# Perpendicular force required to stop an object, with respect to friction

#### DanielAudi

1. The problem statement, all variables and given/known data
What force have to be applied to stop an polymer object with mass 5 gram and velocity 0.1 mm/s to stop in 0.2 mm? The polymer object touches a human skin at one side only, whereby friction Ff has a influence in the stopping process.

The object is moving to the left. In contrast to a normal problem, the stopping force is not a opposite one, but a perpendicular force. See image below.

_________________________________________ (human skin)
← □ (object moves with directon to the left)
↑ (perpendicular force - to the object and the human skin - to stop the object)

2. Relevant equations
F = ma

3. The attempt at a solution
To my knowledge, the formula F = ma is used to calculate the value of a opposite force to stop a object. Which formula do you use in case of a perpendicular force with respect to friction?

Many thanks!

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#### berkeman

Mentor
1. The problem statement, all variables and given/known data
What force have to be applied to stop an polymer object with mass 5 gram and velocity 0.1 mm/s to stop in 0.2 mm? The polymer object touches a human skin at one side only, whereby friction Ff has a influence in the stopping process.

The object is moving to the left. In contrast to a normal problem, the stopping force is not a opposite one, but a perpendicular force. See image below.

_________________________________________ (human skin)
← □ (object moves with directon to the left)
↑ (perpendicular force - to the object and the human skin - to stop the object)

2. Relevant equations
F = ma

3. The attempt at a solution
To my knowledge, the formula F = ma is used to calculate the value of a opposite force to stop a object. Which formula do you use in case of a perpendicular force with respect to friction?

Many thanks!
If friction is causing the stopping force (in the direction opposing the motion), then you use the equation for frictional force:

F = μ N

Where μ is the coefficient of friction, and N is the Normal force (the force pushing the object onto the skin in this case)...

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