Friction
Uploaded by
fenway100gaming0Friction
Uploaded by
fenway100gaming0Friction
By Aahna, Falak, Feby, Kezia and Nayab
Learning Objectives
Explain the differences between static, kinetic, and rolling
1
friction using appropriate examples.
Apply the formulas for static and kinetic friction to solve
2 problems involving forces on horizontal and inclined
planes.
Friction
Friction is a contact force that opposes the relative motion or tendency
of motion between two surfaces in contact. It acts parallel to the
surface and prevents motion when a force is applied. Friction is what
keeps an object at rest even when a small force is applied, and only
when this force exceeds a certain limit does the object begin to move.
Static Friction
● Static friction is the force that resists the initiation of motion between two
surfaces in contact. It acts when the object is at rest.
● Exists only when there is a tendency to move, but no actual motion.
● Static friction prevents motion.
● Maximum static friction is given by
Kinetic Friction
● Kinetic (or sliding) friction is the force that opposes the relative motion
between two surfaces that are already sliding over each other.
● Acts when the object is in motion.
● It always opposes the direction of motion.
● Maximum kinetic friction is given by
Motion of body
Case 1:
When applied force is greater than kinetic friction.
F(a) > F(k)
[F(a) - F(k)] = ma
Case 2:
When applied force is equal to kinetic friction. (Uniform motion)
F(a) = F(k)
F(a) - F(k) = 0 = a
Motion of body
Case 3:
When applied force is zero. (Body remains at rest)
F(a) = 0
[F(a) - F(k)] = -F(k)
Rolling friction
● Rolling friction is the resistance experienced when a body rolls over a
surface.
● It is due to temporary deformations of the surfaces in contact.
● Value is much smaller than both static and kinetic friction
● Rolling contact involves a finite contact area, not a perfect point.
● A force is still required to keep a rolling object in motion.
Advantages & Disadvantages
Advantages: (Kinetic & Static)
A. Walking, break of vehicles etc
B. Prevents slipping
Advantages: (Rolling)
A. Enables easier movement of heavier objects.
B. Makes wheeled transport and machines efficient
Disadvantages:
A. Causes wear and tear
B. Leads to energy loss as heat
Ways to reduce friction
Static & Kinetic Friction:
A. Lubricants
Rolling Friction:
A. Ball bearings
B. Air cushion
Simulation
https://phet.colorado.edu/sims/html/forces-a
nd-motion-basics/latest/forces-and-motion-b
asics_all.html
Problems
related to the
topic:
1. A box is placed on the floor of a train. If the coefficient of static
friction is 0.2, what is the maximum acceleration the train can have
without the box slipping?
2. A 10 kg box lies on a horizontal floor. What is the maximum
horizontal force that can be applied to it without causing motion,
if μs=0.4?
3. A 12 kg block slides on a floor. If the coefficient of kinetic friction is
μₖ = 0.3, what is the frictional force acting on it?
Thanks!
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