# Forces 01

This KS3 Science quiz asks questions on forces. It doesn't matter if something is moving or stationary, there are always forces acting on it. The famous Scientist, Isaac Newton, realised this and came up with his three laws of motion. Forces are measured in **newtons** which have the symbol **N**. One of the most famous of Newton's laws is that if an object isn't moving, the forces acting on it are equal and opposite.

Imagine a book lying down on a shelf. The book puts a downward force on the shelf. The shelf must therefore be putting exactly the same force back on the book. Now if you add a whole lot more books to the shelf, if the shelf can't push back with the same force that the pile of books is putting on the shelf, it moves - in other words, it collapses! The force a book puts on a shelf is its **weight**. Weight is therefore measured in newtons. Unfortunately, in everyday life, you will hear most people referring to weight using kilograms. This is entirely incorrect, kilograms are a measure of **mass**. Weight is the force created by the attraction of gravity on the mass of an object. On Earth, a mass of 100g (0.1kg) has a weight of about 1N.

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