Weight of an object is highest at the Poles because of the variation in the gravitational force due to the rotation and shape of the Earth.

Gravitational Force and Weight:
Gravitational force is the force of attraction between two objects due to their masses. Weight, on the other hand, is the force exerted on an object due to the gravitational pull of another object, in this case, the Earth. Weight is directly proportional to the mass of an object.

Gravitational Force and Earth:
The Earth is not a perfect sphere; it is slightly flattened at the poles and bulges at the equator. This shape is due to the Earth's rotation, which causes the equator to experience a centrifugal force pushing outward. Consequently, the shape of the Earth affects the distribution of mass, which results in variation in the gravitational force.

Gravitational Force and the Poles:
At the Poles, the distance between the object and the center of the Earth is the shortest. The gravitational force is inversely proportional to the square of the distance between two objects. Therefore, the closer an object is to the center of the Earth, the greater the gravitational force acting on it.

Gravitational Force and the Equator:
At the equator, the distance between the object and the center of the Earth is the greatest. As mentioned earlier, the Earth's rotation causes a centrifugal force at the equator that counteracts the gravitational force, resulting in a slightly lower net gravitational force compared to the Poles.

Conclusion:
In conclusion, the weight of an object is highest at the Poles due to the shorter distance between the object and the center of the Earth. This is because the gravitational force is stronger when the distance is shorter. Conversely, at the equator, the weight of an object is slightly lower due to the counteracting centrifugal force caused by the Earth's rotation.