How would earth be affected if its orbit around the sun were slower or faster?
If the Earth's orbital speed were to change it would have to change distance from the Sun to stay in orbit.
The orbit of a planet is governed by Kepler's third law #T^2=a^3#. Where #T# is the orbital period in years and #a# is the semi-major axis distance in AU.
If the Earth were to travel faster in its orbit the period would be smaller and hence the distance must be smaller to stay in orbit.
Likewise it it travelled slower the distance must be greater to stay in orbit.