Friction comes into play only when

Among different types of friction, the force that acts just before an object starts moving is known as

Once an object starts moving, the friction acting on it becomes smaller because

When a body rolls over a surface instead of sliding, the friction acting on it

Rough surfaces offer more friction because

Oil or grease is applied to machine parts mainly to

Luggage bags fitted with wheels can be moved easily because

Continuous rubbing of two surfaces not only slows motion but also produces

A car moves safely on a wet road because its tyres have deep grooves on them. These grooves help by

When a bell is struck, it produces sound only till it is vibrating. This observation shows that sound is produced due to

For sound to travel from one place to another, it always requires

Sound can travel through solids, liquids and gases but it cannot travel through

The number of vibrations made by a body in one second is known as

The SI unit used to measure frequency of sound is

A sound produced by beating a drum hard is louder because

A shrill sound differs from a dull sound mainly due to difference in

The thin stretched membrane inside the ear that vibrates when sound enters is called

Human beings can normally hear sounds having frequency between

A tuning fork is struck and then touched with a finger. The sound stops immediately. This happens because

Lightning is a natural phenomenon which is actually caused due to

When a plastic comb is rubbed with dry hair, it acquires

When two objects carrying similar charges are brought close, they

When objects carrying opposite charges are brought close, they

The simple device used to test whether an object is charged or not is

An earthquake occurs due to

The place inside the Earth where an earthquake begins is known as

The instrument that records earthquake waves on paper is called

The scale used to measure the strength of an earthquake is

During a thunderstorm, people are advised not to stand under tall trees. This is because