# Static Friction vs. Kinetic Friction: What's the Difference?

Edited by Huma Saeed || By Sumera Saeed || Updated on October 5, 2023
Static friction resists the initiation of motion between two surfaces, while kinetic friction opposes the ongoing motion between moving surfaces.

## Key Differences

Static friction emerges when two surfaces are not in motion relative to each other. This type of friction must be overcome to initiate movement, essentially acting as the force that holds objects stationary. On the contrary, kinetic friction, sometimes referred to as dynamic friction, manifests when two surfaces are sliding past each other, providing a resistive force against the motion already in progress.
Sumera Saeed
Oct 05, 2023
In practical applications, static friction is what keeps a parked car from sliding down a hill – it works against the gravitational pull. Once the car begins to move, kinetic friction takes over, opposing the sliding between the tires and the road. Thus, static friction prevents the initial slide, and kinetic friction opposes the motion once it has begun.
Sumera Saeed
Oct 05, 2023
Interestingly, static friction generally tends to be greater than kinetic friction for a given set of materials. This means that it often takes more force to initiate motion (overcoming static friction) than to keep it in motion (overcoming kinetic friction). As a practical observation, once an object is set in motion, it typically requires less effort to keep it moving, showcasing the role of kinetic friction as a slightly lesser opposing force.
Sumera Saeed
Oct 05, 2023
In physics, static and kinetic friction are described by the equations: F_s ≤ μ_sN and F_k = μ_kN respectively, where F_s is the maximum static frictional force, F_k is the kinetic frictional force, μ_s and μ_k are the coefficients of static and kinetic friction, and N is the normal force. These equations underline the core difference, where static friction provides a variable resistance up to a maximum threshold, and kinetic friction presents a consistent force once motion has commenced.
Sumera Saeed
Oct 05, 2023
From an experimental perspective, static friction can be observed in various day-to-day activities, such as pushing a heavy object from rest. It resists the initiation of movement until a sufficient force is applied. Kinetic friction, meanwhile, is witnessed once the object is in motion, providing a constant resistance that must be counteracted to maintain a steady movement, thereby illustrating practical encounters with these frictional forms in our daily lives.
Sumera Saeed
Oct 05, 2023

## Comparison Chart

### Definition

Resists the initiation of motion
Opposes ongoing motion
Sumera Saeed
Oct 05, 2023

### Occurrence

When objects are stationary
When objects are sliding past each other
Sumera Saeed
Oct 05, 2023

### Magnitude

Generally greater than kinetic friction
Generally less than static friction
Sumera Saeed
Oct 05, 2023

F_s ≤ μ_sN
F_k = μ_kN
Janet White
Oct 05, 2023

### Practical Example

Preventing a stationary object from moving
Slowing down a sliding object
Aimie Carlson
Oct 05, 2023

## Static Friction and Kinetic Friction Definitions

#### Static Friction

Inhibits the initiation of sliding between surfaces.
Static friction keeps the vase secure on the shelf.
Sumera Saeed
Oct 05, 2023

#### Kinetic Friction

Resistance against the continuous sliding of objects.
Kinetic friction between the skis and snow affects the skier’s speed.
Huma Saeed
Oct 05, 2023

#### Static Friction

A friction form resisting the start of relative motion.
Static friction stops the boulder from rolling down the hill.
Sumera Saeed
Oct 05, 2023

#### Kinetic Friction

Acting on objects already in relative motion.
Kinetic friction works against the moving skateboard.
Sumera Saeed
Oct 05, 2023

#### Static Friction

A friction type that acts on stationary objects.
Static friction holds the car in place on the sloped road.
Sumera Saeed
Oct 05, 2023

#### Kinetic Friction

Impedes the persistence of sliding among surfaces.
The kinetic friction between the sliding box and the ground will eventually stop it.
Harlon Moss
Oct 05, 2023

#### Static Friction

Resisting force against starting movement.
The static friction between the box and the floor must be overcome to start pushing it.
Huma Saeed
Oct 05, 2023

#### Kinetic Friction

A friction type hindering ongoing relative movement.
Kinetic friction resists the rolling motion of the tire across the pavement.
Sumera Saeed
Oct 05, 2023

#### Static Friction

Force that opposes initial motion.
Static friction prevents the book from sliding off the tilted table.
Sumera Saeed
Oct 05, 2023

#### Kinetic Friction

Force that opposes ongoing motion.
Kinetic friction slows down the sled as it slides down the hill.
Sumera Saeed
Oct 05, 2023

## FAQs

#### Can kinetic friction act on an object at rest?

No, kinetic friction only acts on objects already in motion.
Sumera Saeed
Oct 05, 2023

#### How are coefficients of static and kinetic friction determined?

They are determined experimentally, often using a tilted plane and observing at what angle an object starts to slide (static) or continues sliding (kinetic).
Sumera Saeed
Oct 05, 2023

#### Why does static friction not act on moving objects?

Static friction acts to prevent the initiation of motion, so it doesn’t act on objects already moving.
Sumera Saeed
Oct 05, 2023

#### Do materials with high static friction also have high kinetic friction?

Not necessarily, the relationship between static and kinetic friction coefficients can vary between materials.
Aimie Carlson
Oct 05, 2023

#### Can static friction occur without a normal force?

No, static friction depends on the normal force acting perpendicular to the surfaces in contact.
Janet White
Oct 05, 2023

#### Can static and kinetic friction be equal for certain materials?

Yes, in some scenarios or materials, the coefficients of static and kinetic friction may be very close or equal.
Janet White
Oct 05, 2023

#### How is rolling friction different from kinetic friction?

Rolling friction involves objects rolling over each other, while kinetic friction involves sliding, even though both involve motion.
Sumera Saeed
Oct 05, 2023

#### How does temperature affect static and kinetic friction?

Temperature can alter material properties, potentially changing the coefficients of static and kinetic friction.
Sumera Saeed
Oct 05, 2023

#### Why do we often shimmy or shake objects to overcome static friction?

Shaking can provide additional force or reduce the contact area, making it easier to overcome static friction.
Janet White
Oct 05, 2023

#### How do static and kinetic friction play roles in automotive braking?

Static friction helps keep a stationary vehicle in place, while kinetic friction acts to slow and eventually stop a moving vehicle when braking.
Sumera Saeed
Oct 05, 2023

#### Is static friction always higher than kinetic friction?

Typically, yes. Static friction usually requires more force to overcome compared to kinetic friction.
Huma Saeed
Oct 05, 2023

#### How do lubricants affect kinetic friction?

Lubricants usually decrease kinetic friction by reducing the interaction between sliding surfaces.
Sumera Saeed
Oct 05, 2023

#### Does air resistance impact kinetic friction?

No, kinetic friction pertains to surfaces in contact, while air resistance is a separate force.
Sara Rehman
Oct 05, 2023

#### Can an object be subjected to both static and kinetic friction simultaneously?

No, an object experiences static friction when at rest and kinetic friction once in motion, not simultaneously.
Janet White
Oct 05, 2023

#### Is it possible to have frictionless surfaces, thus eliminating static and kinetic friction?

While theoretically conceivable, practically achieving completely frictionless surfaces is nearly impossible.
Sumera Saeed
Oct 05, 2023

#### What is the basic difference between static and kinetic friction?

Static friction resists the start of motion, while kinetic friction opposes motion that’s already happening.
Sumera Saeed
Oct 05, 2023

#### In what units is friction measured?

Friction is a force, so it is measured in Newtons (N) in the International System of Units (SI).
Sumera Saeed
Oct 05, 2023

#### How does surface area impact static and kinetic friction?

Surprisingly, friction is independent of surface area as it's defined per unit area.
Janet White
Oct 05, 2023

#### Can zero-gravity environments influence static and kinetic friction?

While gravity affects normal force, which in turn affects friction, static and kinetic friction still occur in zero-gravity environments.
Janet White
Oct 05, 2023

#### Why do we feel heat when we rub our hands together, in terms of kinetic friction?

The kinetic friction between our hands converts mechanical energy into thermal energy, creating heat.
Sumera Saeed
Oct 05, 2023