Rolling friction that acts when a body rolls over a surface is primarily caused by which of the following?

Introduction / Context:
Friction plays a crucial role in everyday motion. While sliding friction is often discussed, rolling friction, which acts when wheels or balls roll over surfaces, is also very important in engineering and physics. This question asks about the main physical cause of rolling friction, a subtle concept that goes beyond the simple idea of surfaces rubbing against each other.

Given Data / Assumptions:

• A rigid body such as a wheel, cylinder or ball is rolling over a surface.
• There is some resistance to rolling motion, known as rolling friction or rolling resistance.
• We must choose which factor best explains this resistance among non-elastic effects, gravity, power dissipation or buoyancy.
• We ignore sliding friction and assume pure rolling without slipping at the point of contact.

Concept / Approach:
In an ideal world with perfectly rigid bodies and surfaces, a wheel rolling without slipping would experience no energy loss due to friction at the point of contact, and rolling friction would be zero. In reality, both the wheel and the surface deform slightly due to the load. These deformations are not perfectly elastic, meaning that some energy is lost in each cycle of compression and recovery. This non-elastic behaviour, often called hysteresis loss, is the primary cause of rolling friction. Gravity provides the normal force but does not by itself explain friction, and “power dissipation” is a result rather than a cause. Buoyancy acts in fluids, not in typical rolling situations on solid ground.

Step-by-Step Solution:
Step 1: Recognise that as a wheel or ball rolls, the part in contact with the surface is slightly flattened due to the load. Step 2: Both the rolling body and the surface undergo elastic and plastic deformation at the contact zone. Step 3: Because the materials are not perfectly elastic, they do not recover all the energy stored during deformation; some energy is lost as heat. Step 4: This non-elastic behaviour leads to a small resistive torque that opposes rolling, which we perceive as rolling friction. Step 5: Hence, non-elastic effects in the materials are the main cause of rolling friction.

Verification / Alternative check:
Engineers who design tyres, bearings and road surfaces pay close attention to material properties such as elasticity, hysteresis and internal damping because these control rolling resistance. Experiments show that wheels made from very elastic materials and running on smooth, rigid surfaces have significantly lower rolling friction. This observation is consistent with the idea that reduced non-elastic deformation lowers rolling resistance. Gravity is still present in these experiments but does not change, whereas changes in material elasticity clearly change rolling friction.

Why Other Options Are Wrong:
Gravity: Gravity provides the normal force and influences how strongly two surfaces press together, but it does not directly cause rolling friction.

Power dissipation: This is a consequence of friction, not a fundamental cause. Rolling friction leads to power dissipation, not the other way around.
Buoyancy: Buoyant forces act on bodies immersed in fluids and are unrelated to the friction encountered in normal rolling motion on solid surfaces.

Common Pitfalls:
Students sometimes think of friction only as a product of roughness and forget that deformation and material properties also play a role. Another mistake is to pick “gravity” whenever normal forces are involved, even though gravity alone does not explain why energy is lost in rolling. The key idea to remember is that rolling friction arises mainly from non-elastic deformations and internal energy losses in the materials at the rolling contact.

Final Answer:
Rolling friction is primarily caused by Non-elastic effects in the rolling body and the surface.