# It is easier to pull a lawn mower than push it. why?

2
by HariPardha

2015-08-20T21:36:00+05:30

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The ease with which you push or pull depends on the amount of friction acting on it.

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.
2015-08-21T01:06:21+05:30

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Lawn mover - pulling or pushing

When we pull a lawn mover, the force exerted is directed outwards from the ground along the lawn mover handles.  The force F applied through hands, is inclined at an angle Ф to the (horizontal) ground.  Let the lawn mover have a mass m.

The normal reaction N of the ground on the lawn mover will be
N = m g - F SinФ
Due to reduced normal reaction, the friction (static or kinetic) Ff between the lawn mover and the ground will be reduced from  μ m g to  μ (m g - F Sin Φ).  Hence it is easy to move it along the ground.  The net force  F Cos Φ - μ (mg - F Sin Φ) along the horizontal helps the movement of the lawn mover smoothly.  Only thing is one needs to move backwards.

net horizontal force = F (cos Φ +μ Sin Φ) - μ m g  to drive the lawn mover
Minimum  Force to be applied by us to just move it, F =  μ m g /(Cos Φ + μ Sin Φ)

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When we push the lawn mover along the inclined handle, the force applied is directed into the ground.  The normal reaction on the lawn mover by the ground is now =  N =  (m g + F Sin Φ).   Hence the force of kinetic or static friction increase to Ff =  μ (m g + F Sin Φ).  So it is more difficult to move the lawn mover along the ground.  The force F Cos Ф must be more than Ff.
the net horizontal force to drive lawn mover = F Cos Φ - μ mg - μ F Sin Φ
= F (Cos Φ - μ Sin Φ) - μ m g
Clearly this force is much less compared the force available in case of pulling the lawn mover.

Minimum Force to be applied by us to move it = F = μ m g / (CosΦ - μ SinΦ)
Clearly this is more than in case of pulling the lawn mover.

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