what causes friction? even though a surface may look smooth, if you magnify the surface, you’ll...
Post on 26-Dec-2015
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What Causes Friction?Even though a surface may look
smooth, if you magnify the surface,
you’ll see it isn’t smooth at all.
Everything is made of molecules. The molecules come together to make bumps. Some surfaces have molecules that leave large bumps and some leave smaller bumps, but all surfaces have bumps.
Microwelds occur when two bumpy surfaces are rubbed up against each other and they stick together.
Friction is the force that opposes the motion between two surfaces that touch.The surface of any object is rough.Even an object that feels smooth is covered with tiny hills and valleys.The contact between the hills of valleys of two surfaces causes them to stick, resulting in friction.
What Causes Friction?
Different Types of ForcesFriction is just one of the forces we encounter daily. Here are a few of those forces and their symbols:
Gravitational Force (Gravity) – Fg
Applied Force - Fapp
Normal Force (acts perpendicular to surface) – Fn
Frictional Force (Friction) – Ffr
Air Resistance – Fair
Net Force – Fnet
Helpful and Harmful
Friction allows us to “push off” when we walk, and allows brakes to stop our cars. Friction is sometimes called “traction”.
Friction can cause wear on surfaces in an engine, or rip a hole in our jeans when we fall.
Types of FrictionFriction – force that opposes the motion of objects that touch as they move past each otherContact force – “touching”4 Main Types of Friction
1. Static Friction2. Sliding Friction3. Rolling Friction4. Fluid Friction
FrictionYour skateboard slows down because of friction.Friction opposes motion between two surfaces that are touching each other. The amount on two surfaces depends ontwo things:
1. Kind of surface2. Amount of force(s) pressing the surfaces together
FrictionStatic Friction – friction force that acts on objects that are not moving. It acts in direction opposite to applied force, and makes it harder to start things moving.
Types of FrictionSliding Friction – force that opposes the direction of motion of an object as it slides over a surface
Friction
Types of FrictionFluid Friction – force that opposes motion of an object
through a fluid such as water or airGases and liquids are fluids.
Skydivers experience air resistance as they fall
Static vs. Sliding Friction
Also http://www.fearofphysics.com/Friction/friction.html
Types of FrictionFor a given set of materials:
Static Friction is greater than Sliding Friction
Sliding Friction is greater than Rolling Friction
To reduce the amount of friction, apply a
LUBRICANT between the two surfaces.
Motor oil, wax, and grease are examples.
How to Reduce Friction
Other ways to reduce frictionSmooth the surfaces (polish)
Replace sliding friction with rolling friction (wheels, ball bearings)
Pick it up!
Summary of Friction
Magnitude of sliding friction depends onSurface Type (texture) andNormal Force acting on sliding object
Normal force equals weight of object (which depends on object’s mass)
Surface area does not have significant effect on sliding friction
For a given set of materials (and not counting fluid friction), rolling friction is the least friction
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