Newton's First Law of Motion

In this post I'll try to explain to you what inertia is and how it works.
Here is the Newton's first law of motion:
"Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it."


In simple this means that:

If something is moving at a constant speed (e.g. a car going at 40mph) or even if it is stationary, it will tend to remain at that speed unless a force acts on it (e.g the friction on the ground or in the air - air resistance).


On earth we don't often see this directly as forces are constantly acting on everything such as gravity, friction and air resistance. However, if we were to imagine a car being pushed off a ramp in deep space at a set speed, for example 10mph, it would theoretically keep travelling at this speed forever until some force came into contact with it (hitting something for example).

Galileo, before Newton, also developed a law called the law of Inertia. This basically means that an object which is at rest tends to stay like that unless another force acts upon it.

This is because of friction of course. Have you ever noticed that when you try to push something heavy on the ground you need a huge force at the start, but when it gets going its much easier? You may also have noticed that as soon as you stop pushing the object quickly stops.

Friction does this because, if you can imagine, every object (even flat objects) have uneven surfaces. They have rumps and bumps all over them and friction is caused by the different bumps getting stuck between each other on two surfaces. Inertia happens because when an object is at rest the object's bumps are

nicely settled into the surface beneath it's cavities. You need a big force to get the bumps out, and then after that the object just skips over the cavities making it easier to push. Once you stop pushing the object stops once more.

An example of this is in a clock-work mouse. When you wind up the mouse and set it going it goes for a while, and sometimes it stops. If you then give it a little tap then the mouse starts going again. Know you know why.

I hope this has made the law clearer to you. If not, or if you have any questions, please feel free to leave them in the comments below. I'll be posting on the other laws of motion soon.