Physics - Weight on Earth's Surface

Rotational Motion and Gravity

• The weight of a body measured on a weighing scale at the Equator compared with its weight measured on the same weighing scale at a pole would be smaller, because the gravitational attraction of the Earth must provide both the weight and the centripetal force due to the circular motion of the body.

Gravitational Force and Orbits

• The moon remains in its orbit around the Earth because the gravitational force exerted by the Earth on the moon provides a net force that provides the Moon's centripetal acceleration.
• A geostationary satellite can remain vertically above any chosen fixed point on the Earth, has the same angular velocity as the Earth's rotation on its axis, and its linear speed is equal to the speed of a point on the Earth's equator.

Forces in Orbit

• An object in a space capsule orbiting the Earth seems to be floating because the centripetal force on the object is equal and opposite to its weight.

Binary Stars

• The centripetal forces acting on the two stars in a binary system are equal in magnitude because the centre of their orbits is at a fixed point.
• The mass of each star in a binary system can be determined by using the period of their orbits and the separation of their centres.

Orbital Motion and Gravity

• The speed of a satellite moving in a circular orbit just above the surface of the moon can be calculated using the moon's mass and radius.
• The orbital period of a satellite can be calculated using the moon's mass and radius.

Gravitational Fields

• The neutral point in the gravitational field between two masses is the point at which the resultant gravitational field due to the two masses is zero.
• The acceleration due to gravity on a planet is affected by the planet's mass and radius.
• The mean density of a planet affects the acceleration due to gravity on its surface.