# Friction Direction Question

1. Aug 4, 2010

### jofree87

Problem states that a panel sits against a rough horizontal surface and smooth vertical surface on a truck that is decelerating at 4m/s^2. The solution has the force of friction pointing to the right. Can somebody explain why its not pointing to the left? If the horizontal surface were frictionless wouldn't the panel slip to the right if the truck moved backwards?

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2. Aug 4, 2010

### pgardn

Have you given us all the info? Is the truck moving to the right but accelerating to the left?
Is the truck moving backwards (to the left) and accelerating to the right? When it says decelerating, that implies negative acceleration. So in this picture is the right positive and the left negative as is normally the case on a horizontal number line? Need some reference here...

3. Aug 4, 2010

### jofree87

The problem doesn't state whether the truck is at rest or not, I just figured deceleration would mean the truck accelerates backwards, to the left.

btw I could see why the friction would point to the right if the truck were at rest, but if the truck was accelerating backwards (left), I would guess friction points forward to the the right?

4. Aug 5, 2010

### pgardn

If the truck was moving to the right, and accelerating to the left (slowing down) and the ladder were to remain at the same angle as shown in relation to the truck, friction would have to oppose the normal force drawn at the top of the ladder, otherwise the ladder would rotate I would think. If the ladder did rotate counter clockwise, there is no way friction would be pointed towards the right as friction would have to oppose the rotation at the bottom of the ladder. My thoughts. someone may want to add more.