Notes

things to revise from the book:
1.electrostatic force
2.frictional force
3.magnetic force
4. balanced and unbalanced forces

Important
pressure is the force exerted per unit area.
1 PA= 1 NEWTON/1 METER SQUARE
It is directly proportional to force.
t is inversely proportional to area.
Fluids are those that can flow. For example: Liquids including water and gases including air.

Properties of Fluid Pressure
-Pressure increases with an increase in depth.
-Pressure decreases with height.
-Pressure applied at any point is equally transmitted in all directions.

Friction: -
It is a type of force that opposes the relative motion between two surfaces of objects in contact.
Friction exists between two surfaces due to irregularities on the surfaces of the object in contact, interlocking of micro-level irregularities of the two surfaces and ploughing of harder surfaces into smoother surfaces.

Factors that affect friction: -
Nature of the two surfaces in contact (Roughness or smoothness of the surfaces).
Force (weight) pressing the two surfaces together.

rolling<sliding<static
Static Friction: -
The force of friction that comes into play when the object is at rest is known as static friction.
Sliding/Kinetic Friction: -
The friction that comes into play when objects are in motion is called as sliding/kinetic friction.
Rolling Friction: -
When one body rolls over the surface of another body, the resistance to its motion is called the rolling friction.

Drag/Fluid friction depends on the: -
nature of the fluid
shape of the object (area of contact)
speed of the object
Friction – A Necessity: -
Friction is responsible for writing, walking and transmitting energy.
Friction is responsible for starting or stopping.
Friction is used in gripping or holding an object with our hands.

Friction – An Evil or Nuisance: -
Friction is responsible for wear and tear of various parts of machines.
Friction decreases the efficiency of machines as a part of the machine’s energy is lost in extra friction.
Friction can be reduced by using:
grease, oil, powder, ball bearing, and cushion of dry air between the moving surfaces.
using anti-friction alloys.

friction can be increased by making a surface rough, e.g.: -
The Tyres and shoes have treads and grooves to improve their grip on road.
Sports shoes have spikes/cleats on their soles to get a better grip on the ground.
Gymnasts apply some coarse substance/chalk powder on their hands for a better grip on uneven bars.
Kabaddi players rub their hands with soil for having a better grip on their opponents.


Metals are:
hard to touch.
lustrous i.e., freshly Cut surfaces of metals have characteristic shining.
malleable; the property of metals by which they can be beaten into thin sheets is called malleability.
ductile; the property of metal by which it can be drawn into wires is called ductility.
sonorous i.e., metals produce ringing sound when struck on a hard surface.
Good conductors of heat and electricity.
Physical Properties of Non-metals:

Non-metals are soft and dull (e.g., coal and Sulphur).
Non-metals are generally brittle, i.e., they break down into a powdery mass on tapping with a hammer.
They are not sonorous.
They are poor conductors of heat and electricity.
Displacement Reaction: More reactive metals displace less reactive metals from their metal compounds in aqueous solutions.
metalloids: Elements which possess characters of both metals and non-metals are called metalloids.

Human ear
Outer ear = pinna: collects sound from the surroundings.
Sound passes through a tube called an auditory canal.
Eardrum (tympanic membrane) → vibrates when the sound incident.
Vibrations are sent to the inner ear, from there it goes to the brain as signals via the auditory nerve.Human ear
Outer ear = pinna: collects sound from the surroundings.
Sound passes through a tube called an auditory canal.
Eardrum (tympanic membrane) → vibrates when the sound incident.
Vibrations are sent to the inner ear, from there it goes to the brain as signals via the auditory nerve.

The number of oscillations per second is called frequency. Expressed in Hertz (Hz).
Time taken for one complete oscillation to travel across a point. T = 1/f. (Seconds)
Below 20 Hz (inaudible) → infrasonic range
Above 20 kHz (inaudible) → Ultrasonic range