Newton’s Law of Gravitation Flashcards
Describe how gravitational attraction varies with distance Explain what is meant by an inverse-square law Discuss weather spherical objects, for example planets, can be treated as point masses
What causes a planet to orbit the Sun?
A force of gravitational attraction between the planet and the Sun
How does gravitational attraction vary with distance?
Gravitational force varies inversely with the square of the distance apart
- as distance increases GF decreases at a rate proportional to the square of that distance
What is meant by an inverse-square law?
Where a quantity decreases in proportion to the square of the distance from the source
Why is it reasonable to consider the Sun and the Earth as point masses on a scale model?
On a model where the Sun is 1m away from the centre of the earth,
- Sun - diameter = 1cm
- Earth - diameter = 0.1mm
- the distance from the Earth to any part of the sun is the same within 1%
- Therefore can be treated as point masses
State the assumptions of Newton’s Law of Gravitation
The gravitational force is
- always attractive
- proportional to the mass of each object
- proportional to 1/r2, where r is the distance apart
State Newton’s Law of Gravitation
F = - GMm/r2
What is G?
The universal constant of gravitation
State the equation of g
g = -GM /r2
State the relationship between g and r inside and outside of a planet
Inside: g proportional to r
Outside: g is proportional to 1/r2
