Author: Hannah Richards
Our very own Professor Paul Nightingale gave UKIP MP Douglas Carswell a quick science lesson after he criticised his Brexit analogy on Twitter. Nightingale, in support of free-trade links closer to home cleverly compared the situation using the concept of gravity.
He tweeted: ‘Want to understand trade? Think gravity: size and distance matter. UK-Ireland greater than UK-China. Jupiter is big but the moon moves tides’. His planetary comparison was soon met with backlash from Douglas Carswell who responded: ‘Actually it’s the gravitational pull of the sun. The moon’s gravity does Spring / neap tides’.
Clearly Carswell was unhappy with Nightingale’s comparison, prompting his bold decision to argue with a science academic. Nightingale took no time in setting him straight: that although the sun is larger it’s the distance that matters and therefore the moon causes the tides. Carswell, unphased by Nightingale’s reply, exclaimed his surprise that an academic opposed his claim.
The argument went back and forth, others joined in and Carswell didn’t budge. Nightingale’s final tweet silenced the argument, he provided a link to 1467 examples of evidence in 103 published academic papers that prove the moon causes the tide. Nobody could argue with that mountain of evidence. Carswell later deleted his tweet – he was probably a tad embarrassed.
As most people are aware (with a previously noted exception) the moon’s gravitational pull causes daily tides. Despite the moon’s mass being drastically smaller than that of the earth, the moon’s gravity pulls on different parts of the earth as it rotates, simply because it is so close to us. The gravitational pull of the moon noticeably moves water causing oceans to bulge towards the moon. Interestingly, the ocean on the side of the earth not facing the moon also bulges, therefore gravity is not the only force causing tides.
Inertia is also an important player. Inertia is matter’s tendency to resist changes in their state of motion – objects tend to keep doing what they are doing until they meet another force. So whilst the water that is nearest the moon is being influenced by gravity the water furthest from the moon stays put. Both sides experience both forces, but on the side closest to the moon the gravitational force is greater and on the face opposite the moon inertia is at its greatest. The bulges on either side remain as the earth rotates explaining why there are two high tides and two low tides throughout the duration of the day.
Lastly (so Douglas Carswell doesn’t feel completely stupid) the sun does have some impact on the tides. When the sun’s gravitational pull lines up with the moon’s gravitational pull both gravitational pulls are combined, leading to more extreme high and low tides.