Which waves require a medium for transmission

Mechanical waves

Explanation:

As per the criteria of wave propagation we can divide the waves into two parts

1). Mechanical waves : Those waves which require medium to travel then it is known as mechanical waves

examples: Sound waves, String waves etc

2) Non Mechanical waves: Those waves which do not require any medium to propagate is known as non mechanical waves.

Examples : Light waves, electromagnetic waves etc

So here correct answer would be Mechanical waves

friction

explanation:

they us to move forward and backwards