No, they actually travel through the vacuum of outer space, but it also requires the absence of a material sedium.
Answer:
B. Gravitational force
Explanation:
The gravitational force of an object (also called weight) is given by

where m is the mass of the object and g is the acceleration of gravity, and it always points in the downward direction.
In this problem, the arrow labelled with 4 is the only force pointing downward: therefore, it must be the gravitational force.
The other arrows represent:
1 --> component of the gravitational force parallel to the plane
2 --> force of friction
3 --> component of the gravitational force perpendicular to the plane
The answer is letter C.Weight (on Earth) is the force due to the mass of Earth attracting whatever mass is subject of discussion.
The force of attraction between any two masses is called Newton's Law of Universal Gravitation:


is simply a given constant.
If we're at the surface of Eath,

refers to the mass of the Earth,

to the mass of whatever is on the surface of Earth, and

to the radius of Earth.
Normally, we define a constant

to be equal to

; in which

is the mass of Earth and

the radius of earth;

happens to be around 9.8.
By that, we adapt the Law of Universal Gravitation to objects on the surface of Earth, we call that force Weight.

As you can see, weight is directly proportional to mass, more mass implies more weight.
In that formula for Energy, 'F' is the frequency of the photon.
But <u>Frequency = (speed)/(wavelength)</u>, so we can write the
Energy formula as
E = h c / (wavelength) .
So the energy, in joules, of a photon with that wavelength, is . . .
E = (6.6 x 10⁻³⁴) x (3 x10⁸) / (that wavelength)
= <em>(1.989 x 10⁻²⁵) / (that wavelength, in meters) .</em>