Question

How do I pull a box with constant velocity? Since Fnet=0 means no acceleration, my pulling force has to be cancelled out by the friction, but that would mean the box would not move at all.

Answer 1

To pull a box with constant velocity, you need to apply a force that cancels out the force of static friction. The force of static friction opposes the motion of the box and prevents it from sliding.

When you apply a force to the box, the static friction force adjusts to match the applied force until it reaches its maximum value. Once the maximum static friction force is reached, the box starts moving with constant velocity. This maximum static friction force is given by:

$f_{\text{friction}}={\mu }_s\cdot N$,

where $f_{\text{friction}}$ is the force of static friction, ${\mu }_s$ is the coefficient of static friction between the box and the surface, and $N$ is the normal force exerted by the surface on the box.

To achieve constant velocity, you need to apply a force equal to the maximum static friction force in the opposite direction. This force can be calculated using the equation above. By exerting this force, you effectively cancel out the static friction force, resulting in a net force of zero and constant velocity.

It's important to note that the coefficient of static friction depends on the materials in contact. If the box is on a flat surface, the coefficient of static friction is typically greater than the coefficient of kinetic friction, which would allow the box to maintain constant velocity once it starts moving.

Keep in mind that other factors such as air resistance or uneven surfaces can affect the motion of the box, so it's essential to ensure that those influences are minimal or accounted for in your scenario.