Force, Friction and Sound
Category : 8th Class
Force, Friction and Sound
Force
A force is a push or pull upon an object resulting from the object's interaction with another object. Whenever there is an interaction between two objects, there is a force acting each of the objects.
Force acting between objects can be placed into two categories:
Contact Forces
Are those types of forces which result when the two interacting objects are perceived to be physically contacting each other.
Types of Contact Forces
Non-contact Forces
Are those forces which result when the two interacting objects are not in physical contact with each other.
Types of Non-contact Forces
Pressure
Pressure, in mechanics is the force per unit area exerted by a liquid or gas on a body surface, with the force acting at right angles to the surface uniformly in all directions.
Mathematically: \[p=\frac{F}{A}\]
Where P is the pressure, F is the normal force and A is the area. Unit of pressure is Pascal or\[N/{{m}^{2}}\].
Atmospheric Pressure
The pressure exerted by the atmosphere is called atmospheric pressure. It decrease with increase in height.
Friction
Friction is the force that opposes the motion of an object when the object is in contact with another object or surface. Friction results from two surfaces rubbing against each other or moving relative to one another. It can hinder the motion of an object or prevent an object from moving at all. The strength of frictional force depends on the nature of the surfaces that are in contact and the force pushing them together.
Causes of Friction
Friction occurs because rough surfaces tend to catch on one another as they slide past each other. Even surfaces that are apparently smooth can be rough at the microscopic level. They have many ridges and grooves. The ridges of each surface can get stuck in the grooves of the other, effectively creating a type of mechanical bond or glue, between the surfaces.
Kinds of Friction
Friction is a Necessary Evil
Friction plays an important role in our daily life but it has also some harmful effects. For example, friction enables us to walk on the floor, to write on a paper, to stop a moving
Object, etc. It also has some disadvantages. For example, friction wears away the soles of our shoes, tyres of vehicles, rubbing machine parts and brake pads of vehicles, etc.
Sound
Sound is a physical phenomenon that stimulates the sense of hearing. Sound is produced by vibrating objects. In humans, hearing range of frequencies is from 20 hertz to about 20,000 hertz. Hertz (Hz) is the unit of frequency which is equal to number of vibration or cycle per second. The speed of sound in air is about 340 m/s. Sounds of frequencies above the range of normal human hearing, higher than about 20,000 Hz, are called ultrasonic. Sounds below 20 Hz are called infrasonic.
A sound wave is a longitudinal wave as the individual air molecules that carry the sound move back and forth, parallel to the direction of wave motion. Thus, a sound wave is a series of alternate increases and decreases of air pressure.
The frequency of a sound wave is a measure of the number of waves passing a given point in one second. The distance between two successive crests of the wave is called the wavelength.
Characteristics of Sound Wave
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