Newtonian Mechanics and Forces

Friction is a force that opposes motion between two surfaces in contact. It acts in the opposite direction to movement, which is why it can slow down or stop moving objects. Electricity and petrol are energy sources, while acceleration increases speed rather than reducing it.

Gravity is the force that holds us to Earth by pulling objects toward the planet's center. Temperature is a measure of thermal energy and has nothing to do with gravitational attraction.

The four fundamental forces of nature govern all interactions in the universe. The strong nuclear force holds atomic nuclei together, while the weak force is responsible for radioactive decay. Gravity acts on mass across cosmic distances, and electromagnetism mediates interactions between charged particles.

In pure rolling on a horizontal surface with no external forces (like air resistance or an applied torque), the acceleration is zero. Therefore, no friction is required to maintain the rolling state, and the static friction is zero.

Newton's first law of motion (law of inertia) states that an object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force. All options A-D describe different aspects of this law, making E the correct comprehensive answer. Option A describes the rest case, B describes motion in straight line, C adds constant velocity (same speed and direction), and D describes the rest condition.

According to Newton's first law of motion, an object in motion will continue in motion at a constant velocity in a straight line unless acted upon by an external net force. On a frictionless surface, no horizontal force is needed to maintain motion.

Inertia is indeed the property of matter that causes it to resist any change in its state of motion. Objects with more mass have more inertia - they're harder to start moving, stop moving, or change direction. This is why a heavy truck is harder to stop than a bicycle moving at the same speed. The definition given in the question is accurate.

Once the wrench is thrown in space, it will continue moving indefinitely without any additional force needed. This is Newton's first law of motion in action - in the vacuum of space with negligible forces acting on it, the wrench will maintain its velocity without requiring force to 'keep it going'. The force was only needed to throw it initially, not to maintain its motion.

Newton's first law (law of inertia) states that objects resist changes in motion - a resting object stays at rest, and a moving object continues with constant velocity unless acted upon by an unbalanced external force. Options A, B, and C correctly describe this principle. Option D is false because a body CAN move at constant speed with an external force if the force is perpendicular to motion (like circular motion), or if balanced forces act on it.

When a body rests on a horizontal surface without external forces, two forces act on it: its weight (downward) and the normal reaction force (upward) from the surface. Since the question specifically asks about forces from the ground/surface, 'normal reaction' (B) is the correct answer. Friction only acts when there's motion or tendency to move.

This statement accurately describes subduction, which occurs at convergent plate boundaries. When a dense oceanic plate converges with a less dense continental plate, the oceanic plate is forced beneath the continental plate and into the mantle. This process creates deep ocean trenches, volcanic arcs, and can cause powerful earthquakes. The subducting plate melts as it descends, creating magma that rises to form volcanoes.

Fluid friction (drag force) is directly proportional to relative velocity at low speeds (Stokes' law: F = 6πηrv) and proportional to the square of velocity at higher speeds (F = ½ρv²CdA). It is never inversely proportional to speed - as speed increases, drag force always increases, not decreases. Therefore, the statement is false.

Rolling friction is significantly less than sliding friction because rolling involves less surface contact area between surfaces. When an object rolls, only a small portion of its surface touches the ground at any instant, reducing friction. Converting from sliding to rolling (like using ball bearings or wheels) is a fundamental principle in mechanical design to reduce energy loss and improve efficiency.

Frictional force is the odd one out because it is a contact force that requires physical contact between surfaces, whereas gravitational, electrostatic, and nuclear forces are fundamental non-contact forces that act at a distance. The other three are fundamental forces of nature, while friction is a derived force.