FRICTION AND MAN: Walking isn't just biology, it's also PHYSICS.

The locomotion of most animals isn't just a function of the muscles bones and nerves in its body system. Man, according to biology, possesses certain muscles such as the quadriceps, hamstrings, hip adductors, etc. and bones such as metatarsals, tarsals, fibula, tibia, patella, etc. that work together to facilitate and support walking.
These parts definitely must receive the neurological walking commands from the brain through spinal nerves at the base of the spinal cord. _{see What Muscles, Bones and Nerves Are Involved When Walking?}

Exclusively, there is, more to walking than just this biology.


Let's discuss economics and psychology for a moment


Economics, alongside psychology has it that, the three basic needs of man are:
Food, which is required for good health and strength.
Clothing, which is needed for privacy and warmth.
Shelter, required for safety and protection from the external world.

This neglects the perspective of other fields like chemistry and physics about a man.


Relating these facts to physics.


Studies of friction, have it that one of its advantages is the locomotion of animals, to prevent slipping and falling.
It may sound immature; but, if friction never existed, how then is it possible for someone to walk from the roadside to his home? Or how possible will it be to have houses built, when nails require friction to remain in position in woods and walls? - This affects SHELTER.

Aside from these conditions, before and at a time during the evolution of man by natural selection, survival required the ignition of fires by rubbing two blocks of wood or pieces stone against each other for cooking and warmth- an effect of FRICTION.
What may have happened then if there was no friction?. This affects feeding and maybe, we would still be eating grasses. In addition, friction still supports lighting matchsticks and creating sparks in gas cylinders. _{see Why can't humans survive on grasses? by gentleshaid}

Consequently, in the extinction of friction, the neurological messages sent from the brain and the setup of the man's leg will be useless. Therefore, man needs friction.

FRICTION

Friction is a force produced along the common surface of two objects when one moves relative to the other. The frictional force opposes the force of motion. It is of two types namely, static friction and kinetic friction.

STATIC FRICTION prevents stationary bodies from moving. For the body to start moving, the force applied must overcome it's maximum, termed limiting friction.

KINETIC FRICTION occurs when limiting friction has been overcome. It acts in opposite direction to that of the motion of the body. It is usually lower than static friction. That's why it may take four men to push a vehicle from rest, and when it starts moving, only two can continue the push with ease.

So, how does friction actually support walking?

You may wonder, ''just the way friction opposes pushing a cabinet across the floor, why doesn't it oppose the forward motion of man?'' Why doesn't it draw a moving man backwards?

The answer is, ''it doesn't!''. Factually, it is what causes the forward motion.


Before you start moving forward, that is you are stationary, it would take a static forward frictional force to propel you. As you applied force on the ground with your foot to start moving, static friction is created between your foot and the ground. The ground produces this friction and pushes you forward.

You tried pushing the ground backwards by making use of those irregularities on the surfaces of your foot and the ground, and the ground, in turn, pushed you forward(action-reaction) from QUORA by Kishlay

_{See Newton's third law of motion}

Free Body Diagram of Friction Before Walking

_{FIG.1. original image by @synick}

In fig1, The force, F applied by the foot is in the third quadrant (negative X-axis and Y-axis), while the reaction, R acts in the first quadrant(positive X-axis and Y-axis)

Therefore, F = -R

With vector resolution of forces, F is resolved into two components, W-weight(perpendicular downward force) and P-push(Parallel-horizontal backward force). R also is resolved into two components, N-normal(perpendicular upward force) and F_r(horizontal forward force)

Therefore N = -W
F_r = -P

While walking and acceleration equals zero, that is velocity is uniform, the net/average friction is zero because its direction fluctuates-interchanges between forward and backward.
Backward friction is produced by the ground when you want to stop walking.

Free body diagram.

^{FIG.2. original image by @synick}

In fig 2
The applied force, F by the foot is in the fourth quadrant(positive X-axis and negative Y-axis), while the reaction, R acts in the second quadrant(negative X-axis and positive Y-axis)

Therefore, F= -R

Still, with vector resolution of forces, F is resolved to give W-weight(perpendicular downward force) and P-push(horizontal forward force), while R is resolved to give N-normal(perpendicular upward force) and F_r-friction(parallel backward force)

Therefore N = -W
F_r = -P

CONCLUSION

• Before walking, friction acts in a forward direction.

• While walking, net friction is zero.

• Immediately before walking stops, friction acts in a backward direction.

From this, I suppose you understand that friction is required everyday by man, especially in walking. Else, we slip and fall.

OTHER MERITS OF FRICTION

1. Sliding friction, on applying brakes, stops cars.

2. Friction makes writing easy.

3. Fluid friction - viscosity helps planes fly alongside the aerofoil._{See AN AIRPLANE'S FLIGHT MECHANISM}

4. It keeps nails fixed in walls and woods.

5. Igniting fires can be done with friction, etc.

References

• _Friction

• _{When we walk does frictional force act backwards or forward? QUORA}

• _{How Friction helps in walking?-explanation with free body diagram, 2017}

• _{Personal knowledge and notes}
  
  
  
  
  External links
  
  

• _{https://sciencing.com/list-advantages-friction-8726478.html}

• _{https://www.lifepersona.com/top-10-friction-advantages-and-disadvantages}

• _{https://www.livestrong.com/article/559413-what-muscles-bones-and-nerves-are-involved-when-walking/}
  
  

Note: Images used in this article are CC0 licensed and were properly sourced. Those credited to @synick are originals.
All external links in the article are for better understanding of anything confusing. All credits to their individual authors.

Thanks for reading. All arguments, debates, additions and questions, should be dropped below as a comment.

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