Newton's Law of Gravitation
Earth and Space

Gravity gets stronger

Teaching Guidance for 11-14 Supporting Physics Teaching

Higher means stronger

Wrong Track: Gravity gets stronger the higher up you get.

Right Lines: If this statement was true, it would get harder and harder to escape from the Earth. However, pictures of a Space Shuttle taking off show that the largest force is required at the beginning and as you get farther from Earth, smaller rockets are required. The force gets weaker the larger the distance between the objects.

Height and falling speed

Thinking about the learning

Some pupils believe that gravity increases with height.

This wrong track idea is likely to be based on observations that if an object (such as a brick) is dropped from a greater height, then it has a bigger impact on hitting the ground. This is true but it's because the additional height increases the energy in the gravity store (which is augmented as the brick is dragged away from Earth) and not the gravitational force acting on the brick.

Newton's Law of Gravitation
is expressed by the relation F=G(m_1)(m_2)/r^2
can be used to derive Kepler's First Law

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