Chapter 4: Gravity

What is Newton’s law of universal gravitation?

Any two bodies in the universe attract each other with a gravitational force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

F_g=G(m₁m₂₎/r²

F_g=gravitational force (N)

G= gravitational constant = 6.67×10^-11Nm²kg^-2

m1 and m2 = mass of object 1 and 2 (kg)

r is the distance between the centres of m₁ and m₂ (m)

Two bodies with masses 90 kg and 75 kg are at a distance of 80cm between

their centres. Calculate the force of gravitational attraction between them.

810N
Since F_N<F_g, person feels lighter.

Draw arrows to indicate the direction of the gravitational force acting at points

A and B.

State the relative strength of the gravitational fi eld at each poin

g can be written in units N kg^-1,look at stem of q.

9.62Nkg^-1

What is the gravitational field strength equation?

At an altitude above Earth’s surface = g=GM/(r+altitude)²

note convert to m.