Question

A: when an object is placed on a surface the frictional force between the surface and the object is more if the mass of the object is heavy. R: static friction is directly proportional to normal reaction.

When a car negotiates a curved road, the force of friction between the road and the tyres provides the centripetal force required to keep the car in motion around the curve. A large amount of friction between the tyres and the road produces considerable wear and tear on the tyres. To avoid dependence on friction, the curved road is given an inclination sloping upwards towards the outer circumference. This reduces the wearing of the tyres because the horizontal component of the normal reaction provides the necessary centripetal force. The system of raising the outer edge of a curved road above the inner edge is called the banking of the curved road. When a vehicle negotiates a circular turn of radius r and is banked at an angle θ, the maximum safe velocity is given by vmax = rg tanθ the absence of frictional forces vmax = √rg (μS + tan θ) / (1 - µS tan θ), in the presence of frictional forces.

Whenever a body moves or tends to move over the surface of another body, a force comes into play which acts parallel to the surface of contact and opposes the relative motion. This opposing force is called friction. Static friction fS opposes the impending relative motion while the kinetic friction fK opposes the actual relative motion. Static friction is a self-adjusting force. The maximum value of static friction (fS=μsN) which comes into play when a body just starts moving over the surface of another body is called limiting friction. fs ≤ μsN and fk = μkN where N is the normal reaction between the two surfaces in contact. Both static and kinetic friction are independent of the area of surfaces in contact.

A mass m is attached to a string of length r and is swung in a vertical circle. The mass is released from the top of the circle. The study focuses on the forces acting on the mass and the concepts of centripetal force, tension, and energy transformations.