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On this page, you will find out the difference between mass and weight. I think that one good way to understand this is to work it out for yourself using the following examples.

You stand on a pair of bathroom scales. You look at your weight - 55 kg. Oops, wrong! this is your mass. Your weight is actually 550 Newtons.

Question - what is the mathematical link between the two figures?

Click on the apple to reveal the answer and a little more information.

Imagine you are off to the planet Mars for a holiday. The trip is quite long so you go for a wander round the space liner. Since you are a long way from the Earth, there is no gravity (well actually there is, but it is so small that there is no way that you could feel it). You are held to the deck of the space liner by velcro slippers. Rather nice actually, large fluffy animal style! You go into a room which is labelled massometer and the wall display says 55kg. You get bored with this after about 3 seconds and do a little more wandering. You play a couple of video arcade games and have lunch. You head back to your seat but notice a room labelled 'I speak your weight'. You go in to investigate. In the middle is a pair of bathroom scales, covered in velcro. You step on them and the machine speaks in a rather metallic tone of voice:

"Your weight is zero"

"But it can't be, I weigh 550 Newtons on Earth"

you reply. The machine is linked to the rather clever ship's computer and you nearly jump out of your skin when it answers:

"Oh yes it is, I do not tell lies!"

So you rush back to your seat and forget about it because the video is really good. When the space liner lands on Mars, you have to wait for an hour or so before you can get off. You head back to the two rooms you visited earlier. In the 'massometer' room, you find that your mass is 55kg (again). In the 'I speak your weight' room, the computer tells you that:

"Your weight is 208.5 Newtons"

Hmmm, you think to yourself, Now that we are on Mars, some of my weight seems to have come back. You wander off to get some food.

So, What is going on? Think about your mass on Earth, on the space liner and on Mars. What do you notice? So does mass change?

Now consider your weight. Where did you have weight and where were you weightless? So, what causes weight?

Click on the apple to check your answers to these questions.