To sum up – if we're talking about the objects on the Earth's surface, all we need to do is to divide the weight in newtons by 9.81 (or 10 if we only need a rough estimation) to obtain the mass in kilograms. One newton is the force equal to the weight of an average apple with a mass of 102 g.Īn object with a mass of one kilogram, e.g., 1 kg of sugar will weigh ~9.81 newtons on the surface of the Earth.Īgain, in Earth gravity, 1 kN = 102 kg = 225 lbs.ġ-ton car will weigh 10 kN on the Earth's surface. We know that average gravity on Earth is equal to approximately g = 9.81 m/s², so if we're on Earth: Have a look at our explanatory table, and all should be clear! The weight is then expressed in force units – newtons. However, physicists will call that quantity mass, and the weight word is reserved for the amount of force acting on the object, either due to gravity or to a reaction force that holds it in place. In everyday life, we use the weight term to express the concept of quantity – the amount of 'matter' in an object, and we express it in, e.g., kilograms or pounds. But first of all, we need to explain that mass and weight mean something different in common usage and the physics world. To have a grasp of that unit and understand how much one newton is, let's have a look at some examples. m – Mass of the object receiving the force and.You can define it from Newton's second law of motion, which states that:į = m × a, so the newton is 1 N = 1 kg × 1 m/s², The unit was named after Sir Isaac Newton and was standardized and widely accepted in 1950. And we stuck with it.The newton is a basic SI unit of force, which is equal to the force needed to accelerate one kilogram of mass at the rate of one meter per second squared in the direction of the applied force: The original sense was of motion, which led to that of lifting, then to that of 'measure the weight of.' The older sense of 'lift, carry' survives in the nautical phrase weigh anchor.īefore Newton, the concept of inertia didn't exist so the distinction between mass and weight made no sense when the word was first introduced. So why don't we call it 'mass'? Well, according to, 'weight' is a very old word, The only time we care about weight is when we're about to snap the cables in the elevator (too much sweetened coffee?) or have some other engineering task where we care about the actual force of gravity (as opposed to the quantity of material). We use the kilogram because it is a more useful metric in 'daily life'. Well - with Blue Mountain I might not need sugar but that's another story.

You can now express relative weights as a ratio to the reference.Īll I need to do when I move to Jamaica (would that I could…) is recalibrate my scales - and my coffee will taste just as sweet as before. So if I have a 1 kg calibration weight, it might read 9.81 N in one place, and 9.78 N in another place but if I put the reference weight on the scales and then say 'if you feel this force, call it 1 kg' - that is what I get.

If I calibrate scales using a reference weight, they will indicate (at that location) the amount of mass present in a sample relative to the calibration (reference). When you are interested in 'how much' of something there is - say, a bag of sugar - you really don't care about the local force of gravity on the bag: you want to know how many cups of coffee you can sweeten with it. This is in part caused by the rotation of the earth, and in part by the fact that the earth's surface is not (quite) a sphere. The problem is that while mass is the same everywhere on earth, weight is not - it can vary as much as 0.7% from the North Pole (heavy) to the mountains of Peru (light).

Newton units in kg