FRICTION: The force that one surface exerts on another when the two surfaces rub against each other.
Friction depends on… Roughness of surfaces and Force that objects are being pressed one against the other; or their weights
What Causes Friction? Even though a surface may look smooth, if you magnify the surface it isn’t smooth. 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 they stick together.
There are four different types of friction
Sliding friction Sliding friction: Friction that occurs when one solid surface slides over another. EXAMPLES Ice skating A sled down a hill Skiing down a hill
Sliding friction The sliding friction is between the skies and the snow. The friction creates heat and the heat melts the snow and now the skies slide over the snow.
Rolling friction Rolling friction: Friction that occurs when an object rolls over a surface. Ex: Rollerblading A soccer ball on the ground
Rolling fiction When the soccer players dribbles the ball the ball over the ground and it creates rolling friction.
Fluid friction Fluid friction: Friction that occurs as an object moves through a fluid. Examples: Water skiing Water tubing Swimming through the water
Fluid friction When the boat goes over the water it creates the fluid friction.
Static friction Friction that acts on something that is not moving Piano is held in place by static friction Static friction keeps you in your seat No heat or wear is generated
Static friction In this picture the world cup trophy is sitting on the table and there is static friction going on.
Mu (µ) µ: It is scale that determines how much friction is being exerted. With lots of friction it is high µ. With little friction it is low µ.
Mu (µ) When the car is burning out between the wheel and the road there is high µ. When the kid spreads the butter on the corn it is low µ.
Coefficient of friction
Friction angle Block at rest on plane with angle α : fn = mg cosα ft = mg sin α At rest |ft|≤µfn. Maximum α : ft = µfn Substituting, mg sin α = µmg cos α α = tan-¹ µ Sometimes called the friction angle or the angle of repose.
Angle of repose The angle of repose or, more precisely, the critical angle of repose, is the steepest angle of descent or dip of the slope relative to the horizontal plane when material on the slope face is on the verge of sliding. This angle is given by the number (0°–90°).
Advantages and Disadvantages of Friction Advantages Friction enables belts to cling to pulleys and nails to hold objects together.
A running car or bicycle uses friction to stop. As the driver steps on the brakes, the vehicle slows down to a full stop. This is possible because of the friction between the brakes and the wheels.
Walking, running, playing, writing, sitting, standing, or eating cannot be possible without friction.
Disadvantages of Friction
Shoes, slippers, tires and anything that are used for moving become worn out. Friction produces heat that causes objects to wear out.
Friction makes work tedious. Because of the resistance, workers need to exert more effort and energy to accomplish their work to overcome resistance.
Some machines perform less efficiently and wear out faster with friction.
Friction also causes sparks, overheating, and machine breakdown.
Friction reduces speed. Even airplanes cannot fly as fast as they are able because of air friction.
Racing cars and other vehicles consume more energy to run fast and overcome the resistance of the roads.
Ways of reducing friction
Smoothing out Surface
ex. Applying floor wax and scrubbing the floor.
Placing a slippery substances between two solid surfaces
ex. Grease, oil and other lubricating liquids
Using rotating objects
ex. Roller bearings, ball bearings and wheels
Ways to increase friction
New materials with more bumps and hollows are produce for making car brakes lining.
New styles for the soles of athletes’ shoes. Its aim is for runners to run with greater speed.