Chapter 5: Applying Newton's Laws

Contact forces

Whenever two bodies interact by direct contact (touching) of their surfaces, we describe the interaction in terms of contact forces

Friction force

The component vector parallel to the surface is the friction force.

Kinetic friction force

The kind of friction that acts when a body slides over a surface is called a kinetic friction force.

Static friction

When a body is not moving relative to a surface, the friction force is called static friction.

What is the direction of the fluid resistance force acting on a body

The direction of the fluid resistance force acting on a body is always opposite the direction of the body’s velocity relative to the fluid.

Fluid resistance force for a small object at low speed

The magnitude f of the fluid resistance force is approximately proportional to the body’s speed v

f=kv

where k is a proportionality constant that depends on the shape and size of the body and the properties of the fluid.