Mechanical waves are influenced by the medium’s properties because they rely on the medium’s particles for propagation. Factors such as the density, elasticity, and temperature of the medium affect the speed and behaviour of the wave. For instance, in solids, where particles are closely packed and interactions are strong, mechanical waves, like sound, travel faster compared to gases. The elasticity of the medium, which refers to its ability to return to its original shape after being disturbed, also plays a crucial role, affecting the wave’s speed and energy transfer efficiency.

The constant speed of electromagnetic waves in a vacuum is a fundamental property derived from Maxwell’s equations. These equations describe the behaviour of electric and magnetic fields and their interactions. The speed is denoted by 'c', approximately equal to 3x10^8 m/s. This constancy arises because, in a vacuum, electromagnetic waves are unaffected by a medium's properties. Their speed is a result of the permittivity and permeability of free space, intrinsic properties that dictate the behaviour of electric and magnetic fields, respectively, leading to a fixed, constant speed for all electromagnetic waves in a vacuum.

Yes, electromagnetic waves can be polarised. Polarisation refers to the orientation of the oscillations of the wave. For electromagnetic waves, it involves confining the oscillations of the electric field to a single plane. This is possible because electromagnetic waves consist of perpendicular electric and magnetic fields. Mechanical waves, particularly transverse mechanical waves, can also be polarised. However, this involves confining the oscillation of the medium's particles to a single plane. The primary difference stems from the nature of oscillations: electric and magnetic fields for electromagnetic waves, and particles of the medium for mechanical waves.

Electromagnetic waves can travel through both a vacuum and materials, their propagation is facilitated by the oscillation of electric and magnetic fields. When travelling through materials, the waves interact with the atoms or molecules of the material. This interaction can lead to reflection, absorption, or transmission of the waves, depending on the material's properties. The speed of electromagnetic waves is also influenced; it slows down when passing through a material compared to a vacuum. However, the fundamental mechanism of energy transfer, via the oscillating electric and magnetic fields, remains constant regardless of the medium.

Mechanical waves, such as sound, cannot propagate in space because it is a vacuum. They rely on a medium, like air, water, or a solid substance, to transfer energy. In the vacuum of space, there are no particles to carry the wave, thus no sound or any form of mechanical wave can travel. Energy transmission in mechanical waves is facilitated by the oscillation of particles within the medium; each particle passes energy to its adjacent particle, propagating the wave. In the absence of a medium, there are no particles to oscillate, making the propagation of mechanical waves impossible.