Solar vs Lunar Tides: Explaining the Difference

In summary: If you call the radius of the Earth ε, then you can see that the gravitation of the sun actually applies to points on Earth over a distance which varies from r-ε for the nearest point, to r+ε for the furthest point. It's this difference in gravity due to the difference in distance that generates the tides.Now if you recompute the gravity difference between near and far points, you will see why the lunar tide is so large (hint: it has to do with the ratio ε/r).Found this website which explains it in more detail:http://oceanworld.tamu.edu/resources/ocng_textbook/chapter17/
  • #1
The Head
144
2
I have a question about the effects of solar and lunar tides. I know that the effect of lunar tides is twice that of solar. However when I calculated the force of gravity of the Sun on the EArth vs the Moon on Earth using F=GmM/r^2 the force due to the Sun was much greater. Can anyone help me explain this? Thank you!
 
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  • #2
The Head said:
I have a question about the effects of solar and lunar tides. I know that the effect of lunar tides is twice that of solar. However when I calculated the force of gravity of the Sun on the EArth vs the Moon on Earth using F=GmM/r^2 the force due to the Sun was much greater. Can anyone help me explain this? Thank you!

If you call the radius of the Earth ε, then you can see that the gravitation of the sun actually applies to points on Earth over a distance which varies from r-ε for the nearest point, to r+ε for the furthest point. It's this difference in gravity due to the difference in distance that generates the tides.

Now if you recompute the gravity difference between near and far points, you will see why the lunar tide is so large (hint: it has to do with the ratio ε/r).
 
  • #3
Found this
http://oceanworld.tamu.edu/resources/ocng_textbook/chapter17/chapter17_04.htm"

Check out equations (17.12), (17.13), & (17.14)
 
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  • #4
You're kidding me. You linked to a website that promotes a crackpot theory? Please don't tell me you believe that nonsense.

The tide raising force is indeed inversely proportional to the cube of the distance between the bodies.

Looking more closely at the link I agree it was an inappropriate reference as it is about something else entirely, so my apologies.

However I am suprised that no one has come into describe the mechanics of how the inverse cube relationship occurs so I will do that when I have time- It really is quite simple in principle. As oliversmsun says it is because the force due to gravitational attraction is not directly the tide raising force (TRF). The TRF stems from the difference between the forces of gravitational attraction and the forces due to the earth-moon or earth-sun mechanical systems revolving about their respective centres of mass.

Edit, thank you Gannet you posted whilst I was writing the above.
 
  • #5


Thank you for your question about the effects of solar and lunar tides. It is true that the effect of lunar tides is about twice that of solar tides. This is because the Moon is much closer to the Earth than the Sun, and the force of gravity decreases with distance. However, when calculating the force of gravity using the equation F=GmM/r^2, it is important to also consider the masses of the bodies involved.

The mass of the Sun is much larger than the mass of the Moon, so even though the Sun is further away, its gravitational force on the Earth is still greater. This is why the force due to the Sun was much greater in your calculation. Additionally, the Sun and Moon have different orbital patterns and gravitational interactions with the Earth, which can also affect the strength and timing of tides.

In summary, the Moon's proximity to the Earth and the Sun's larger mass both contribute to the difference in the strength of their tidal forces. Other factors such as orbital patterns and gravitational interactions also play a role in the complexities of tides. I hope this helps to explain the difference between solar and lunar tides.
 

1. What causes tides on Earth?

Tides on Earth are primarily caused by the gravitational pull of the moon and the sun. The moon's gravitational pull is stronger, which is why it has a greater impact on tides. The position of the moon and sun in relation to Earth also plays a role in the intensity of tides.

2. How do solar and lunar tides differ?

Solar tides are caused by the gravitational pull of the sun, while lunar tides are caused by the gravitational pull of the moon. The sun's pull on Earth is weaker than the moon's, so solar tides are typically less intense than lunar tides.

3. When do solar and lunar tides occur?

Solar tides occur when the sun and moon are aligned with Earth, creating a combined gravitational pull that results in higher than normal tides. Lunar tides occur when the moon is either full or new, and its gravitational pull is at its strongest, resulting in higher than normal tides.

4. Do solar and lunar tides affect all bodies of water the same way?

No, the intensity of tides can vary depending on the location and shape of the body of water. For example, tides in narrow, shallow bays may be more extreme than those in open oceans.

5. Can solar and lunar tides be predicted?

Yes, tides can be predicted using mathematical models that take into account the positions of the sun and moon, as well as factors like the Earth's rotation and the shape of the coastline. This allows for accurate tide predictions for specific locations and dates.

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