When a car moves around a horizontal curve in a circular path, which type of force is responsible for changing its direction of motion?

Introduction / Context:
Objects moving in circular paths, such as cars on curved roads or planets in orbits, require a net inward force to continuously change the direction of their velocity. This net inward force is called centripetal force. This question asks which type of force is responsible for changing the direction of a car moving around a curve, reinforcing the concept of centripetal motion in everyday situations.

Given Data / Assumptions:

• The car is moving at some speed along a horizontal curved road.
• The curve is approximated as part of a circular path.
• The car tyres remain in contact with the road surface without slipping.
• Vertical motion is not significant; the main change is in horizontal direction.
• Friction between tyres and road can provide the necessary lateral force.

Concept / Approach:
For circular motion at constant speed, the direction of velocity continually changes, which requires an inward acceleration called centripetal acceleration. The corresponding net inward force is the centripetal force. In the case of a car on a flat road, static friction between the tyres and the road surface usually provides this centripetal force, directed toward the centre of curvature. Centrifugal force is a fictitious force that appears only in a rotating frame and is not the real cause of directional change in an inertial frame.

Step-by-Step Solution:
Step 1: Recognise that a car moving along a curve experiences a change in direction of velocity, which implies centripetal acceleration toward the centre of the curve.Step 2: Recall that the real force responsible for this acceleration is called the centripetal force.Step 3: In a simple model, static friction between tyres and road provides the horizontal inward force needed for centripetal motion.Step 4: Conclude that centripetal force is the correct term for the force changing the car direction as it moves around the curve.

Verification / Alternative check:
If the frictional force is too small, such as on an icy road, the car cannot obtain enough centripetal force and will skid outward instead of following the curve, confirming that a real inward force is needed to sustain circular motion. Equations for uniform circular motion, like centripetal force equal to m * v squared divided by r, show that higher speeds and tighter curves require larger inward force, matching driving experience where sharp turns at high speed are dangerous.

Why Other Options Are Wrong:
Option a is wrong because centrifugal force is not a real force in an inertial frame; it is a pseudo force used in the rotating frame of the car. Option b is incorrect since cohesive forces act at the molecular level inside materials and are not the macroscopic force causing the turn. Option d is not correct because gravity acts vertically downward and is balanced by the normal reaction; it does not change the car horizontal direction. Option e is wrong, as electrostatic forces between tyres and road are negligible compared to frictional forces and do not normally play a role in steering.

Common Pitfalls:
Students often say that centrifugal force pushes the car outward when rounding a curve, which reflects the experience of being thrown sideways but confuses the analysis in an inertial frame. It is better to concentrate on the real inward forces that cause the change of direction. Another pitfall is to overlook the role of friction, especially on banked or slippery roads. Always identify the inward directed real forces and label the net inward force as the centripetal force required for circular motion.

Final Answer:
Centripetal force directed toward the centre of the circular path.