Friction and Drag

Topic 10.1

Friction

A force that acts parallel to the interface of two surfaces that are in contact, and opposes their relative motion

Coefficient of Friction

The ratio of the force of friction between two bodies and the normal reaction force

Static Coefficient of Friction

When a force is applied to attempt to move a stationary object over another surface

Dynamic Coefficient of Friction

When the force applied is sufficient to overcome the static friction and the object will being to move, once in motion, the coefficient is considered to be dynamic.

How can you minimise friction in sport?

• Sharpened ice skates, increase speed

• Waxing skis

• Sweeping, melts the ice in curling

How can you maximise friction in sport?

• Wearing spikes, e.g. in sprints

• Chalk, in gymnastics improves grip

Drag

The force(s) acting to oppose the motion of an object in a fluid medium

What are the types of drag?

Surface, form, and wave drag

Surface drag

Outer surface layer of a body catching fluid nearby, slowing it down.

Minimised by: wearing a tight fitting clothing, streamlined headgear

Form Drag

As a body pushes against a fluid, it pushes back

Minimised by: Changing the frame of a bike, crouching while cycling, maintaining a streamlined position while swimming

Wave drag

When a body moves along the surface of a fluid, some fluid is displaced, which creates waves that oppose motion

Minimised by: Swimming underwater for as long as possible

What factors influence drag?

• Fluid viscosity

• Surface size

• Shape

• Texture

• Relative velocity