Friction acting on box not slipping in truck

AI Thread Summary
When a truck accelerates forward, static friction acts on the box in the forward direction to prevent it from slipping. Although it seems counterintuitive, friction opposes the relative motion between the box and the truck. The box, wanting to remain stationary, experiences a backward motion relative to the truck, necessitating forward friction to keep it in place. A visual representation clarifies that while the truck moves forward, the box's inertia attempts to keep it still, requiring friction to push it along. Understanding this dynamic is key to grasping the role of static friction in accelerating systems.
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Sorry for not using the proper post format. I'm typing on my phone and the post template doesn't show up.

Question: a box is sitting in the back of a truck which accelerates forward when a traffic light turns green. Which of the following statements is correct if the boxdoes not slip?

The answer is: the force of static friction acts on the box in the forward direction.

I don't understand why it's in the forward direction. I thought friction was always in the direction opposite motion, and motion, in this case, is forward. Therefore, shouldn't the friction be acting backward?
 
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The truck goes forward but the wheels of the truck aren't attached to the box. The box wants to stay still and let the truck slip underneath it. Friction however decides to push the box and force it to stay on the truck.
Drawing a picture helps too.
 
The direction of motion of the car is forward, but the direction of motion of the box relative to the car would be backwards. Thus, friction must be in the forwards direction to keep the box from moving.
 

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