If we throw a rock to a pond, is the resulting wave tranversal or longitudinal?

Using my logic it is a tranversal wave because the particle of water moves/vibrates up and down while the wave travels outward. (In my understanding a tranversal wave is defined as a wave where the particle of the medium vibrates perpendicular relative to the wave's motion)

But a book (by D.C. Giancoli) says that "In a fluid, only longitudinal waves can propagate; this is because any tranverse motion would experience no restoring force since a fluid can flow."

If he is correct, can anyone convince/prove to me that the wave in the top question is a longitudinal wave? Also can anyone explain more about "any tranverse motion (in a fluid) would experience no restoring force since a fluid can flow"?

Thanks for all...

Waves <b>inside</b> a fluid must be longitudinal. Waves <b>on the surface</b> of a fluid can be transverse.

On the surface of a pond transverse waves can exist because gravity provides a restoring force.

If the oscillation occurs along the axis of the wave propagation, it is a longitudinal wave. If oscillation occurs perpendicular to the direction of the wave propagation, it is a transversal wave.

Thanks... Some other questions though...

"The velocity of a wave depends on the properties of the medium in which it travels. The relationship (on a string) is...

v=sqrt(Ft x l / m)
or
v=sqrt(Ft / (m / l))

Ft: tension on string
l: string length
m: string mass
"

My book said: "we do expect the tension to be in the numerator because when tension is greater, we expect velocity to be greater since each segment of string is in better contact with its neighbour."

I'm confused here. Shouldn't a greater tension makes the atoms (?) spaced further? Shouldn't compression be the thing that makes "each segment of string in better contact with its neighbour"?

Also is the equation (related to vibration) below relevant when we are talking about waves?

T = 2 x pi x sqrt(m/k)

Thanks a lot!!!

The book's explanation sounds a it funny to me.

A greater tension in the string means that the restoring force between the atoms (which tends to pull the string back to its rest position) is greater. That makes the waves move faster.

The last equation you mentioned is a simple harmonic motion expression for the period of oscillation of a mass on a spring. It is not directly relevant to waves on a string, unless you look at segments of the string as being similar to masses on springs (which is possible).

[quote]
Waves inside a fluid must be longitudinal. Waves on the surface of a fluid can be transverse.

On the surface of a pond transverse waves can exist because gravity provides a restoring force.
[quote]

Uhm... After thinking for a while I don't really get it yet... Don't gravity also act at the inner of the fluid?

Also if we throw a rock to a pond, why will the amplitude the smaller and smaller as the wave travels farther? Is it because of friction?

Thank you!

<i>Uhm... After thinking for a while I don't really get it yet... Don't gravity also act at the inner of the fluid?</i>

Yes, but only to establish a constant pressure gradient. If a bit of the fluid moves up or down, it stays where it has moved. If it's on the surface and it moves up, gravity pulls it back down.

<i>Also if we throw a rock to a pond, why will the amplitude the smaller and smaller as the wave travels farther? Is it because of friction?</i>

Partly. Mostly it's because the energy of the wave is spread out over a larger and larger area as the wave moves outwards.