How does the gravitational field strength vary with altitude?

The gravitational field strength decreases as altitude increases.

The gravitational field strength, often referred to as 'gravity', is the force of attraction that a planet or other body exerts on objects in its vicinity. On Earth, this force pulls everything towards the centre of the planet. The strength of this force is determined by two factors: the mass of the planet and the distance from the centre of the planet.

The Earth's gravitational field strength is approximately 9.8 N/kg at sea level. This means that for every kilogram of mass, the Earth pulls it with a force of 9.8 Newtons. However, as you move away from the Earth - that is, as your altitude increases - the gravitational field strength decreases. This is because the force of gravity is inversely proportional to the square of the distance from the centre of the Earth. In simpler terms, the further away you are from the Earth, the weaker the force of gravity.

For example, at an altitude of 10,000 kilometres above the Earth's surface, the gravitational field strength is only about 1.5 N/kg. This is why astronauts in orbit around the Earth experience 'weightlessness' - they are still being pulled towards the Earth by gravity, but the force is much weaker than it is on the surface.

It's important to note that the decrease in gravitational field strength with altitude is not linear. The rate of decrease gets slower the further you go from the Earth. This is because the force of gravity follows an inverse square law - if you double your distance from the Earth, the gravitational field strength decreases by a factor of four.

In conclusion, the gravitational field strength decreases as you increase your altitude, due to the inverse square law of gravity. This is why objects weigh less at higher altitudes and why astronauts experience weightlessness in orbit.