Question

why is it easier to pull a lawn mower than to push it

Answer 1

When you pull with a force F, the vertical component of force will be upward. So the net vertical force will be less than weight of lawn mower. So the normal force will be less(N = mg - F sinФ, where Ф is the angle with which you are pulling) and hence friction will  be less. When you push with a force F, the vertical component of force will be downward. So the net vertical force will be more than weight of lawn mower. So the normal force will be more(N = mg + F sinФ, where Ф is the angle with which you are pushing) and hence friction will  be more. So pulling is easier than pushing.