Forces 02

Friction depends on both the nature of the two forces, and the _ force that a surface exerts on an object.

Normal force

Static friction

The frictional force between two surfaces that are not moving along each other when a force is applied but not enough to cause motion.

Static friction acts in the direction that…

…prevents slipping.

We can also say that static frictions acts in the direction that is _ to the surface.

tangent

The main “goal” of static friction is to keep objects on an incline from __ and __ when a force is first applied.

sliding and moving

The symbol for static friction is:

f_smax

Does the static frictional force increase or decrease as the applied force increases?

It increases.

Once the applied force exceeds the maximum of static friction (f_smax), the object will…

…start to move and kinetic frictional force (f_k) will take over.

Kinetic (sliding) friction

Once two surfaces begin sliding over one another, kinetic friction opposes the relative sliding motion that occurs.

The symbol for kinetic (sliding) friction is:

f_k

An object sliding down an incline has three forces acting on it; what are they?

The normal force, gravity, and the frictional force.

Equilibrium rule

The vector sum of forces acting on a non-accelerating object equals zero.

The equation form of the Equilibrium Rule:

$$\text{F}_{\text{net}} = 0$$

An object at rest is in…

…static equilibrium.

An object moving in a straight line at a constant speed is in…

…dynamic equilibrium.

In both static and dynamic equilibrium, there is…

…no Net Force acting on the object.