6.2 Friction What is friction? What is friction? Friction acts on an object which slides or tends to slide over another object. e.g. The car cannot travel without friction. What is the effect of friction on our lives?
6.2 Friction
What is friction?What is friction? Friction acts on an object which slides
or tends to slide over another object.
e.g. The car cannot travel without friction.
What is the effect of friction on our lives?
6.2 Friction
How can we measure the friction between a sliding
block and a table?
Pull the block with a spring balance
6.2 Friction
When the pulling force is small,pulling force = frictionThe block does not move.
pulling force
friction
6.2 Friction
Increase the pulling force such that
pulling forcemaximum friction between the block and the table=
The block still does not move.
pulling force
friction
6.2 Friction
pulling force
friction
Increase the pulling force such thatpulling force
maximum friction between the block and the table>
The block moves.Simulation: Friction
6.2 Friction
Friction depends on the nature of the sliding surfaces.
Rubber is used in tyres and brake pad on a bicycle
tyre
brake pad
It can exert a large friction.
6.2 Friction
Special carved patterns help to increase friction.
The grooved pattern underneath a hiking shoe
6.2 Friction
Rolling motion in ball bearings
Reducing frictionReducing friction
Lubricants used in bicycle gears
Can you give daily examples of reducing
friction?
6.2 Friction
A levitated object experiences negligible friction during motion.
An ‘air cushion ball’ game A Maglev
6.2 Friction
Fluid frictionFluid friction Fluid friction – resistive force exerted on
a body moving in a gas or a liquid.
e.g. air resistance, water resistance
speed of the object fluid friction
Can you give daily examples of reducing
fluid friction?
6.2 Friction
Airplanes are in streamlined shapes to minimize air resistance.
Swimmer wear smooth suit to reduce water resistance.
6.2 Friction
weight
Terminal velocityTerminal velocityWhen a skydiver just jumps out of an aircraft …
velocity = 0 force acting on him:
weight net force = weight acceleration = g
(downwards)
EXTENSION
6.2 Friction
When he moves faster...
weight
air resistance force acting on him:weight
( , < weight)
net force = weight – air resistance acceleration
( )
velocity
(constant)air resistance
6.2 Friction
air resistance = weight
Air resistance continues to increase such that
weight
air resistance
acceleration = 0 he moves at a
constant velocity
= weight – air resistance= 0
Terminal velocity
net force
Simulation: Skydiver
6.2 Friction
Terminal velocity depends on the(1) weight of the falling object
heavy objectlarge gravitational force
large terminal velocity
object with large surface area
large air resistance
small terminal velocity
(2) surface area of the falling object.
6.2 Friction
A parachute has a large surface area
Why can a parachute make the skydiver land
safely?
Terminal velocity of the skydiver
6.2 Friction
That’s the end of Section 6.2
Check Point
Key Ideas
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