills are a lot easier, partly I think cos you're bobbing up and down on the spot without building up any momentum so any corrective balancing movements you need to make are quite cheap in terms of energy.

if you removed the motor, held onto a fixed bar and pushed the belt around against some resistance with leg power that'd be applying force over the distance moved by the belt... but that's not how gym treadmills work, the belt is powered by a motor and just sets the pace you move your legs at afaik.
But you are still doing some work against the treadmill belt to keep you in the same position. You would be doing more work if like you say there was no motor and you held onto the fixed bar, that would merely be the equivalent of you pushing a large box using friction between your shoes and the ground to move forward. A regular treadmill literally is the equivalent of normal running, the motor is there so that you're able to stay in the same position.

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: April 2, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

Poll
Useful resources

## Study tools

### Essay expert

Learn to write like a pro with our ultimate essay guide.

See where you can apply with our uni match tool

### Make study resources

Create all the resources you need to get the grades.

### Create your own Study Plan

Organise all your homework and exams so you never miss another deadline.

### Resources by subject

From flashcards to mind maps; there's everything you need for all of your GCSE subjects.

### Find past papers

100s of GCSE past papers for all your subjects at your fingertips.