Turning a lawn mower My initial doubt was if it is easier to turn a lawnmower while pushing it or pulling it?
I thought that friction would provide a centripetal force (just like when we turn tires) and it more in case of pushing. So it is easier to turn while pushing.
Please help me correct this.
 A: It depends on how you push/pull the lawnmower specifically. Friction depends on the normal force to the ground. So if you manage to push (pull) by a strictly horizontal force, you will induce a torque, but your additional total normal force component will be zero. The only effect of the torque will be to increase (decrease) the force on the front wheels, and decrease (increase) the force on the back wheels, but the total force remains zero, as already mentioned. Hence, friction will not be different, whether you push or pull the thing.
However, if you push it with a slight angle towards the ground, which is probably regularly so for a person taller than the lawnmower's handle, then a total normal force is induced, which increases friction. When pulling at the same angle, the sign of this additional normal force changes, and so friction gets decreased.
Turning the lawnmower is by no means different from a linear motion. The wheels at the outer circle move a little longer way, while the wheels at the inner circle move a little shorter way, but the average arc length stays the same. So if you push the lawnmower at an angle, it is a little more difficult to turn it (as it is to move it on a straight line), while it is a little easier when pulling it.
Caveat: there might be an additional "friction" force due to the force needed to cut the grass leaves. A naive consideration lets me think that the force is transversal to the direction of motion of the lawnmower, because the leaves get cut forward on one side and backward on the other side, so the forward/backward forces cancel and only side cutting forces remain.
However, aerodynamic effects (swirling of the grass leaves) might cause certain longitudinal cutting forces as well (e.g if the swirling leaves prefer to be cut where the cutting blades move backward). If you pull the lawnmower back after having pushed it for a while, all the leaves there are already cut and hence, the cutting forces will then be zero when pulling.  But not if you pull it where leaves of grass are still standing! That is, it might also depend on the history of the trajectory, what you have to expect from pushing/pulling.
A: In general it is easier to pull a (four wheeled) lawnmower than to push since you are reducing the normal force with the ground, however for turning, a tangential (downward) force on the handle will lift the front wheels from the ground reducing friction to rolling on the rear wheels.
