How Friction helps in walking?-explanation with a free body diagram

Last updated on November 16th, 2023 at 01:44 pm

“If Friction is a force that opposes motion then how friction helps in walking?” As we walk we apply a contact force on the surface below and that surface also exerts an equal and opposite contact force on our foot or shoes. Depending on the position and angle of our foot, this reaction contact force applied on our foot helps us to move forward as well as saves us from slipping and falling. This is how friction helps walking, in simple words.
The above-said answer can be easily understood if we take the help of the Free Body Diagram and Vector Resolution of contact Forces.

How friction helps in Walking – 2 major steps

Our walking consists of a series of different steps among which we have selected two major steps that really take the help of Friction to have a balanced stature and then move forward.

From these 2 steps, it will be clear how friction helps us in walking or how friction is useful sometimes.

Step 1 – How friction provides the forward push to move ahead

• As we apply a force F on the floor (see Fig 1), the ground exerts an equal and opposite force F1 as per Newton’s third law of motion.
• That means, F1 = – F . Here F1 is the reaction force of applied force F.
• Now using Vector Resolution of force, let’s resolve the applied force F and the reaction force F1 one by one.
• (a) Applied force F is resolved into 2 components. The perpendicular downward component acts as the Weight W. And the horizontal component acting backward is the horizontal effective push given by the foot on the floor.
• (b) Now let’s resolve the Reaction force F1 into 2 components.
• Its perpendicular component (shown as N in the figure) is the Normal reaction. The horizontal component acts as the Friction F_R.
• So you can see very easily that Friction (F_R) just acts horizontally in the opposite direction of the effective horizontal push mentioned in the above section. This Friction (F_R) supplies the forward push to move ahead while walking.

Step 2 – How friction helps to balance and avoid slipping

• In step 2 the position of the foot is different than in step 1.
• It’s more of an effort to balance the position.
• As we apply a force F on the floor (see Fig 2), the ground exerts an equal and opposite force F1.
• Here also, F1 = – F . Here F1 is the reaction force of applied force F.
• Now using Vector Resolution of force, let’s resolve the applied force F and the reaction force F1 one by one as we did in step 1.
• (a) Applied force F is resolved into 2 components.
• The perpendicular downward component acts as the Weight W. And the horizontal component acting forward is the horizontal effective push given by the foot on the floor.
• This horizontal push, if not counterbalanced, will make us slip and fall. But fortunately, friction is there to counterbalance this. (see the section below:b)
• (b) Now let’s resolve the Reaction force F1 into 2 components.
• Its perpendicular component (shown as N in the figure) is the Normal reaction. The horizontal component towards the reverse/backward direction here acts as the Friction F_R.
• So you can see here also that Friction (F_R) acts horizontally in the opposite direction of the effective horizontal push.
• But in this case, the Friction (F_R) supplies the backward balancing push to avoid slipping while walking. See here how friction is useful sometimes.

How is friction useful sometimes? – Friction is a necessary evil

• Many times Friction causes lots of damage, but there are cases where friction comes up as a savior.
• We can easily explore multiple steps involved in the walking process and draw Free Body Diagrams (FBD) for each to understand how different force components play in the walking process and how and where Friction helps in walking.
• From this example (walking) we can easily conclude that Friction is a necessary evil.

Conclusion: Friction helps in walking

• We have seen that friction helps us to provide a forward push to move ahead while walking.
• Friction also supplies a backward balancing force which helps us to balance and not slip while walking.
• This simply shows how friction helps us in walking. This also explains that friction is useful sometimes!

Read another relevant post on friction here:

Pushing a car

Newton’s third law of motion