Why did friction make it difficult to discover newtons first law of motion

Friction made it difficult because an object in motion may not always stay in motion due to the friction caused by its movement. For instance, if you roll a ball down a straight platform, it will not go on forever. The friction of the platform and the ball with eventually slow it down and stop it.

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Because Static Friction and Inertia can be confused, because mass defines how much inertia a body has, that is, the difficulty of putting some acceleration in it. And it's basically the same with friction. Static friction says that, for example, for you to pull a table with your hands, you need to put force (obviously), as measured by Newtons. From the Newton that the table start to accelerate, then there is the static friction.

For example:

To speed up the table, you put five Newtons, and the table does not move. Put ten, still not moving. It puts 11, and it begins to move (accelerate). So the static friction force is 10 Newtons.