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When an object rests on a slope, like a ramp or a hill, we refer to this scenario as an inclined plane. Gravity always pulls objects directly downwards towards the Earth, which we call a vertical force. However, when an object is on an inclined plane, not all of this gravitational force acts perpendicular to the surface. Instead, the gravitational force can be separated into two components: one parallel to the incline and one perpendicular to it.

• The parallel component pulls the object down the slope.
• The perpendicular component interacts with the surface to create the normal force.

The normal force acts at a right angle to the surface of the incline, rather than vertically. Since the object doesn't need support for the entire force of gravity (only the perpendicular component), the normal force is usually less than the object's weight.
This is a common situation in physics, often represented by the equation \( N = mg \cos \theta \), where \( \theta \) is the angle of the incline. Hence, the normal force adapts to the orientation of the surface.

When an object is involved in motion that is strictly up and down, we call this vertical motion. Imagine a person standing in an elevator that ascends upwards. In this scenario, the person (or object) experiences various forces acting on them:

• Gravitational force pulling them down.
• An additional force because of the elevator’s upward acceleration.

Under normal circumstances, gravity is countered by an equal upward force, often the normal force that a surface provides. However, with the elevator moving upwards, the situation changes. The normal force increases to not just hold the weight of the person, but also to counter the upward pull due to acceleration.
Hence, the normal force in this situation is greater than the gravitational force acting on the object, represented as \( N = m(g + a) \), where \( a \) is the elevator's acceleration.

Gravitational force is one of the fundamental forces of physics and explains why objects are attracted towards the center of the Earth—or any massive body. It acts on all objects with mass and exerts a pull towards the center of the Earth.
This force is what keeps us grounded and gives weight to any object, calculated as \( F = mg \), where \( m \) is the mass, and \( g \) is the acceleration due to gravity, approximately 9.8 m/s² on Earth.
While gravitational force always acts vertically downwards, its effect can vary based on the object's environment or movement. For example, it can affect:

• A skydiver in free fall experiencing gravity as the only force.
• An airplane where engines counterbalance gravitational pull for horizontal movement.

In every case, gravitational force is ever-present but its interaction with other forces, like normal force, can alter how we perceive an object's motion and support.