The short answer is that you do actually weigh less at the equator than you do stood at the North Pole. This is the same for the South Pole too. But this answer will debunk some of the mystery surrounding the answer and delve deeper into why this is the case.
Does your body change when you are stood at these different points?
No, your body does not change, and neither does the weight of your body. It is actually gravity that alters when you are standing at different points on the earth’s surface.
There is an alteration in gravity and other forces as you make your way to either of the Poles. These changes will return to ‘normal’ when you make your way back to where you originally were in the world.
This means you shouldn’t rely on travelling back and forth from the equator to the North Pole as some sort of excessive weight loss regime.
How does our weight stay the same but then change?
There is a combination of things that culminate to decide your weight. There are both long-scale and short-term forces that act on your body at all times.
Yes, gravity is the strongest of these forces in this instance, but there are definitely others that affect it. We are not simply being pulled down to earth by gravity.
Here are the four dominant forces and factors that will give this feeling of being ‘pulled down’ and also affect your weight.
- The earth’s gravity (this one is the obvious one and the strongest).
- The sun’s gravity (this has an effect on our bodies, not just on earth).
- The moon’s gravity (this does not just affect the ocean tides on earth!)
- The centrifugal force of earth.
Does anything else affect it?
Aside from these four main factors, the earth’s Coriolis force also plays a large role is the shape of hurricanes and currents. This does not contribute to your overall weight because it is not a static force and is constantly changing.
There are also instances where different forces will affect you when you are doing different things. For example, when you are on a swing, your weight will differ due to things like G-force and the effects of that on your body. But again, these are not constant so will not have an overall effect on your weight.
But forces like the electromagnetic force and the nuclear forces (both the strong and the weak one) are too weak to affect your weight in any significant way.
Back to the equator and the Poles
Since this answer is focusing on the difference in your weight from the equator to the North Pole, that is where we will go next. Starting with the sun and then back to earth’s forces.
The effect of the sun
The sun’s gravity is strong enough to keep the earth in orbit. Not only is that the case, but the sun’s position in relation to the earth’s Poles and equator is changing all the time, since the earth is tilted on an axis and also orbits the sun.
The result of this is that, over a few days, the gravitational force that comes from the sun and reaches a spot on the equator is the same as the gravitational force that reaches the Poles.
This means that the sun has no effect on your weight changing at the Poles versus the equator.
The effect of the moon
Similar to the effect of the sun, the moon’s gravitational pull will be equal at the Poles and the equator over the space of a few days since it orbits earth. This means that the gravitational influence from the moon also does not affect the change in your weight from the equator to the Poles.
The effect of earth’s forces
This leaves the forces on earth. We are taught that gravity is even across all of earth, but this is only an approximation. This would be the case if the earth was perfectly spherical, but it is not.
The fact that the earth is spinning on its own axis means that the shaped of it is slightly flattening, meaning it is not spherical. The shape is called an oblate spheroid. interestingly, if you stand at the equator at sea level, you are 6378 km away from the center of the earth.
But I you stand at sea level on either of the Poles, you will be 6357 km away from the center of the earth. This is down to the slightly flattening of earth.
How does this affect gravity?
Since gravity’s effects will weaken when you are further away from the body that is exerting gravitational force, this means that gravity is weaker at the equator.
This is because these points are further from the center of mass of earth. We are obviously assuming that earth’s center of mass is the center of the earth. But this can be complicated as there are irregularities on the surface of earth like mountains and other large weigh fluctuations.
But it is near the center.
What about centrifugal force?
The earth’s centrifugal force will also affect this. This varies with latitude just like gravity. centrifugal force is an outward force that you feel when you are in something called a rotating reference frame.
Centrifugal force is not a fundamental force like gravity, but it is a very real feeling in the body. The equator has more centrifugal force than the Poles since it is spinning more than the Poles. The Poles are not spinning at all so have no centrifugal force.
If the earth was not spinning and there was no centrifugal force, we would feel the effects of gravity more strongly. The centrifugal force on your body at the equator is 0.034 m/s2 times the mass of your body. And at the Poles it is 0.
So, back to the original question
If we take into account all of the points we have made in this answer, your total mass when at sea level at the equator will be 9.764 m/s2 times you mass.
At the Poles it is 9.863 m/s2. These numbers would of course be different if we took the continents into account as well as the irregularities in mass on the surface of earth. But you will weigh around 1% less at the equator than you do at either of the Poles.
If we make this easier to understand or put into perspective: if you weigh 200 pounds when you are standing at the North Pole, then you will weigh 198 pounds when you stand at the equator.
Interestingly, this does not just apply to the Poles and the equator. We have treated them as a definitive binary, but this is not the case. You will way a slightly different number at different parts of the world depending on the latitude of that place.
Think of this effect as a sliding scale between the two Poles and the equator as opposed to two definitive extremes. The closer to the equator you are, the less you will weight thanks to the effects of gravity and the earth’s centrifugal force.