Difficulty: Easy
Correct Answer: Frictional force
Explanation:
Introduction / Context:
Walking is such a common activity that we rarely think about the physics behind it. However, every step you take is governed by basic principles of mechanics. The question asks which force allows us to walk on the surface of the earth without constantly slipping. This concept is fundamental in mechanics and is closely related to friction, contact forces, and motion. Understanding it helps explain not only walking, but also why tyres grip the road, why shoes are designed with tread patterns, and why people slip more easily on smooth ice or wet floors.
Given Data / Assumptions:
Concept / Approach:
When you walk, you push your foot backward against the ground. According to Newton's third law, the ground exerts an equal and opposite force on your foot. This forward reaction force provided by friction between your shoe and the ground is what propels you forward. If friction is too low, such as on ice, the backward push does not create enough reaction force, and you slip. Gravitational force simply keeps you on the ground but does not prevent slipping along the surface. Viscous force is important in fluids, and centrifugal force appears in rotating reference frames. Therefore, the correct force that prevents slipping is frictional force.
Step-by-Step Solution:
Step 1: Recognise that walking involves interaction between your feet and the ground.Step 2: When you attempt to walk, your foot applies a backward push on the ground.Step 3: The ground responds with a forward force on your foot due to friction between the surfaces.Step 4: This forward frictional force accelerates your body forward, allowing you to move without slipping.Step 5: If friction is absent or very small, as on ice, your foot would slide backward instead of gripping, and you would slip. Therefore, frictional force is essential.
Verification / Alternative check:
You can verify this idea by thinking about situations where friction is reduced. On a polished floor or icy road, it becomes hard to walk without slipping. People often use shoes with better grip or sprinkle sand on icy paths to increase friction. Vehicles use tyres with tread patterns to increase friction with the road. In all these examples, the key quantity being adjusted is friction. Gravity remains the same, yet slipping behaviour changes with friction, confirming that frictional force is the controlling factor in walking safely.
Why Other Options Are Wrong:
Gravitational force pulls you downward and keeps your feet in contact with the ground but does not stop horizontal slipping, so option A is incomplete. Viscous force acts in liquids and gases and is not the main factor when walking on solid ground, so option C is incorrect. Centrifugal force is a fictitious force observed in rotating frames, such as in a turning car, and is not responsible for ordinary walking on a straight path, so option D is also wrong. Only frictional force correctly explains walking without slipping.
Common Pitfalls:
Many learners quickly choose gravitational force because they know gravity keeps us on the ground. However, the question asks specifically about slipping, which is a tangential or sideways motion along the surface. It is easy to overlook the role of friction in providing horizontal grip. Always read words like slipping, rolling, and skidding carefully, because they usually point towards friction related concepts rather than gravity alone. Also, remember that multiple forces can act at once, but the question asks which particular force allows walking without slipping, so you must identify the most relevant one.
Final Answer:
Frictional force
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