In this second lecture on cosmology - and final lecture of the course - we first look at why curved spaces are candidates for possible cosmologies but why we can still assume that space is flat.

We then see how the density of matter and energy in the universe affects the rate of expansion, by using the Newtonian energy equation for projectile motion to calculate various forms of the scale factor.

In particular, we consider three models

- the matter-dominated universe
- the radiation-dominated universe (model for early universe)
- the vacuum-energy-dominated universe (model for today's universe)