Does Running or Walking the Same Distance Use More Energy?

[ddelaiarro]

You'll have to excuse me if this issue has been discussed here before. I did about 30 minutes worth of searching and didn't come upon it, so I decided to post.

A colleague and I had a lengthy discussion today on whether running a set distance spends more calories (energy) than walking that same distance.

My main argument centered around moving a mass over a distance.

My contention is that work is the product of force and distance:

W = F * d

If the same mass, m, is moved across the same distance, d, then the same force, F, is exerted. The hinge point of my argument is the assumption that your acceleration/deceleration is instantaneous.

If you look at the free body diagram, you'll note that you have force acting in two axis on the mass.

In the x-axis, you have the applied force, F, and the friction force, F_f. According to Newton's Second Law, a body in motion will stay in motion unless acted upon. Hence, in order to keep a constant velocity,

F = F_f hence $$\Sigma$$ F_x=0

In the y-axis, there's a gravitational force,

F_g = m * g

and the equal and opposite normal force, F_N


F_g = F_N hence $$\Sigma$$ F_y=0

The kinematic coefficient of fricition, u, is the same, regardless of velocity. The equation for friction force is:

F_f = F_N * u * cos(theta) <-- Theta being the angle at which the plane the mass is on is at. Assume a flat plain (cos0 = 1) for simplicity here.

Regardless of velocity, u and F_N are the same, hence F_f is the same.

So, if F_f is the same, F is the same. And, in the end,

W = F * d produces the same product regardless of velocity.

In the end, I convinced my coworker that my approach was correct. Although, he didn't buy the end result.

I'd love to hear some of your thoughts on this subject.

 

[gstrosx]

Consider the heat output from someone who just ran x vs someone who just caught up to that person by walking. The work done in transporting the body is the same (assuming exactly equal body masses) however there is other energy that is spent. You have to consider total energy difference, dE = dK + d(k*Temperature) in this case.

 

[astrokreng]

Dear colleague,

Thank you for bringing up this interesting topic. I agree with your argument that work is the product of force and distance, and that the same work is done regardless of the velocity at which the distance is covered. This is because the force and distance remain constant, and according to the laws of physics, work is only done when there is a displacement in the direction of the applied force.

However, I also understand your colleague's skepticism about the end result. It is important to consider that while the work done may be the same, the energy expenditure may not necessarily be equal. This is because the human body has different energy requirements for different activities, and the intensity and duration of the activity can also affect the amount of energy expended.

For example, running may require more energy expenditure than walking due to the increased effort and intensity involved. Additionally, the body may also adapt and become more efficient at certain activities, leading to a decrease in energy expenditure over time.

In conclusion, while your argument about work and velocity is valid, it is important to also consider other factors that may affect energy expenditure. I hope this helps in your further discussions on this topic.

Best regards,