The Universal Gravitational Law states that F=(G)(m1)(m2)/d^2, because of this we know that force is proportional to 1/distance squared. In other words, a short distance has a strong force and a long distance has a weak force.
Let's think about this in relationship to the Earth. The side of the Earth closer to the Moon experiences the Moon's gravitational force more than the side that is farther away from the Moon. The net force acting on each side of the Earth is what causes the tides. Say that the on the side closer to the Moon, the Moon's gravitational force exerts 150N and on the other side, only 50N. (note: these numbers are grossly exaggerated just to detail the concept) Additionally, the gravitational force from the center of the Earth is 100N. To find the net force on each side, the Earth's gravitational force is subtracted from the moon's force on each side. Therefore, the net force on the close side is 50N and the net force on the far side is -50N. The positive force indicates that the close side is being pulled toward the Moon and the negative force indicates that the far side is being pulled away from the moon. It is this imbalance that causes the tides. If the forces weren't opposite, tides wouldn't exist. Also, if tides were determined by gravitational pull instead of the relationship between force and distance, tides would be caused by the Sun, not the Moon.
This video explains tides really well:
In each day, there are two high tides and two low tides due to planetary revolution. Six hours pass between each high tide and each low tide, also meaning that from high tide to high tide is 12 hours and between low tide to low tide is 12 hours.
Niara, I really enjoyed reading your blog post! Your video was the most helpful learning tool that I found while reading your blog. When I was looking for tide videos to post on my blog, they all consisted of diagrams and images for the entire duration of the video. I found it really beneficial that in your video, there was an actual person talking to me and I could see his face and body movements. This blog post made me want to know more about the earth's tides and attempt sample problems to do with the Universal Gravitational Law in order to fully understand this topic.
ReplyDeleteThanks!